feat(theme): palette generator, 1st pass. m3 is accurate, custom schemes still need some love.

README.md

@@ -26,7 +26,7 @@ A lightweight Wayland shell and bar with no Qt or GTK dependency.
 | Keyboard | `xkbcommon` |
 | Rendering | `EGL`, `OpenGL ES 3`, `wayland-egl` |
 | Text | `cairo`, `pango`, `pangocairo`, `freetype`, `harfbuzz`, `fontconfig` |
-| Images | `Wuffs` (vendored), `nanosvg` (vendored) |
+| Images | `Wuffs` (vendored), `nanosvg` (vendored), `libwebp` |
 | IPC | `sdbus-c++` |
 | Audio | `libpipewire` |
 | Authentication | `PAM` |
@@ -47,7 +47,7 @@ sudo dnf install meson gcc-c++ just \
   cairo-devel pango-devel \
   libxkbcommon-devel \
   sdbus-cpp-devel pipewire-devel \
-  pam-devel libcurl-devel \
+  pam-devel libcurl-devel libwebp-devel \
   libasan libubsan
 ```
 
@@ -60,7 +60,7 @@ sudo pacman -S meson gcc just \
   cairo pango \
   libxkbcommon \
   sdbus-cpp libpipewire \
-  pam curl \
+  pam curl libwebp \
   gcc-libs
 ```
 
@@ -74,12 +74,14 @@ sudo apt install meson g++ just \
   libcairo2-dev libpango1.0-dev \
   libxkbcommon-dev \
   libsdbus-c++-dev libpipewire-0.3-dev \
-  libpam0g-dev libcurl4-openssl-dev \
+  libpam0g-dev libcurl4-openssl-dev libwebp-dev \
   libasan8 libubsan1
 ```
 
 Vendored (no system package needed): `Wuffs`, `nanosvg`, `tomlplusplus`, `tinyexpr`, `nlohmann/json`.
 
+System packages required beyond the Wayland/GL stack: `libwebp` (VP8 lossy WebP; wuffs handles all other formats).
+
 ## Build
 
 Requires [just](https://github.com/casey/just) and [meson](https://mesonbuild.com/).

meson.build

@@ -59,6 +59,57 @@ tinyexpr_dep = declare_dependency(
   include_directories: include_directories('third_party/tinyexpr', is_system: true),
 )
 
+# ── Vendored: Material Color Utilities (Google) ───────────────────────────────
+# Upstream uses #include "cpp/..." prefixes, so the include root is the
+# material_color_utilities/ dir itself. Built as a quiet static library.
+_mcu_sources = files(
+  'third_party/material_color_utilities/cpp/blend/blend.cc',
+  'third_party/material_color_utilities/cpp/cam/cam.cc',
+  'third_party/material_color_utilities/cpp/cam/hct.cc',
+  'third_party/material_color_utilities/cpp/cam/hct_solver.cc',
+  'third_party/material_color_utilities/cpp/cam/viewing_conditions.cc',
+  'third_party/material_color_utilities/cpp/contrast/contrast.cc',
+  'third_party/material_color_utilities/cpp/dislike/dislike.cc',
+  'third_party/material_color_utilities/cpp/dynamiccolor/dynamic_color.cc',
+  'third_party/material_color_utilities/cpp/dynamiccolor/dynamic_scheme.cc',
+  'third_party/material_color_utilities/cpp/dynamiccolor/material_dynamic_colors.cc',
+  'third_party/material_color_utilities/cpp/palettes/tones.cc',
+  'third_party/material_color_utilities/cpp/quantize/celebi.cc',
+  'third_party/material_color_utilities/cpp/quantize/lab.cc',
+  'third_party/material_color_utilities/cpp/quantize/wsmeans.cc',
+  'third_party/material_color_utilities/cpp/quantize/wu.cc',
+  'third_party/material_color_utilities/cpp/scheme/scheme_content.cc',
+  'third_party/material_color_utilities/cpp/scheme/scheme_expressive.cc',
+  'third_party/material_color_utilities/cpp/scheme/scheme_fidelity.cc',
+  'third_party/material_color_utilities/cpp/scheme/scheme_fruit_salad.cc',
+  'third_party/material_color_utilities/cpp/scheme/scheme_monochrome.cc',
+  'third_party/material_color_utilities/cpp/scheme/scheme_neutral.cc',
+  'third_party/material_color_utilities/cpp/scheme/scheme_rainbow.cc',
+  'third_party/material_color_utilities/cpp/scheme/scheme_tonal_spot.cc',
+  'third_party/material_color_utilities/cpp/scheme/scheme_vibrant.cc',
+  'third_party/material_color_utilities/cpp/score/score.cc',
+  'third_party/material_color_utilities/cpp/temperature/temperature_cache.cc',
+  'third_party/material_color_utilities/cpp/utils/utils.cc',
+)
+_mcu_lib = static_library('material_color_utilities',
+  _mcu_sources,
+  include_directories: include_directories('third_party/material_color_utilities', is_system: true),
+  cpp_args: ['-Wno-pedantic', '-Wno-conversion', '-Wno-shadow', '-Wno-unused-parameter'],
+  override_options: ['warning_level=0'],
+)
+mcu_dep = declare_dependency(
+  link_with: _mcu_lib,
+  include_directories: include_directories('third_party/material_color_utilities', is_system: true),
+)
+
+# ── Vendored: stb_image_resize2 (header-only) ─────────────────────────────────
+stb_dep = declare_dependency(
+  include_directories: include_directories('third_party/stb', is_system: true),
+)
+
+# ── System: libwebp (VP8 lossy WebP; wuffs only handles VP8L lossless) ────────
+libwebp_dep = dependency('libwebp', required: true)
+
 # ── Wayland protocol generation ───────────────────────────────────────────────
 wayland_scanner    = find_program('wayland-scanner')
 wayland_protos_dir = wayland_protos_dep.get_variable('pkgdatadir')
@@ -177,7 +228,7 @@ _noctalia_sources = files(
   'src/render/animation/animation_manager.cpp',
   'src/render/core/shader_program.cpp',
   'src/render/core/texture_manager.cpp',
-  'src/render/core/wuffs_image_decoder.cpp',
+  'src/render/core/image_decoder.cpp',
   'src/render/image_loaders.cpp',
   'src/render/programs/color_glyph_program.cpp',
   'src/render/programs/image_program.cpp',
@@ -272,6 +323,16 @@ _noctalia_sources = files(
   'src/wayland/wayland_seat.cpp',
   'src/wayland/wayland_toplevels.cpp',
   'src/wayland/wayland_workspaces.cpp',
+  'src/theme/scheme.cpp',
+  'src/theme/color.cpp',
+  'src/theme/contrast.cpp',
+  'src/theme/image_loader.cpp',
+  'src/theme/palette_generator.cpp',
+  'src/theme/m3_schemes.cpp',
+  'src/theme/custom_schemes.cpp',
+  'src/theme/json_output.cpp',
+  'src/theme/cli.cpp',
+  'src/ipc/cli.cpp',
 )
 
 if sanitize
@@ -311,6 +372,9 @@ executable('noctalia',
     curl_dep,
     pam_dep,
     tinyexpr_dep,
+    mcu_dep,
+    stb_dep,
+    libwebp_dep,
   ],
   include_directories: _noctalia_inc,
   cpp_args: [

src/ipc/cli.cpp

@@ -0,0 +1,23 @@
+#include "ipc/cli.h"
+
+#include "ipc/ipc_client.h"
+
+#include <cstdio>
+#include <string>
+
+namespace noctalia::ipc {
+
+  int runCli(int argc, char* argv[]) {
+    if (argc < 3) {
+      std::fputs("error: msg requires a command (try: noctalia msg --help)\n", stderr);
+      return 1;
+    }
+    std::string cmd = argv[2];
+    for (int i = 3; i < argc; ++i) {
+      cmd += ' ';
+      cmd += argv[i];
+    }
+    return IpcClient::send(cmd);
+  }
+
+} // namespace noctalia::ipc

src/ipc/cli.h

@@ -0,0 +1,9 @@
+#pragma once
+
+namespace noctalia::ipc {
+
+  // Entry point for `noctalia msg <command> [args...]`. Returns a process exit
+  // code. Forwards the command to the running instance over the IPC socket.
+  int runCli(int argc, char* argv[]);
+
+} // namespace noctalia::ipc

src/main.cpp

@@ -1,32 +1,21 @@
 #include "app/application.h"
 #include "core/log.h"
+#include "ipc/cli.h"
 #include "ipc/ipc_client.h"
+#include "theme/cli.h"
 
+#include <cstdio>
 #include <cstring>
 #include <stdexcept>
-#include <string>
 
-int main(int argc, char* argv[]) {
-  if (argc >= 2 && std::strcmp(argv[1], "msg") == 0) {
-    // noctalia msg <command> [args...]
-    if (argc < 3) {
-      std::fputs("error: msg requires a command (try: noctalia msg --help)\n", stderr);
-      return 1;
-    }
-    std::string cmd = argv[2];
-    for (int i = 3; i < argc; ++i) {
-      cmd += ' ';
-      cmd += argv[i];
-    }
-    return IpcClient::send(cmd);
-  }
+namespace {
 
-  for (int i = 1; i < argc; ++i) {
-    if (std::strcmp(argv[i], "--version") == 0) {
+  int runTopLevelFlag(const char* flag) {
+    if (std::strcmp(flag, "--version") == 0) {
       std::puts("noctalia v" NOCTALIA_VERSION);
       return 0;
     }
-    if (std::strcmp(argv[i], "--help") == 0) {
+    if (std::strcmp(flag, "--help") == 0) {
       std::puts("Usage: noctalia [OPTIONS]\n"
                 "\n"
                 "Options:\n"
@@ -34,25 +23,45 @@ int main(int argc, char* argv[]) {
                 "  --version  Show version information\n"
                 "\n"
                 "Subcommands:\n"
-                "  msg <command>  Send a command to the running instance\n"
-                "                 Run 'noctalia msg --help' for available commands\n"
+                "  msg <command>    Send a command to the running instance\n"
+                "                   Run 'noctalia msg --help' for available commands\n"
+                "  theme <image>    Generate a color palette from an image\n"
+                "                   Run 'noctalia theme --help' for options\n"
                 "\n"
                 "For more information and documentation, visit:\n"
                 "  https://noctalia.dev");
       return 0;
     }
+    return -1;
   }
 
-  if (IpcClient::isRunning()) {
-    std::fputs("error: noctalia is already running\n", stderr);
-    return 1;
+  int runShell() {
+    if (IpcClient::isRunning()) {
+      std::fputs("error: noctalia is already running\n", stderr);
+      return 1;
+    }
+    try {
+      Application app;
+      app.run();
+    } catch (const std::exception& e) {
+      logError("fatal: {}", e.what());
+      return 1;
+    }
+    return 0;
   }
 
-  try {
-    Application app;
-    app.run();
-  } catch (const std::exception& e) {
-    logError("fatal: {}", e.what());
-    return 1;
+} // namespace
+
+int main(int argc, char* argv[]) {
+  if (argc >= 2) {
+    if (std::strcmp(argv[1], "theme") == 0) return noctalia::theme::runCli(argc, argv);
+    if (std::strcmp(argv[1], "msg") == 0) return noctalia::ipc::runCli(argc, argv);
   }
+
+  for (int i = 1; i < argc; ++i) {
+    const int rc = runTopLevelFlag(argv[i]);
+    if (rc >= 0) return rc;
+  }
+
+  return runShell();
 }

src/render/core/image_decoder.cpp

@@ -1,10 +1,14 @@
-#include "render/core/wuffs_image_decoder.h"
+#include "render/core/image_decoder.h"
 
+#include <cstdio>
+#include <cstdlib>
 #include <cstring>
 #include <utility>
 
+#include <webp/decode.h>
+
 #define WUFFS_IMPLEMENTATION
-#include "wuffs-unsupported-snapshot.c"
+#include "wuffs-v0.4.c"
 
 namespace {
 
@@ -17,6 +21,33 @@ public:
   }
 };
 
+// Returns true if the buffer starts with the RIFF....WEBP signature.
+bool isWebP(const std::uint8_t* data, std::size_t size) {
+  return size >= 12 &&
+         data[0] == 'R' && data[1] == 'I' && data[2] == 'F' && data[3] == 'F' &&
+         data[8] == 'W' && data[9] == 'E' && data[10] == 'B' && data[11] == 'P';
+}
+
+std::optional<DecodedRasterImage> decodeWebP(
+    const std::uint8_t* data, std::size_t size, std::string* errorMessage) {
+  int width = 0, height = 0;
+  std::uint8_t* rgba = WebPDecodeRGBA(data, size, &width, &height);
+  if (rgba == nullptr) {
+    if (errorMessage != nullptr)
+      *errorMessage = "libwebp: failed to decode WebP image";
+    return std::nullopt;
+  }
+
+  DecodedRasterImage decoded;
+  decoded.width = width;
+  decoded.height = height;
+  std::size_t bytes = static_cast<std::size_t>(width) * static_cast<std::size_t>(height) * 4;
+  decoded.pixels.resize(bytes);
+  std::memcpy(decoded.pixels.data(), rgba, bytes);
+  WebPFree(rgba);
+  return decoded;
+}
+
 } // namespace
 
 std::optional<DecodedRasterImage>
@@ -28,6 +59,9 @@ decodeRasterImage(const std::uint8_t* data, std::size_t size, std::string* error
     return std::nullopt;
   }
 
+  if (isWebP(data, size))
+    return decodeWebP(data, size, errorMessage);
+
   auto input = wuffs_aux::sync_io::MemoryInput(data, size);
   auto callbacks = RgbaDecodeCallbacks();
   auto result = wuffs_aux::DecodeImage(callbacks, input);
@@ -53,4 +87,3 @@ decodeRasterImage(const std::uint8_t* data, std::size_t size, std::string* error
   std::memcpy(decoded.pixels.data(), plane.ptr, decoded.pixels.size());
   return decoded;
 }
-

src/render/core/texture_manager.cpp

@@ -12,7 +12,7 @@
 #include <nanosvgrast.h>
 #pragma GCC diagnostic pop
 
-#include "render/core/wuffs_image_decoder.h"
+#include "render/core/image_decoder.h"
 
 #include <algorithm>
 #include <cstring>

src/theme/cli.cpp

@@ -0,0 +1,120 @@
+#include "theme/cli.h"
+
+#include <cstdio>
+#include <cstring>
+#include <fstream>
+#include <string>
+
+#include "theme/image_loader.h"
+#include "theme/json_output.h"
+#include "theme/palette_generator.h"
+#include "theme/scheme.h"
+
+namespace noctalia::theme {
+
+  namespace {
+
+    constexpr const char* kHelpText = "Usage: noctalia theme <image> [options]\n"
+                                      "\n"
+                                      "Generate a color palette from an image. Material You and custom\n"
+                                      "schemes produce very different results.\n"
+                                      "\n"
+                                      "Options:\n"
+                                      "  --scheme <name>   Material You (Material Design 3):\n"
+                                      "                      m3-tonal-spot  (default)\n"
+                                      "                      m3-content\n"
+                                      "                      m3-fruit-salad\n"
+                                      "                      m3-rainbow\n"
+                                      "                      m3-monochrome\n"
+                                      "                    Custom (HSL-space, non-M3):\n"
+                                      "                      vibrant\n"
+                                      "                      faithful\n"
+                                      "                      dysfunctional\n"
+                                      "                      muted\n"
+                                      "  --dark            Emit only the dark variant (default)\n"
+                                      "  --light           Emit only the light variant\n"
+                                      "  --both            Emit both variants under dark/light keys\n"
+                                      "  -o <file>         Write JSON to file instead of stdout";
+
+  } // namespace
+
+  int runCli(int argc, char* argv[]) {
+    const char* imagePath = nullptr;
+    std::string schemeName = "m3-tonal-spot";
+    Variant variant = Variant::Dark;
+    const char* outPath = nullptr;
+
+    for (int i = 2; i < argc; ++i) {
+      const char* a = argv[i];
+      if (std::strcmp(a, "--help") == 0) {
+        std::puts(kHelpText);
+        return 0;
+      }
+      if (std::strcmp(a, "--scheme") == 0 && i + 1 < argc) {
+        schemeName = argv[++i];
+        continue;
+      }
+      if (std::strcmp(a, "--dark") == 0) {
+        variant = Variant::Dark;
+        continue;
+      }
+      if (std::strcmp(a, "--light") == 0) {
+        variant = Variant::Light;
+        continue;
+      }
+      if (std::strcmp(a, "--both") == 0) {
+        variant = Variant::Both;
+        continue;
+      }
+      if (std::strcmp(a, "-o") == 0 && i + 1 < argc) {
+        outPath = argv[++i];
+        continue;
+      }
+      if (!imagePath && a[0] != '-') {
+        imagePath = a;
+        continue;
+      }
+      std::fprintf(stderr, "error: unknown theme argument: %s\n", a);
+      return 1;
+    }
+
+    if (!imagePath) {
+      std::fputs("error: theme requires an image path (try: noctalia theme --help)\n", stderr);
+      return 1;
+    }
+
+    auto schemeOpt = schemeFromString(schemeName);
+    if (!schemeOpt) {
+      std::fprintf(stderr, "error: unknown scheme '%s'\n", schemeName.c_str());
+      return 1;
+    }
+
+    std::string err;
+    auto loaded = loadAndResize(imagePath, *schemeOpt, &err);
+    if (!loaded) {
+      std::fprintf(stderr, "error: failed to load image: %s\n", err.c_str());
+      return 1;
+    }
+
+    auto palette = generate(loaded->rgb, *schemeOpt, &err);
+    if (palette.dark.empty() && palette.light.empty()) {
+      std::fprintf(stderr, "error: palette generation failed: %s\n", err.empty() ? "unknown error" : err.c_str());
+      return 1;
+    }
+
+    const std::string json = toJson(palette, *schemeOpt, variant);
+    if (outPath) {
+      std::ofstream f(outPath);
+      if (!f) {
+        std::fprintf(stderr, "error: cannot open output file: %s\n", outPath);
+        return 1;
+      }
+      f << json << '\n';
+    } else {
+      std::fwrite(json.data(), 1, json.size(), stdout);
+      std::fputc('\n', stdout);
+    }
+    return 0;
+  }
+
+} // namespace noctalia::theme

src/theme/cli.h

@@ -0,0 +1,10 @@
+#pragma once
+
+namespace noctalia::theme {
+
+  // Entry point for `noctalia theme <image> [options]`. Returns a process exit
+  // code. Does not touch Application / event loop / config — pure function of
+  // (argv, stdout, stderr).
+  int runCli(int argc, char* argv[]);
+
+} // namespace noctalia::theme

src/theme/color.cpp

@@ -0,0 +1,130 @@
+#include "theme/color.h"
+
+#include <algorithm>
+#include <cmath>
+#include <cstdio>
+#include <stdexcept>
+
+namespace noctalia::theme {
+
+  namespace {
+
+    int parseHexByte(std::string_view s, size_t offset) {
+      auto digit = [](char c) -> int {
+        if (c >= '0' && c <= '9')
+          return c - '0';
+        if (c >= 'a' && c <= 'f')
+          return c - 'a' + 10;
+        if (c >= 'A' && c <= 'F')
+          return c - 'A' + 10;
+        throw std::invalid_argument("invalid hex digit");
+      };
+      return digit(s[offset]) * 16 + digit(s[offset + 1]);
+    }
+
+    int roundClamp255(double v) {
+      long r = std::lround(v * 255.0);
+      if (r < 0)
+        r = 0;
+      if (r > 255)
+        r = 255;
+      return static_cast<int>(r);
+    }
+
+  } // namespace
+
+  Color Color::fromHex(std::string_view hex) {
+    if (!hex.empty() && hex.front() == '#')
+      hex.remove_prefix(1);
+    if (hex.size() != 6)
+      throw std::invalid_argument("hex must be 6 chars");
+    return Color(parseHexByte(hex, 0), parseHexByte(hex, 2), parseHexByte(hex, 4));
+  }
+
+  Color Color::fromArgb(uint32_t argb) {
+    return Color(static_cast<int>((argb >> 16) & 0xff), static_cast<int>((argb >> 8) & 0xff),
+                 static_cast<int>(argb & 0xff));
+  }
+
+  std::string Color::toHex() const {
+    char buf[8];
+    std::snprintf(buf, sizeof(buf), "#%02x%02x%02x", r & 0xff, g & 0xff, b & 0xff);
+    return std::string(buf);
+  }
+
+  std::tuple<double, double, double> Color::toHsl() const {
+    const double rn = r / 255.0;
+    const double gn = g / 255.0;
+    const double bn = b / 255.0;
+    const double maxC = std::max({rn, gn, bn});
+    const double minC = std::min({rn, gn, bn});
+    const double delta = maxC - minC;
+
+    const double l = (maxC + minC) / 2.0;
+    double h = 0.0;
+    double s = 0.0;
+    if (delta != 0.0) {
+      if (l != 0.0 && l != 1.0) {
+        s = delta / (1.0 - std::fabs(2.0 * l - 1.0));
+      }
+      if (maxC == rn) {
+        // Positive-result fmod so negative ratios wrap cleanly onto [0, 6).
+        double t = std::fmod((gn - bn) / delta, 6.0);
+        if (t < 0.0)
+          t += 6.0;
+        h = 60.0 * t;
+      } else if (maxC == gn) {
+        h = 60.0 * ((bn - rn) / delta + 2.0);
+      } else {
+        h = 60.0 * ((rn - gn) / delta + 4.0);
+      }
+    }
+    return {h, s, l};
+  }
+
+  Color Color::fromHsl(double h, double s, double l) {
+    if (s == 0.0) {
+      int v = roundClamp255(l);
+      return Color(v, v, v);
+    }
+    const double q = (l < 0.5) ? (l * (1.0 + s)) : (l + s - l * s);
+    const double p = 2.0 * l - q;
+    const double hn = h / 360.0;
+
+    auto hueToRgb = [&](double t) -> double {
+      if (t < 0.0)
+        t += 1.0;
+      if (t > 1.0)
+        t -= 1.0;
+      if (t < 1.0 / 6.0)
+        return p + (q - p) * 6.0 * t;
+      if (t < 1.0 / 2.0)
+        return q;
+      if (t < 2.0 / 3.0)
+        return p + (q - p) * (2.0 / 3.0 - t) * 6.0;
+      return p;
+    };
+
+    return Color(roundClamp255(hueToRgb(hn + 1.0 / 3.0)), roundClamp255(hueToRgb(hn)),
+                 roundClamp255(hueToRgb(hn - 1.0 / 3.0)));
+  }
+
+  double hueDistance(double h1, double h2) {
+    const double diff = std::fabs(h1 - h2);
+    return std::min(diff, 360.0 - diff);
+  }
+
+  Color shiftHue(const Color& c, double degrees) {
+    auto [h, s, l] = c.toHsl();
+    double newH = std::fmod(h + degrees, 360.0);
+    if (newH < 0.0)
+      newH += 360.0;
+    return Color::fromHsl(newH, s, l);
+  }
+
+  Color adjustSurface(const Color& base, double sMax, double lTarget) {
+    auto [h, s, _l] = base.toHsl();
+    return Color::fromHsl(h, std::min(s, sMax), lTarget);
+  }
+
+} // namespace noctalia::theme

src/theme/color.h

@@ -0,0 +1,39 @@
+#pragma once
+
+#include <cstdint>
+#include <string>
+#include <tuple>
+
+namespace noctalia::theme {
+
+  // Minimal RGB colour (0-255 per channel) with hex/HSL/ARGB conversions. The
+  // custom schemes operate in HSL space via this type; the M3 schemes go
+  // through HCT instead and only use this for final ARGB → hex emission.
+  struct Color {
+    int r = 0;
+    int g = 0;
+    int b = 0;
+
+    Color() = default;
+    constexpr Color(int red, int green, int blue) : r(red), g(green), b(blue) {}
+
+    static Color fromHex(std::string_view hex); // accepts #RRGGBB or RRGGBB
+    static Color fromHsl(double h, double s, double l);
+    static Color fromArgb(uint32_t argb);
+
+    std::string toHex() const;                        // "#rrggbb"
+    std::tuple<double, double, double> toHsl() const; // (h°, s, l) — h in [0,360)
+    uint32_t toArgb() const { return 0xff000000u | (uint32_t(r) << 16) | (uint32_t(g) << 8) | uint32_t(b); }
+  };
+
+  // Shortest circular hue distance in degrees (result in [0, 180]).
+  double hueDistance(double h1, double h2);
+
+  // Shift a colour's hue by `degrees`, preserving saturation and lightness.
+  Color shiftHue(const Color& c, double degrees);
+
+  // Build a surface colour from `base`: keep its hue, cap saturation at `sMax`,
+  // force lightness to `lTarget`.
+  Color adjustSurface(const Color& base, double sMax, double lTarget);
+
+} // namespace noctalia::theme

src/theme/contrast.cpp

@@ -0,0 +1,69 @@
+#include "theme/contrast.h"
+
+#include <algorithm>
+#include <cmath>
+
+namespace noctalia::theme {
+
+  namespace {
+
+    double linearizeChannel(int c) {
+      const double n = c / 255.0;
+      if (n <= 0.03928)
+        return n / 12.92;
+      return std::pow((n + 0.055) / 1.055, 2.4);
+    }
+
+  } // namespace
+
+  double relativeLuminance(int r, int g, int b) {
+    return 0.2126 * linearizeChannel(r) + 0.7152 * linearizeChannel(g) + 0.0722 * linearizeChannel(b);
+  }
+
+  double contrastRatio(const Color& a, const Color& b) {
+    const double l1 = relativeLuminance(a.r, a.g, a.b);
+    const double l2 = relativeLuminance(b.r, b.g, b.b);
+    const double lighter = std::max(l1, l2);
+    const double darker = std::min(l1, l2);
+    return (lighter + 0.05) / (darker + 0.05);
+  }
+
+  bool isDark(const Color& c) { return relativeLuminance(c.r, c.g, c.b) < 0.179; }
+
+  Color ensureContrast(const Color& foreground, const Color& background, double minRatio, int preferLight) {
+    if (contrastRatio(foreground, background) >= minRatio)
+      return foreground;
+
+    auto [h, s, l] = foreground.toHsl();
+    bool lighten;
+    if (preferLight > 0)
+      lighten = true;
+    else if (preferLight < 0)
+      lighten = false;
+    else
+      lighten = isDark(background);
+
+    double low = lighten ? l : 0.0;
+    double high = lighten ? 1.0 : l;
+
+    Color best = foreground;
+    for (int i = 0; i < 20; ++i) {
+      const double mid = (low + high) / 2.0;
+      Color test = Color::fromHsl(h, s, mid);
+      if (contrastRatio(test, background) >= minRatio) {
+        best = test;
+        if (lighten)
+          high = mid;
+        else
+          low = mid;
+      } else {
+        if (lighten)
+          low = mid;
+        else
+          high = mid;
+      }
+    }
+    return best;
+  }
+
+} // namespace noctalia::theme

src/theme/contrast.h

@@ -0,0 +1,16 @@
+#pragma once
+
+#include "theme/color.h"
+
+namespace noctalia::theme {
+
+  double relativeLuminance(int r, int g, int b);
+  double contrastRatio(const Color& a, const Color& b);
+  bool isDark(const Color& c);
+
+  // Binary-search the foreground's HSL lightness toward black or white until
+  // the WCAG contrast ratio against `background` meets `minRatio`.
+  // preferLight: -1 = darken, +1 = lighten, 0 = auto (lighten if bg is dark).
+  Color ensureContrast(const Color& foreground, const Color& background, double minRatio = 4.5, int preferLight = 0);
+
+} // namespace noctalia::theme

src/theme/image_loader.cpp

@@ -0,0 +1,215 @@
+#include "theme/image_loader.h"
+
+#include <algorithm>
+#include <cmath>
+#include <cstdio>
+#include <cstdlib>
+#include <fstream>
+#include <iterator>
+
+#include "render/core/image_decoder.h"
+
+namespace noctalia::theme {
+
+  namespace {
+
+    constexpr int kTarget = 112;
+
+    std::vector<uint8_t> readFile(std::string_view path, std::string* err) {
+      std::ifstream f(std::string(path), std::ios::binary);
+      if (!f) {
+        if (err)
+          *err = "cannot open file";
+        return {};
+      }
+      return std::vector<uint8_t>((std::istreambuf_iterator<char>(f)), std::istreambuf_iterator<char>());
+    }
+
+    // Hand-port of `image::imageops::sample::resize` (Triangle filter) from
+    // the Rust `image` crate, which is what matugen / material_colors uses.
+    // We need byte-for-byte parity with that implementation because a few
+    // LSB of drift in the resized 112×112 buffer can move the seed to a
+    // different cluster.
+    //
+    // Algorithm: separable scale-aware tent filter, vertical pass first
+    // into a float intermediate (no clamping/rounding between passes), then
+    // horizontal pass with clamp+round-to-nearest into u8. For downsampling
+    // the kernel support widens by the downsample ratio. Operates in 8-bit
+    // sRGB space (no linearisation), matching image crate.
+    //
+    // Pixel-center convention: input pixels are at integer positions; the
+    // output pixel `o` corresponds to input center `(o + 0.5) * ratio`. The
+    // kernel is evaluated at `(i - (inputCenter - 0.5)) / sratio` for input
+    // pixel index `i`. See sample.rs in the image crate for the canonical
+    // form.
+    inline float triangleKernel(float x) {
+      x = x < 0 ? -x : x;
+      return x < 1.0f ? 1.0f - x : 0.0f;
+    }
+
+    // Vertical pass: src is RGBA u8 (srcW × srcH), dst is RGBA f32 (srcW × dstH).
+    void verticalSampleU8ToF32(const uint8_t* src, int srcW, int srcH, float* dst, int dstH) {
+      const float ratio = (float)srcH / (float)dstH;
+      const float sratio = ratio < 1.0f ? 1.0f : ratio;
+      const float srcSupport = 1.0f * sratio;
+
+      std::vector<float> ws;
+      for (int outy = 0; outy < dstH; ++outy) {
+        const float inputyOrig = ((float)outy + 0.5f) * ratio;
+        int left = (int)std::floor(inputyOrig - srcSupport);
+        int right = (int)std::ceil(inputyOrig + srcSupport);
+        if (left < 0)
+          left = 0;
+        if (left > srcH - 1)
+          left = srcH - 1;
+        if (right < left + 1)
+          right = left + 1;
+        if (right > srcH)
+          right = srcH;
+        const float inputy = inputyOrig - 0.5f;
+
+        ws.clear();
+        float sum = 0.0f;
+        for (int i = left; i < right; ++i) {
+          float w = triangleKernel(((float)i - inputy) / sratio);
+          ws.push_back(w);
+          sum += w;
+        }
+        for (auto& w : ws)
+          w /= sum;
+
+        for (int x = 0; x < srcW; ++x) {
+          float t0 = 0, t1 = 0, t2 = 0, t3 = 0;
+          for (int k = 0; k < (int)ws.size(); ++k) {
+            const uint8_t* p = src + ((left + k) * srcW + x) * 4;
+            const float w = ws[k];
+            t0 += (float)p[0] * w;
+            t1 += (float)p[1] * w;
+            t2 += (float)p[2] * w;
+            t3 += (float)p[3] * w;
+          }
+          float* dp = dst + (outy * srcW + x) * 4;
+          // No clamp / no round — image crate's vertical_sample writes raw
+          // f32 into Rgba32FImage.
+          dp[0] = t0;
+          dp[1] = t1;
+          dp[2] = t2;
+          dp[3] = t3;
+        }
+      }
+    }
+
+    // Horizontal pass: src is RGBA f32 (srcW × srcH), dst is RGBA u8 (dstW × srcH).
+    void horizontalSampleF32ToU8(const float* src, int srcW, int srcH, uint8_t* dst, int dstW) {
+      const float ratio = (float)srcW / (float)dstW;
+      const float sratio = ratio < 1.0f ? 1.0f : ratio;
+      const float srcSupport = 1.0f * sratio;
+
+      std::vector<float> ws;
+      for (int outx = 0; outx < dstW; ++outx) {
+        const float inputxOrig = ((float)outx + 0.5f) * ratio;
+        int left = (int)std::floor(inputxOrig - srcSupport);
+        int right = (int)std::ceil(inputxOrig + srcSupport);
+        if (left < 0)
+          left = 0;
+        if (left > srcW - 1)
+          left = srcW - 1;
+        if (right < left + 1)
+          right = left + 1;
+        if (right > srcW)
+          right = srcW;
+        const float inputx = inputxOrig - 0.5f;
+
+        ws.clear();
+        float sum = 0.0f;
+        for (int i = left; i < right; ++i) {
+          float w = triangleKernel(((float)i - inputx) / sratio);
+          ws.push_back(w);
+          sum += w;
+        }
+        for (auto& w : ws)
+          w /= sum;
+
+        for (int y = 0; y < srcH; ++y) {
+          float t0 = 0, t1 = 0, t2 = 0, t3 = 0;
+          for (int k = 0; k < (int)ws.size(); ++k) {
+            const float* p = src + (y * srcW + (left + k)) * 4;
+            const float w = ws[k];
+            t0 += p[0] * w;
+            t1 += p[1] * w;
+            t2 += p[2] * w;
+            t3 += p[3] * w;
+          }
+          // FloatNearest(clamp(t, 0, 255)) → u8. Rust's f32::round is
+          // round-half-away-from-zero.
+          auto toU8 = [](float v) -> uint8_t {
+            if (v < 0)
+              v = 0;
+            if (v > 255)
+              v = 255;
+            float r = v < 0.0f ? std::ceil(v - 0.5f) : std::floor(v + 0.5f);
+            return (uint8_t)r;
+          };
+          uint8_t* dp = dst + (y * dstW + outx) * 4;
+          dp[0] = toU8(t0);
+          dp[1] = toU8(t1);
+          dp[2] = toU8(t2);
+          dp[3] = toU8(t3);
+        }
+      }
+    }
+
+    std::vector<uint8_t> triangleResize(const uint8_t* srcRgba, int srcW, int srcH, int dstW, int dstH) {
+      // image crate order: vertical first → Rgba32FImage(srcW × dstH)
+      //                    horizontal      → RgbaImage(dstW × dstH)
+      std::vector<float> tmp((size_t)srcW * (size_t)dstH * 4);
+      verticalSampleU8ToF32(srcRgba, srcW, srcH, tmp.data(), dstH);
+      std::vector<uint8_t> dst((size_t)dstW * (size_t)dstH * 4);
+      horizontalSampleF32ToU8(tmp.data(), srcW, dstH, dst.data(), dstW);
+      return dst;
+    }
+
+  } // namespace
+
+  std::optional<LoadedImage> loadAndResize(std::string_view path, Scheme scheme, std::string* errorMessage) {
+    auto bytes = readFile(path, errorMessage);
+    if (bytes.empty())
+      return std::nullopt;
+
+    auto decoded = decodeRasterImage(bytes.data(), bytes.size(), errorMessage);
+    if (!decoded)
+      return std::nullopt;
+
+    const int srcW = decoded->width;
+    const int srcH = decoded->height;
+    if (srcW <= 0 || srcH <= 0) {
+      if (errorMessage)
+        *errorMessage = "invalid image dimensions";
+      return std::nullopt;
+    }
+
+    // Force-resize to 112×112 (aspect ratio ignored, matching matugen which
+    // calls `image::imageops::resize(112, 112, Triangle)` — that's a force
+    // resize despite the name).
+    //
+    // Implementation: hand-port of the Rust `image` crate's Triangle resize
+    // (separable scale-aware tent filter, no sRGB linearisation). We tried
+    // stb_image_resize2 first but its named filters (TRIANGLE/MITCHELL/...)
+    // use fixed unit support and severely alias at large downsample ratios;
+    // its BOX filter scales but is uniform-weight, leaving a residual ~10°
+    // hue offset on certain images. The custom port matches the image crate
+    // (matugen's underlying lib) within ≤ 2 LSB per channel.
+    (void)scheme;
+    std::vector<uint8_t> resizedRgba = triangleResize(decoded->pixels.data(), srcW, srcH, kTarget, kTarget);
+
+    LoadedImage out;
+    out.rgb.resize(kTarget * kTarget * 3);
+    for (int i = 0; i < kTarget * kTarget; ++i) {
+      out.rgb[i * 3 + 0] = resizedRgba[i * 4 + 0];
+      out.rgb[i * 3 + 1] = resizedRgba[i * 4 + 1];
+      out.rgb[i * 3 + 2] = resizedRgba[i * 4 + 2];
+    }
+    return out;
+  }
+
+} // namespace noctalia::theme

src/theme/image_loader.h

@@ -0,0 +1,26 @@
+#pragma once
+
+#include <cstdint>
+#include <optional>
+#include <string>
+#include <string_view>
+#include <vector>
+
+#include "theme/scheme.h"
+
+namespace noctalia::theme {
+
+  // A 112×112 RGB pixel buffer ready for quantization/clustering. No alpha.
+  // 112 * 112 * 3 = 37632 bytes.
+  struct LoadedImage {
+    std::vector<uint8_t> rgb; // size = 112 * 112 * 3
+    int width = 112;
+    int height = 112;
+  };
+
+  // Load `path`, decode via Wuffs, and resize to exactly 112×112 (aspect ratio
+  // squashed) with alpha stripped. The resize filter is scheme-dependent:
+  // triangle for M3 schemes, box for the custom schemes.
+  std::optional<LoadedImage> loadAndResize(std::string_view path, Scheme scheme, std::string* errorMessage = nullptr);
+
+} // namespace noctalia::theme

src/theme/json_output.cpp

@@ -0,0 +1,46 @@
+#include "theme/json_output.h"
+
+#include <cstdio>
+
+#include <json.hpp>
+
+#include "theme/tokens.h"
+
+namespace noctalia::theme {
+
+  namespace {
+
+    std::string hexString(uint32_t argb) {
+      char buf[8];
+      std::snprintf(buf, sizeof(buf), "#%06x", argb & 0x00ffffffu);
+      return std::string(buf);
+    }
+
+    nlohmann::ordered_json tokenMap(const std::unordered_map<std::string, uint32_t>& tokens) {
+      nlohmann::ordered_json out = nlohmann::ordered_json::object();
+      for (size_t i = 0; i < kTokenCount; ++i) {
+        const std::string key(kTokens[i]);
+        auto it = tokens.find(key);
+        if (it != tokens.end()) {
+          out[key] = hexString(it->second);
+        } else {
+          out[key] = nullptr;
+        }
+      }
+      return out;
+    }
+
+  } // namespace
+
+  std::string toJson(const GeneratedPalette& palette, Scheme /*scheme*/, Variant variant) {
+    if (variant == Variant::Dark)
+      return tokenMap(palette.dark).dump(2);
+    if (variant == Variant::Light)
+      return tokenMap(palette.light).dump(2);
+    nlohmann::ordered_json root = nlohmann::ordered_json::object();
+    root["dark"] = tokenMap(palette.dark);
+    root["light"] = tokenMap(palette.light);
+    return root.dump(2);
+  }
+
+} // namespace noctalia::theme

src/theme/json_output.h

@@ -0,0 +1,17 @@
+#pragma once
+
+#include <string>
+
+#include "theme/palette.h"
+#include "theme/scheme.h"
+
+namespace noctalia::theme {
+
+  enum class Variant { Dark, Light, Both };
+
+  // Serialize a GeneratedPalette to JSON. Values are "#rrggbb" strings emitted
+  // in the canonical iteration order from tokens.h. `Both` wraps dark+light in
+  // `{"dark": {...}, "light": {...}}`; `Dark`/`Light` emit a flat token map.
+  std::string toJson(const GeneratedPalette& palette, Scheme scheme, Variant variant);
+
+} // namespace noctalia::theme

src/theme/m3_schemes.cpp

@@ -0,0 +1,449 @@
+#include <algorithm>
+#include <cmath>
+#include <cstdint>
+#include <cstdio>
+#include <cstdlib>
+#include <memory>
+#include <string>
+#include <unordered_map>
+#include <utility>
+#include <vector>
+
+#include "cpp/cam/cam.h"
+#include "cpp/cam/hct.h"
+#include "cpp/dynamiccolor/dynamic_scheme.h"
+#include "cpp/dynamiccolor/material_dynamic_colors.h"
+#include "cpp/quantize/lab.h"
+#include "cpp/quantize/wu.h"
+#include "cpp/scheme/scheme_content.h"
+#include "cpp/scheme/scheme_fruit_salad.h"
+#include "cpp/scheme/scheme_monochrome.h"
+#include "cpp/scheme/scheme_rainbow.h"
+#include "cpp/scheme/scheme_tonal_spot.h"
+#include "cpp/utils/utils.h"
+
+#include "theme/palette.h"
+#include "theme/palette_generator.h"
+#include "theme/scheme.h"
+
+// Material Design 3 scheme path. Quantize the resized pixels, score for the
+// dominant colourful seed, build a DynamicScheme, then pull each token via
+// MaterialDynamicColors. Matches matugen's pipeline (Rust material_colors
+// crate) one-for-one.
+
+namespace mcu = material_color_utilities;
+
+namespace noctalia::theme {
+
+  namespace {
+
+    // ─── Matugen-faithful quant + score ────────────────────────────────
+    //
+    // MCU's QuantizeCelebi → RankedSuggestions diverges from the Rust
+    // material_colors crate (matugen's underlying lib) in two subtle places
+    // that swap seed picks on certain images:
+    //
+    //   1. MCU's wsmeans.cc sorts swatches by population descending and then
+    //      stores them in std::map<Argb,uint32_t>, so iteration order is
+    //      key-sorted (alpha by argb). The Rust version skips the sort and
+    //      uses IndexMap (insertion order = cluster index order from wu).
+    //   2. MCU's score.cc uses unstable std::sort to rank scored HCTs;
+    //      the Rust version uses stable sort_by.
+    //
+    // Same constants, same math otherwise. We fork wsmeans-result-build and
+    // score here so the seed matches matugen byte-for-byte. Wu can stay as
+    // MCU's — it's purely numeric and produces identical output.
+
+    struct ClusterEntry {
+      mcu::Argb argb;
+      uint32_t population;
+    };
+
+    struct DistanceToIndex {
+      double distance = 0.0;
+      int index = 0;
+      bool operator<(const DistanceToIndex& a) const { return distance < a.distance; }
+    };
+
+    // Hand-port of material_colors Rust QuantizerWsmeans::quantize. Differs
+    // from MCU's wsmeans.cc in five places that all matter for output parity:
+    //
+    //   • 10 iterations max, not 100.
+    //   • cluster_indices initialised to i % cluster_count (deterministic),
+    //     not rand() % cluster_count.
+    //   • Point reassignment is unconditional when a closer cluster exists,
+    //     no kMinDeltaE = 3.0 threshold.
+    //   • Termination uses points_moved count, not a "did anything change" bool.
+    //   • cluster_count is NOT additionally clamped to starting_clusters.len()
+    //     (matugen will index OOB if you give it fewer seeds than requested).
+    //
+    // The final assembly also preserves cluster index order (matches Rust
+    // IndexMap insertion order) instead of population-sorting + std::map.
+    std::vector<ClusterEntry> wsmeansMatugenOrder(const std::vector<mcu::Argb>& input_pixels,
+                                                  const std::vector<mcu::Argb>& starting_clusters,
+                                                  uint16_t max_colors) {
+      if (max_colors == 0 || input_pixels.empty())
+        return {};
+      if (max_colors > 256)
+        max_colors = 256;
+
+      // Dedupe input pixels in insertion order, building parallel
+      // pixels/points/counts arrays. Matches matugen's IndexMap loop.
+      std::unordered_map<mcu::Argb, int> pixel_to_count;
+      std::vector<uint32_t> pixels;
+      std::vector<mcu::Lab> points;
+      pixels.reserve(input_pixels.size());
+      points.reserve(input_pixels.size());
+      for (mcu::Argb pixel : input_pixels) {
+        auto it = pixel_to_count.find(pixel);
+        if (it != pixel_to_count.end()) {
+          it->second++;
+        } else {
+          pixels.push_back(pixel);
+          points.push_back(mcu::LabFromInt(pixel));
+          pixel_to_count[pixel] = 1;
+        }
+      }
+
+      int cluster_count = std::min((int)max_colors, (int)points.size());
+
+      std::vector<mcu::Lab> clusters;
+      clusters.reserve(starting_clusters.size());
+      for (int argb : starting_clusters)
+        clusters.push_back(mcu::LabFromInt(argb));
+      // matugen relies on Wu returning max_colors entries and would index
+      // OOB otherwise. Clamp here (matches MCU's wsmeans.cc) so we don't
+      // crash on low-cardinality images where Wu returns fewer cubes; the
+      // result still matches matugen for the common case.
+      if (!starting_clusters.empty())
+        cluster_count = std::min(cluster_count, (int)starting_clusters.size());
+
+      // Deterministic init, no rand.
+      std::vector<int> cluster_indices;
+      cluster_indices.reserve(points.size());
+      for (size_t i = 0; i < points.size(); i++)
+        cluster_indices.push_back((int)(i % (size_t)cluster_count));
+
+      std::vector<std::vector<DistanceToIndex>> dmat(cluster_count, std::vector<DistanceToIndex>(cluster_count));
+      int pixel_count_sums[256] = {};
+
+      constexpr int kMaxIterations = 10;
+
+      for (int iter = 0; iter < kMaxIterations; iter++) {
+        // Build pairwise cluster distance matrix, then sort each row IN
+        // PLACE by distance ascending. NB: matugen does the same in-place
+        // sort, which has a curious side effect — see the reassign loop.
+        for (int i = 0; i < cluster_count; i++) {
+          for (int j = i + 1; j < cluster_count; j++) {
+            double d = clusters[i].DeltaE(clusters[j]);
+            dmat[j][i] = {d, i};
+            dmat[i][j] = {d, j};
+          }
+        }
+        for (int i = 0; i < cluster_count; i++) {
+          std::sort(dmat[i].begin(), dmat[i].end());
+        }
+
+        int points_moved = 0;
+        for (size_t i = 0; i < points.size(); i++) {
+          mcu::Lab point = points[i];
+          int prev_idx = cluster_indices[i];
+          double prev_d = point.DeltaE(clusters[prev_idx]);
+          double min_d = prev_d;
+          int new_idx = -1;
+          // Quirk match: matugen's reassign loop reads dmat[prev_idx][j]
+          // (the j-th SMALLEST distance from prev_idx, after the in-place
+          // sort) but compares against clusters[j] (the j-th cluster by
+          // original index). The j on each side refers to a different
+          // thing; the early-out cutoff is monotone in j, so the loop ends
+          // up only checking the first N clusters (in original order) where
+          // N is the count of cluster pairs within 4× of prev_d. We replicate
+          // the same indexing for byte-for-byte parity.
+          for (int j = 0; j < cluster_count; j++) {
+            if (dmat[prev_idx][j].distance >= 4.0 * prev_d)
+              continue;
+            double d = point.DeltaE(clusters[j]);
+            if (d < min_d) {
+              min_d = d;
+              new_idx = j;
+            }
+          }
+          if (new_idx != -1) {
+            points_moved++;
+            cluster_indices[i] = new_idx;
+          }
+        }
+        if (points_moved == 0 && iter > 0)
+          break;
+
+        double sa[256] = {}, sb[256] = {}, sc[256] = {};
+        for (int i = 0; i < cluster_count; i++)
+          pixel_count_sums[i] = 0;
+        for (size_t i = 0; i < points.size(); i++) {
+          int ci = cluster_indices[i];
+          int cnt = pixel_to_count[pixels[i]];
+          pixel_count_sums[ci] += cnt;
+          sa[ci] += points[i].l * cnt;
+          sb[ci] += points[i].a * cnt;
+          sc[ci] += points[i].b * cnt;
+        }
+        for (int i = 0; i < cluster_count; i++) {
+          int cnt = pixel_count_sums[i];
+          if (cnt == 0) {
+            clusters[i] = {0, 0, 0};
+            continue;
+          }
+          clusters[i] = {sa[i] / cnt, sb[i] / cnt, sc[i] / cnt};
+        }
+      }
+
+      // Cluster index order, dedupe by argb, drop empties. Matches matugen
+      // wsmeans.rs:275-294 exactly (no population sort, no std::map rekey).
+      std::vector<ClusterEntry> result;
+      for (int i = 0; i < cluster_count; i++) {
+        int cnt = pixel_count_sums[i];
+        if (cnt == 0)
+          continue;
+        mcu::Argb argb = mcu::IntFromLab(clusters[i]);
+        bool dup = false;
+        for (auto& e : result) {
+          if (e.argb == argb) {
+            dup = true;
+            break;
+          }
+        }
+        if (dup)
+          continue;
+        result.push_back({argb, (uint32_t)cnt});
+      }
+      return result;
+    }
+
+    // Hand-port of material_colors Rust Score::score (score.rs). Identical
+    // math to MCU's RankedSuggestions, but iterates clusters in input order
+    // and uses std::stable_sort.
+    std::vector<mcu::Argb> scoreMatugen(const std::vector<ClusterEntry>& clusters, int desired, bool filter) {
+      constexpr double kTargetChroma = 48.0;
+      constexpr double kWeightProportion = 0.7;
+      constexpr double kWeightChromaAbove = 0.3;
+      constexpr double kWeightChromaBelow = 0.1;
+      constexpr double kCutoffChroma = 5.0;
+      constexpr double kCutoffExcitedProportion = 0.01;
+
+      std::vector<mcu::Hct> colors_hct;
+      colors_hct.reserve(clusters.size());
+      std::vector<uint32_t> hue_population(360, 0);
+      double population_sum = 0.0;
+      for (const auto& c : clusters) {
+        mcu::Hct hct(c.argb);
+        colors_hct.push_back(hct);
+        int hue = (int)std::floor(hct.get_hue());
+        hue_population[hue] += c.population;
+        population_sum += c.population;
+      }
+
+      std::vector<double> hue_excited(360, 0.0);
+      for (int hue = 0; hue < 360; hue++) {
+        double prop = hue_population[hue] / population_sum;
+        for (int i = hue - 14; i < hue + 16; i++) {
+          int nh = mcu::SanitizeDegreesInt(i);
+          hue_excited[nh] += prop;
+        }
+      }
+
+      struct Scored {
+        mcu::Hct hct;
+        double score;
+      };
+      std::vector<Scored> scored;
+      scored.reserve(colors_hct.size());
+      for (mcu::Hct hct : colors_hct) {
+        int hue = mcu::SanitizeDegreesInt((int)std::round(hct.get_hue()));
+        double prop = hue_excited[hue];
+        if (filter && (hct.get_chroma() < kCutoffChroma || prop <= kCutoffExcitedProportion))
+          continue;
+        double prop_score = prop * 100.0 * kWeightProportion;
+        double cw = hct.get_chroma() < kTargetChroma ? kWeightChromaBelow : kWeightChromaAbove;
+        double chroma_score = (hct.get_chroma() - kTargetChroma) * cw;
+        scored.push_back({hct, prop_score + chroma_score});
+      }
+      // STABLE sort: matches Rust sort_by, preserves cluster insertion order
+      // when scores tie.
+      std::stable_sort(scored.begin(), scored.end(),
+                       [](const Scored& a, const Scored& b) { return a.score > b.score; });
+
+      std::vector<mcu::Hct> chosen;
+      for (int diff = 90; diff >= 15; diff--) {
+        chosen.clear();
+        for (const auto& e : scored) {
+          mcu::Hct hct = e.hct;
+          bool dup = false;
+          for (const auto& ch : chosen) {
+            if (mcu::DiffDegrees(hct.get_hue(), ch.get_hue()) < diff) {
+              dup = true;
+              break;
+            }
+          }
+          if (!dup) {
+            chosen.push_back(hct);
+            if ((int)chosen.size() >= desired)
+              break;
+          }
+        }
+        if ((int)chosen.size() >= desired)
+          break;
+      }
+
+      std::vector<mcu::Argb> out;
+      if (chosen.empty())
+        out.push_back(0xff4285f4u);
+      for (auto& h : chosen)
+        out.push_back(h.ToInt());
+      return out;
+    }
+
+    // Build pixels → wu seeds → wsmeans (matugen order) → chroma filter →
+    // matugen-style score → first ranked.
+    mcu::Argb extractSeed(const std::vector<uint8_t>& rgb112) {
+      std::vector<mcu::Argb> pixels;
+      pixels.reserve(rgb112.size() / 3);
+      for (size_t i = 0; i + 2 < rgb112.size(); i += 3) {
+        const uint32_t r = rgb112[i + 0];
+        const uint32_t g = rgb112[i + 1];
+        const uint32_t b = rgb112[i + 2];
+        pixels.push_back(0xff000000u | (r << 16) | (g << 8) | b);
+      }
+
+      // Matches QuantizeCelebi: drop transparent, run wu for seeds, then
+      // wsmeans. Wu is unchanged from MCU.
+      std::vector<mcu::Argb> opaque;
+      opaque.reserve(pixels.size());
+      for (mcu::Argb p : pixels) {
+        if (mcu::IsOpaque(p))
+          opaque.push_back(p);
+      }
+      auto wu_seeds = mcu::QuantizeWu(opaque, 128);
+      auto clusters = wsmeansMatugenOrder(opaque, wu_seeds, 128);
+
+      // Drop low-chroma clusters before scoring (matches matugen's
+      // get_source_color_from_image, which calls IndexMap::retain on the
+      // quantizer output). This DOES skew the proportions in score, but
+      // matugen ships it that way and we need bug-for-bug parity.
+      clusters.erase(std::remove_if(clusters.begin(), clusters.end(),
+                                    [](const ClusterEntry& c) { return mcu::CamFromInt(c.argb).chroma < 5.0; }),
+                     clusters.end());
+
+      auto ranked = scoreMatugen(clusters, 4, true);
+      return ranked.empty() ? 0xff4285f4u : ranked.front();
+    }
+
+    std::unique_ptr<mcu::DynamicScheme> makeScheme(const mcu::Hct& source, Scheme scheme, bool isDark) {
+      switch (scheme) {
+      case Scheme::TonalSpot:
+        return std::make_unique<mcu::SchemeTonalSpot>(source, isDark, 0.0);
+      case Scheme::Content:
+        return std::make_unique<mcu::SchemeContent>(source, isDark, 0.0);
+      case Scheme::FruitSalad:
+        return std::make_unique<mcu::SchemeFruitSalad>(source, isDark, 0.0);
+      case Scheme::Rainbow:
+        return std::make_unique<mcu::SchemeRainbow>(source, isDark, 0.0);
+      case Scheme::Monochrome:
+        return std::make_unique<mcu::SchemeMonochrome>(source, isDark, 0.0);
+      default:
+        // Custom schemes are not handled here.
+        return std::make_unique<mcu::SchemeTonalSpot>(source, isDark, 0.0);
+      }
+    }
+
+    std::unordered_map<std::string, uint32_t> buildTokenMap(mcu::DynamicScheme& s) {
+      std::unordered_map<std::string, uint32_t> m;
+      auto set = [&](const char* k, mcu::DynamicColor dc) { m[k] = dc.GetArgb(s); };
+
+      // Primary group
+      set("primary", mcu::MaterialDynamicColors::Primary());
+      set("on_primary", mcu::MaterialDynamicColors::OnPrimary());
+      set("primary_container", mcu::MaterialDynamicColors::PrimaryContainer());
+      set("on_primary_container", mcu::MaterialDynamicColors::OnPrimaryContainer());
+      set("inverse_primary", mcu::MaterialDynamicColors::InversePrimary());
+      set("surface_tint", mcu::MaterialDynamicColors::SurfaceTint());
+
+      // Secondary group
+      set("secondary", mcu::MaterialDynamicColors::Secondary());
+      set("on_secondary", mcu::MaterialDynamicColors::OnSecondary());
+      set("secondary_container", mcu::MaterialDynamicColors::SecondaryContainer());
+      set("on_secondary_container", mcu::MaterialDynamicColors::OnSecondaryContainer());
+
+      // Tertiary group
+      set("tertiary", mcu::MaterialDynamicColors::Tertiary());
+      set("on_tertiary", mcu::MaterialDynamicColors::OnTertiary());
+      set("tertiary_container", mcu::MaterialDynamicColors::TertiaryContainer());
+      set("on_tertiary_container", mcu::MaterialDynamicColors::OnTertiaryContainer());
+
+      // Error group
+      set("error", mcu::MaterialDynamicColors::Error());
+      set("on_error", mcu::MaterialDynamicColors::OnError());
+      set("error_container", mcu::MaterialDynamicColors::ErrorContainer());
+      set("on_error_container", mcu::MaterialDynamicColors::OnErrorContainer());
+
+      // Surface
+      set("surface", mcu::MaterialDynamicColors::Surface());
+      set("on_surface", mcu::MaterialDynamicColors::OnSurface());
+      set("surface_variant", mcu::MaterialDynamicColors::SurfaceVariant());
+      set("on_surface_variant", mcu::MaterialDynamicColors::OnSurfaceVariant());
+      set("surface_dim", mcu::MaterialDynamicColors::SurfaceDim());
+      set("surface_bright", mcu::MaterialDynamicColors::SurfaceBright());
+
+      // Surface containers
+      set("surface_container_lowest", mcu::MaterialDynamicColors::SurfaceContainerLowest());
+      set("surface_container_low", mcu::MaterialDynamicColors::SurfaceContainerLow());
+      set("surface_container", mcu::MaterialDynamicColors::SurfaceContainer());
+      set("surface_container_high", mcu::MaterialDynamicColors::SurfaceContainerHigh());
+      set("surface_container_highest", mcu::MaterialDynamicColors::SurfaceContainerHighest());
+
+      // Outline + shadow/scrim
+      set("outline", mcu::MaterialDynamicColors::Outline());
+      set("outline_variant", mcu::MaterialDynamicColors::OutlineVariant());
+      set("shadow", mcu::MaterialDynamicColors::Shadow());
+      set("scrim", mcu::MaterialDynamicColors::Scrim());
+
+      // Inverse
+      set("inverse_surface", mcu::MaterialDynamicColors::InverseSurface());
+      set("inverse_on_surface", mcu::MaterialDynamicColors::InverseOnSurface());
+
+      // Background (alias of surface per MD3 spec)
+      set("background", mcu::MaterialDynamicColors::Background());
+      set("on_background", mcu::MaterialDynamicColors::OnBackground());
+
+      // Fixed colors — identical across light/dark.
+      set("primary_fixed", mcu::MaterialDynamicColors::PrimaryFixed());
+      set("primary_fixed_dim", mcu::MaterialDynamicColors::PrimaryFixedDim());
+      set("on_primary_fixed", mcu::MaterialDynamicColors::OnPrimaryFixed());
+      set("on_primary_fixed_variant", mcu::MaterialDynamicColors::OnPrimaryFixedVariant());
+      set("secondary_fixed", mcu::MaterialDynamicColors::SecondaryFixed());
+      set("secondary_fixed_dim", mcu::MaterialDynamicColors::SecondaryFixedDim());
+      set("on_secondary_fixed", mcu::MaterialDynamicColors::OnSecondaryFixed());
+      set("on_secondary_fixed_variant", mcu::MaterialDynamicColors::OnSecondaryFixedVariant());
+      set("tertiary_fixed", mcu::MaterialDynamicColors::TertiaryFixed());
+      set("tertiary_fixed_dim", mcu::MaterialDynamicColors::TertiaryFixedDim());
+      set("on_tertiary_fixed", mcu::MaterialDynamicColors::OnTertiaryFixed());
+      set("on_tertiary_fixed_variant", mcu::MaterialDynamicColors::OnTertiaryFixedVariant());
+
+      return m;
+    }
+
+  } // namespace
+
+  GeneratedPalette generateMaterial(const std::vector<uint8_t>& rgb112, Scheme scheme) {
+    const mcu::Argb seed = extractSeed(rgb112);
+    const mcu::Hct source(seed);
+
+    auto darkScheme = makeScheme(source, scheme, true);
+    auto lightScheme = makeScheme(source, scheme, false);
+
+    GeneratedPalette out;
+    out.dark = buildTokenMap(*darkScheme);
+    out.light = buildTokenMap(*lightScheme);
+    return out;
+  }
+
+} // namespace noctalia::theme

src/theme/palette.h

@@ -0,0 +1,17 @@
+#pragma once
+
+#include <cstdint>
+#include <string>
+#include <unordered_map>
+
+namespace noctalia::theme {
+
+  // A fully-generated palette, keyed by the token names from tokens.h. Values
+  // are packed ARGB (0xffRRGGBB). Serialization to "#rrggbb" lives in
+  // json_output.cpp.
+  struct GeneratedPalette {
+    std::unordered_map<std::string, uint32_t> dark;
+    std::unordered_map<std::string, uint32_t> light;
+  };
+
+} // namespace noctalia::theme

src/theme/palette_generator.cpp

@@ -0,0 +1,16 @@
+#include "theme/palette_generator.h"
+
+namespace noctalia::theme {
+
+  GeneratedPalette generate(const std::vector<uint8_t>& rgb112, Scheme scheme, std::string* errorMessage) {
+    if (rgb112.size() != 112u * 112u * 3u) {
+      if (errorMessage)
+        *errorMessage = "expected 112x112x3 pixel buffer";
+      return {};
+    }
+    if (isMaterialScheme(scheme))
+      return generateMaterial(rgb112, scheme);
+    return generateCustom(rgb112, scheme);
+  }
+
+} // namespace noctalia::theme

src/theme/palette_generator.h

@@ -0,0 +1,24 @@
+#pragma once
+
+#include <cstdint>
+#include <string>
+#include <vector>
+
+#include "theme/palette.h"
+#include "theme/scheme.h"
+
+namespace noctalia::theme {
+
+  // Top-level entry point. Accepts a forced-112×112 RGB (no alpha) pixel buffer
+  // and a scheme; dispatches to the M3 (MCU-based) or custom (HSL-based) path
+  // and returns a fully-populated dark+light palette.
+  //
+  // The buffer must contain exactly 112 * 112 * 3 bytes. Returns an empty
+  // palette and writes an error message if generation fails.
+  GeneratedPalette generate(const std::vector<uint8_t>& rgb112, Scheme scheme, std::string* errorMessage = nullptr);
+
+  // Internal paths — exposed for unit testing / analysis tool reuse.
+  GeneratedPalette generateMaterial(const std::vector<uint8_t>& rgb112, Scheme scheme);
+  GeneratedPalette generateCustom(const std::vector<uint8_t>& rgb112, Scheme scheme);
+
+} // namespace noctalia::theme

src/theme/scheme.cpp

@@ -0,0 +1,51 @@
+#include "theme/scheme.h"
+
+namespace noctalia::theme {
+
+  std::optional<Scheme> schemeFromString(std::string_view s) {
+    if (s == "m3-tonal-spot")
+      return Scheme::TonalSpot;
+    if (s == "m3-content")
+      return Scheme::Content;
+    if (s == "m3-fruit-salad")
+      return Scheme::FruitSalad;
+    if (s == "m3-rainbow")
+      return Scheme::Rainbow;
+    if (s == "m3-monochrome")
+      return Scheme::Monochrome;
+    if (s == "vibrant")
+      return Scheme::Vibrant;
+    if (s == "faithful")
+      return Scheme::Faithful;
+    if (s == "dysfunctional")
+      return Scheme::Dysfunctional;
+    if (s == "muted")
+      return Scheme::Muted;
+    return std::nullopt;
+  }
+
+  std::string_view schemeToString(Scheme s) {
+    switch (s) {
+    case Scheme::TonalSpot:
+      return "m3-tonal-spot";
+    case Scheme::Content:
+      return "m3-content";
+    case Scheme::FruitSalad:
+      return "m3-fruit-salad";
+    case Scheme::Rainbow:
+      return "m3-rainbow";
+    case Scheme::Monochrome:
+      return "m3-monochrome";
+    case Scheme::Vibrant:
+      return "vibrant";
+    case Scheme::Faithful:
+      return "faithful";
+    case Scheme::Dysfunctional:
+      return "dysfunctional";
+    case Scheme::Muted:
+      return "muted";
+    }
+    return "m3-tonal-spot";
+  }
+
+} // namespace noctalia::theme

src/theme/scheme.h

@@ -0,0 +1,38 @@
+#pragma once
+
+#include <optional>
+#include <string>
+#include <string_view>
+
+namespace noctalia::theme {
+
+  // Color generation strategies. The first five are Material Design 3 schemes
+  // (TonalPalette + tone tables, built on top of material_color_utilities).
+  // The last four are custom HSL-space generators with very different
+  // aesthetics — they are not Material You and will produce different output.
+  enum class Scheme {
+    TonalSpot,
+    Content,
+    FruitSalad,
+    Rainbow,
+    Monochrome,
+    Vibrant,
+    Faithful,
+    Dysfunctional,
+    Muted,
+  };
+
+  // True for the Material Design 3 schemes.
+  constexpr bool isMaterialScheme(Scheme s) {
+    return s == Scheme::TonalSpot || s == Scheme::Content || s == Scheme::FruitSalad || s == Scheme::Rainbow ||
+           s == Scheme::Monochrome;
+  }
+
+  // Parse a scheme from its CLI string (e.g. "m3-tonal-spot", "vibrant").
+  // Returns nullopt for unknown values.
+  std::optional<Scheme> schemeFromString(std::string_view s);
+
+  // String form used in CLI / JSON output.
+  std::string_view schemeToString(Scheme s);
+
+} // namespace noctalia::theme

src/theme/tokens.h

@@ -0,0 +1,70 @@
+#pragma once
+
+#include <array>
+#include <string_view>
+
+namespace noctalia::theme {
+
+  // Canonical list of colour tokens emitted in every generated palette. The
+  // order is the iteration order used by json_output. Both the M3 schemes
+  // (TonalPalette + tone tables) and the custom HSL schemes populate the same
+  // key set so consumers can treat them interchangeably.
+  inline constexpr std::array<std::string_view, 51> kTokens = {
+      "primary",
+      "on_primary",
+      "primary_container",
+      "on_primary_container",
+      "primary_fixed",
+      "primary_fixed_dim",
+      "on_primary_fixed",
+      "on_primary_fixed_variant",
+      "surface_tint",
+      "secondary",
+      "on_secondary",
+      "secondary_container",
+      "on_secondary_container",
+      "secondary_fixed",
+      "secondary_fixed_dim",
+      "on_secondary_fixed",
+      "on_secondary_fixed_variant",
+      "tertiary",
+      "on_tertiary",
+      "tertiary_container",
+      "on_tertiary_container",
+      "tertiary_fixed",
+      "tertiary_fixed_dim",
+      "on_tertiary_fixed",
+      "on_tertiary_fixed_variant",
+      "error",
+      "on_error",
+      "error_container",
+      "on_error_container",
+      "surface",
+      "on_surface",
+      "surface_variant",
+      "on_surface_variant",
+      "surface_dim",
+      "surface_bright",
+      "surface_container_lowest",
+      "surface_container_low",
+      "surface_container",
+      "surface_container_high",
+      "surface_container_highest",
+      "outline",
+      "outline_variant",
+      "shadow",
+      "scrim",
+      "inverse_surface",
+      "inverse_on_surface",
+      "inverse_primary",
+      "background",
+      "on_background",
+      // Reserved slots for future expansion; not currently emitted to JSON.
+      "",
+      "",
+  };
+
+  // Number of tokens actually emitted (the trailing reserved slots are skipped).
+  inline constexpr size_t kTokenCount = 49;
+
+} // namespace noctalia::theme

third_party/material_color_utilities/LICENSE

@@ -0,0 +1,191 @@
+
+                                 Apache License
+                           Version 2.0, January 2004
+                        http://www.apache.org/licenses/
+
+   TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
+   1. Definitions.
+
+      "License" shall mean the terms and conditions for use, reproduction,
+      and distribution as defined by Sections 1 through 9 of this document.
+
+      "Licensor" shall mean the copyright owner or entity authorized by
+      the copyright owner that is granting the License.
+
+      "Legal Entity" shall mean the union of the acting entity and all
+      other entities that control, are controlled by, or are under common
+      control with that entity. For the purposes of this definition,
+      "control" means (i) the power, direct or indirect, to cause the
+      direction or management of such entity, whether by contract or
+      otherwise, or (ii) ownership of fifty percent (50%) or more of the
+      outstanding shares, or (iii) beneficial ownership of such entity.
+
+      "You" (or "Your") shall mean an individual or Legal Entity
+      exercising permissions granted by this License.
+
+      "Source" form shall mean the preferred form for making modifications,
+      including but not limited to software source code, documentation
+      source, and configuration files.
+
+      "Object" form shall mean any form resulting from mechanical
+      transformation or translation of a Source form, including but
+      not limited to compiled object code, generated documentation,
+      and conversions to other media types.
+
+      "Work" shall mean the work of authorship, whether in Source or
+      Object form, made available under the License, as indicated by a
+      copyright notice that is included in or attached to the work
+      (an example is provided in the Appendix below).
+
+      "Derivative Works" shall mean any work, whether in Source or Object
+      form, that is based on (or derived from) the Work and for which the
+      editorial revisions, annotations, elaborations, or other modifications
+      represent, as a whole, an original work of authorship. For the purposes
+      of this License, Derivative Works shall not include works that remain
+      separable from, or merely link (or bind by name) to the interfaces of,
+      the Work and Derivative Works thereof.
+
+      "Contribution" shall mean any work of authorship, including
+      the original version of the Work and any modifications or additions
+      to that Work or Derivative Works thereof, that is intentionally
+      submitted to Licensor for inclusion in the Work by the copyright owner
+      or by an individual or Legal Entity authorized to submit on behalf of
+      the copyright owner. For the purposes of this definition, "submitted"
+      means any form of electronic, verbal, or written communication sent
+      to the Licensor or its representatives, including but not limited to
+      communication on electronic mailing lists, source code control systems,
+      and issue tracking systems that are managed by, or on behalf of, the
+      Licensor for the purpose of discussing and improving the Work, but
+      excluding communication that is conspicuously marked or otherwise
+      designated in writing by the copyright owner as "Not a Contribution."
+
+      "Contributor" shall mean Licensor and any individual or Legal Entity
+      on behalf of whom a Contribution has been received by Licensor and
+      subsequently incorporated within the Work.
+
+   2. Grant of Copyright License. Subject to the terms and conditions of
+      this License, each Contributor hereby grants to You a perpetual,
+      worldwide, non-exclusive, no-charge, royalty-free, irrevocable
+      copyright license to reproduce, prepare Derivative Works of,
+      publicly display, publicly perform, sublicense, and distribute the
+      Work and such Derivative Works in Source or Object form.
+
+   3. Grant of Patent License. Subject to the terms and conditions of
+      this License, each Contributor hereby grants to You a perpetual,
+      worldwide, non-exclusive, no-charge, royalty-free, irrevocable
+      (except as stated in this section) patent license to make, have made,
+      use, offer to sell, sell, import, and otherwise transfer the Work,
+      where such license applies only to those patent claims licensable
+      by such Contributor that are necessarily infringed by their
+      Contribution(s) alone or by combination of their Contribution(s)
+      with the Work to which such Contribution(s) was submitted. If You
+      institute patent litigation against any entity (including a
+      cross-claim or counterclaim in a lawsuit) alleging that the Work
+      or a Contribution incorporated within the Work constitutes direct
+      or contributory patent infringement, then any patent licenses
+      granted to You under this License for that Work shall terminate
+      as of the date such litigation is filed.
+
+   4. Redistribution. You may reproduce and distribute copies of the
+      Work or Derivative Works thereof in any medium, with or without
+      modifications, and in Source or Object form, provided that You
+      meet the following conditions:
+
+      (a) You must give any other recipients of the Work or
+          Derivative Works a copy of this License; and
+
+      (b) You must cause any modified files to carry prominent notices
+          stating that You changed the files; and
+
+      (c) You must retain, in the Source form of any Derivative Works
+          that You distribute, all copyright, patent, trademark, and
+          attribution notices from the Source form of the Work,
+          excluding those notices that do not pertain to any part of
+          the Derivative Works; and
+
+      (d) If the Work includes a "NOTICE" text file as part of its
+          distribution, then any Derivative Works that You distribute must
+          include a readable copy of the attribution notices contained
+          within such NOTICE file, excluding those notices that do not
+          pertain to any part of the Derivative Works, in at least one
+          of the following places: within a NOTICE text file distributed
+          as part of the Derivative Works; within the Source form or
+          documentation, if provided along with the Derivative Works; or,
+          within a display generated by the Derivative Works, if and
+          wherever such third-party notices normally appear. The contents
+          of the NOTICE file are for informational purposes only and
+          do not modify the License. You may add Your own attribution
+          notices within Derivative Works that You distribute, alongside
+          or as an addendum to the NOTICE text from the Work, provided
+          that such additional attribution notices cannot be construed
+          as modifying the License.
+
+      You may add Your own copyright statement to Your modifications and
+      may provide additional or different license terms and conditions
+      for use, reproduction, or distribution of Your modifications, or
+      for any such Derivative Works as a whole, provided Your use,
+      reproduction, and distribution of the Work otherwise complies with
+      the conditions stated in this License.
+
+   5. Submission of Contributions. Unless You explicitly state otherwise,
+      any Contribution intentionally submitted for inclusion in the Work
+      by You to the Licensor shall be under the terms and conditions of
+      this License, without any additional terms or conditions.
+      Notwithstanding the above, nothing herein shall supersede or modify
+      the terms of any separate license agreement you may have executed
+      with Licensor regarding such Contributions.
+
+   6. Trademarks. This License does not grant permission to use the trade
+      names, trademarks, service marks, or product names of the Licensor,
+      except as required for reasonable and customary use in describing the
+      origin of the Work and reproducing the content of the NOTICE file.
+
+   7. Disclaimer of Warranty. Unless required by applicable law or
+      agreed to in writing, Licensor provides the Work (and each
+      Contributor provides its Contributions) on an "AS IS" BASIS,
+      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+      implied, including, without limitation, any warranties or conditions
+      of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A
+      PARTICULAR PURPOSE. You are solely responsible for determining the
+      appropriateness of using or redistributing the Work and assume any
+      risks associated with Your exercise of permissions under this License.
+
+   8. Limitation of Liability. In no event and under no legal theory,
+      whether in tort (including negligence), contract, or otherwise,
+      unless required by applicable law (such as deliberate and grossly
+      negligent acts) or agreed to in writing, shall any Contributor be
+      liable to You for damages, including any direct, indirect, special,
+      incidental, or consequential damages of any character arising as a
+      result of this License or out of the use or inability to use the
+      Work (including but not limited to damages for loss of goodwill,
+      work stoppage, computer failure or malfunction, or any and all
+      other commercial damages or losses), even if such Contributor
+      has been advised of the possibility of such damages.
+
+   9. Accepting Warranty or Additional Liability. While redistributing
+      the Work or Derivative Works thereof, You may choose to offer,
+      and charge a fee for, acceptance of support, warranty, indemnity,
+      or other liability obligations and/or rights consistent with this
+      License. However, in accepting such obligations, You may act only
+      on Your own behalf and on Your sole responsibility, not on behalf
+      of any other Contributor, and only if You agree to indemnify,
+      defend, and hold each Contributor harmless for any liability
+      incurred by, or claims asserted against, such Contributor by reason
+      of your accepting any such warranty or additional liability.
+
+   END OF TERMS AND CONDITIONS
+
+   Copyright 2021 Google LLC
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.

third_party/material_color_utilities/cpp/blend/blend.cc

@@ -0,0 +1,71 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "cpp/blend/blend.h"
+
+#include <algorithm>
+#include <cstdint>
+
+#include "cpp/cam/cam.h"
+#include "cpp/cam/hct.h"
+#include "cpp/cam/viewing_conditions.h"
+#include "cpp/utils/utils.h"
+
+namespace material_color_utilities {
+
+Argb BlendHarmonize(const Argb design_color, const Argb key_color) {
+  Hct from_hct(design_color);
+  Hct to_hct(key_color);
+  double difference_degrees = DiffDegrees(from_hct.get_hue(), to_hct.get_hue());
+  double rotation_degrees = std::min(difference_degrees * 0.5, 15.0);
+  double output_hue = SanitizeDegreesDouble(
+      from_hct.get_hue() +
+      rotation_degrees *
+          RotationDirection(from_hct.get_hue(), to_hct.get_hue()));
+  from_hct.set_hue(output_hue);
+  return from_hct.ToInt();
+}
+
+Argb BlendHctHue(const Argb from, const Argb to, const double amount) {
+  int ucs = BlendCam16Ucs(from, to, amount);
+  Hct ucs_hct(ucs);
+  Hct from_hct(from);
+  from_hct.set_hue(ucs_hct.get_hue());
+  return from_hct.ToInt();
+}
+
+Argb BlendCam16Ucs(const Argb from, const Argb to, const double amount) {
+  Cam from_cam = CamFromInt(from);
+  Cam to_cam = CamFromInt(to);
+
+  const double a_j = from_cam.jstar;
+  const double a_a = from_cam.astar;
+  const double a_b = from_cam.bstar;
+
+  const double b_j = to_cam.jstar;
+  const double b_a = to_cam.astar;
+  const double b_b = to_cam.bstar;
+
+  const double jstar = a_j + (b_j - a_j) * amount;
+  const double astar = a_a + (b_a - a_a) * amount;
+  const double bstar = a_b + (b_b - a_b) * amount;
+
+  const Cam blended = CamFromUcsAndViewingConditions(jstar, astar, bstar,
+                                                     kDefaultViewingConditions);
+  return IntFromCam(blended);
+}
+
+}  // namespace material_color_utilities

third_party/material_color_utilities/cpp/blend/blend.h

@@ -0,0 +1,31 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CPP_BLEND_BLEND_H_
+#define CPP_BLEND_BLEND_H_
+
+#include <cstdint>
+
+#include "cpp/utils/utils.h"
+
+namespace material_color_utilities {
+
+Argb BlendHarmonize(const Argb design_color, const Argb key_color);
+Argb BlendHctHue(const Argb from, const Argb to, const double amount);
+Argb BlendCam16Ucs(const Argb from, const Argb to, const double amount);
+
+}  // namespace material_color_utilities
+#endif  // CPP_BLEND_BLEND_H_

third_party/material_color_utilities/cpp/cam/cam.cc

@@ -0,0 +1,263 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "cpp/cam/cam.h"
+
+#include <assert.h>
+#include <math.h>
+
+#include "cpp/cam/hct_solver.h"
+#include "cpp/cam/viewing_conditions.h"
+#include "cpp/utils/utils.h"
+
+namespace material_color_utilities {
+
+Cam CamFromJchAndViewingConditions(double j, double c, double h,
+                                   ViewingConditions viewing_conditions);
+
+Cam CamFromUcsAndViewingConditions(
+    double jstar, double astar, double bstar,
+    const ViewingConditions &viewing_conditions) {
+  const double a = astar;
+  const double b = bstar;
+  const double m = sqrt(a * a + b * b);
+  const double m_2 = (exp(m * 0.0228) - 1.0) / 0.0228;
+  const double c = m_2 / viewing_conditions.fl_root;
+  double h = atan2(b, a) * (180.0 / kPi);
+  if (h < 0.0) {
+    h += 360.0;
+  }
+  const double j = jstar / (1 - (jstar - 100) * 0.007);
+  return CamFromJchAndViewingConditions(j, c, h, viewing_conditions);
+}
+
+Cam CamFromIntAndViewingConditions(
+    Argb argb, const ViewingConditions &viewing_conditions) {
+  // XYZ from ARGB, inlined.
+  int red = (argb & 0x00ff0000) >> 16;
+  int green = (argb & 0x0000ff00) >> 8;
+  int blue = (argb & 0x000000ff);
+  double red_l = Linearized(red);
+  double green_l = Linearized(green);
+  double blue_l = Linearized(blue);
+  double x = 0.41233895 * red_l + 0.35762064 * green_l + 0.18051042 * blue_l;
+  double y = 0.2126 * red_l + 0.7152 * green_l + 0.0722 * blue_l;
+  double z = 0.01932141 * red_l + 0.11916382 * green_l + 0.95034478 * blue_l;
+
+  // Convert XYZ to 'cone'/'rgb' responses
+  double r_c = 0.401288 * x + 0.650173 * y - 0.051461 * z;
+  double g_c = -0.250268 * x + 1.204414 * y + 0.045854 * z;
+  double b_c = -0.002079 * x + 0.048952 * y + 0.953127 * z;
+
+  // Discount illuminant.
+  double r_d = viewing_conditions.rgb_d[0] * r_c;
+  double g_d = viewing_conditions.rgb_d[1] * g_c;
+  double b_d = viewing_conditions.rgb_d[2] * b_c;
+
+  // Chromatic adaptation.
+  double r_af = pow(viewing_conditions.fl * fabs(r_d) / 100.0, 0.42);
+  double g_af = pow(viewing_conditions.fl * fabs(g_d) / 100.0, 0.42);
+  double b_af = pow(viewing_conditions.fl * fabs(b_d) / 100.0, 0.42);
+  double r_a = Signum(r_d) * 400.0 * r_af / (r_af + 27.13);
+  double g_a = Signum(g_d) * 400.0 * g_af / (g_af + 27.13);
+  double b_a = Signum(b_d) * 400.0 * b_af / (b_af + 27.13);
+
+  // Redness-greenness
+  double a = (11.0 * r_a + -12.0 * g_a + b_a) / 11.0;
+  double b = (r_a + g_a - 2.0 * b_a) / 9.0;
+  double u = (20.0 * r_a + 20.0 * g_a + 21.0 * b_a) / 20.0;
+  double p2 = (40.0 * r_a + 20.0 * g_a + b_a) / 20.0;
+
+  double radians = atan2(b, a);
+  double degrees = radians * 180.0 / kPi;
+  double hue = SanitizeDegreesDouble(degrees);
+  double hue_radians = hue * kPi / 180.0;
+  double ac = p2 * viewing_conditions.nbb;
+
+  double j = 100.0 * pow(ac / viewing_conditions.aw,
+                         viewing_conditions.c * viewing_conditions.z);
+  double q = (4.0 / viewing_conditions.c) * sqrt(j / 100.0) *
+             (viewing_conditions.aw + 4.0) * viewing_conditions.fl_root;
+  double hue_prime = hue < 20.14 ? hue + 360 : hue;
+  double e_hue = 0.25 * (cos(hue_prime * kPi / 180.0 + 2.0) + 3.8);
+  double p1 =
+      50000.0 / 13.0 * e_hue * viewing_conditions.n_c * viewing_conditions.ncb;
+  double t = p1 * sqrt(a * a + b * b) / (u + 0.305);
+  double alpha =
+      pow(t, 0.9) *
+      pow(1.64 - pow(0.29, viewing_conditions.background_y_to_white_point_y),
+          0.73);
+  double c = alpha * sqrt(j / 100.0);
+  double m = c * viewing_conditions.fl_root;
+  double s = 50.0 * sqrt((alpha * viewing_conditions.c) /
+                         (viewing_conditions.aw + 4.0));
+  double jstar = (1.0 + 100.0 * 0.007) * j / (1.0 + 0.007 * j);
+  double mstar = 1.0 / 0.0228 * log(1.0 + 0.0228 * m);
+  double astar = mstar * cos(hue_radians);
+  double bstar = mstar * sin(hue_radians);
+  return {hue, c, j, q, m, s, jstar, astar, bstar};
+}
+
+Cam CamFromInt(Argb argb) {
+  return CamFromIntAndViewingConditions(argb, kDefaultViewingConditions);
+}
+
+Argb IntFromCamAndViewingConditions(Cam cam,
+                                    ViewingConditions viewing_conditions) {
+  double alpha = (cam.chroma == 0.0 || cam.j == 0.0)
+                     ? 0.0
+                     : cam.chroma / sqrt(cam.j / 100.0);
+  double t = pow(
+      alpha / pow(1.64 - pow(0.29,
+                             viewing_conditions.background_y_to_white_point_y),
+                  0.73),
+      1.0 / 0.9);
+  double h_rad = cam.hue * kPi / 180.0;
+  double e_hue = 0.25 * (cos(h_rad + 2.0) + 3.8);
+  double ac =
+      viewing_conditions.aw *
+      pow(cam.j / 100.0, 1.0 / viewing_conditions.c / viewing_conditions.z);
+  double p1 = e_hue * (50000.0 / 13.0) * viewing_conditions.n_c *
+              viewing_conditions.ncb;
+  double p2 = ac / viewing_conditions.nbb;
+  double h_sin = sin(h_rad);
+  double h_cos = cos(h_rad);
+  double gamma = 23.0 * (p2 + 0.305) * t /
+                 (23.0 * p1 + 11.0 * t * h_cos + 108.0 * t * h_sin);
+  double a = gamma * h_cos;
+  double b = gamma * h_sin;
+  double r_a = (460.0 * p2 + 451.0 * a + 288.0 * b) / 1403.0;
+  double g_a = (460.0 * p2 - 891.0 * a - 261.0 * b) / 1403.0;
+  double b_a = (460.0 * p2 - 220.0 * a - 6300.0 * b) / 1403.0;
+
+  double r_c_base = fmax(0, (27.13 * fabs(r_a)) / (400.0 - fabs(r_a)));
+  double r_c =
+      Signum(r_a) * (100.0 / viewing_conditions.fl) * pow(r_c_base, 1.0 / 0.42);
+  double g_c_base = fmax(0, (27.13 * fabs(g_a)) / (400.0 - fabs(g_a)));
+  double g_c =
+      Signum(g_a) * (100.0 / viewing_conditions.fl) * pow(g_c_base, 1.0 / 0.42);
+  double b_c_base = fmax(0, (27.13 * fabs(b_a)) / (400.0 - fabs(b_a)));
+  double b_c =
+      Signum(b_a) * (100.0 / viewing_conditions.fl) * pow(b_c_base, 1.0 / 0.42);
+  double r_x = r_c / viewing_conditions.rgb_d[0];
+  double g_x = g_c / viewing_conditions.rgb_d[1];
+  double b_x = b_c / viewing_conditions.rgb_d[2];
+  double x = 1.86206786 * r_x - 1.01125463 * g_x + 0.14918677 * b_x;
+  double y = 0.38752654 * r_x + 0.62144744 * g_x - 0.00897398 * b_x;
+  double z = -0.01584150 * r_x - 0.03412294 * g_x + 1.04996444 * b_x;
+
+  // intFromXyz
+  double r_l = 3.2406 * x - 1.5372 * y - 0.4986 * z;
+  double g_l = -0.9689 * x + 1.8758 * y + 0.0415 * z;
+  double b_l = 0.0557 * x - 0.2040 * y + 1.0570 * z;
+
+  int red = Delinearized(r_l);
+  int green = Delinearized(g_l);
+  int blue = Delinearized(b_l);
+
+  return ArgbFromRgb(red, green, blue);
+}
+
+Argb IntFromCam(Cam cam) {
+  return IntFromCamAndViewingConditions(cam, kDefaultViewingConditions);
+}
+
+Cam CamFromJchAndViewingConditions(double j, double c, double h,
+                                   ViewingConditions viewing_conditions) {
+  double q = (4.0 / viewing_conditions.c) * sqrt(j / 100.0) *
+             (viewing_conditions.aw + 4.0) * (viewing_conditions.fl_root);
+  double m = c * viewing_conditions.fl_root;
+  double alpha = c / sqrt(j / 100.0);
+  double s = 50.0 * sqrt((alpha * viewing_conditions.c) /
+                         (viewing_conditions.aw + 4.0));
+  double hue_radians = h * kPi / 180.0;
+  double jstar = (1.0 + 100.0 * 0.007) * j / (1.0 + 0.007 * j);
+  double mstar = 1.0 / 0.0228 * log(1.0 + 0.0228 * m);
+  double astar = mstar * cos(hue_radians);
+  double bstar = mstar * sin(hue_radians);
+  return {h, c, j, q, m, s, jstar, astar, bstar};
+}
+
+double CamDistance(Cam a, Cam b) {
+  double d_j = a.jstar - b.jstar;
+  double d_a = a.astar - b.astar;
+  double d_b = a.bstar - b.bstar;
+  double d_e_prime = sqrt(d_j * d_j + d_a * d_a + d_b * d_b);
+  double d_e = 1.41 * pow(d_e_prime, 0.63);
+  return d_e;
+}
+
+Argb IntFromHcl(double hue, double chroma, double lstar) {
+  return SolveToInt(hue, chroma, lstar);
+}
+
+Cam CamFromXyzAndViewingConditions(
+    double x, double y, double z, const ViewingConditions &viewing_conditions) {
+  // Convert XYZ to 'cone'/'rgb' responses
+  double r_c = 0.401288 * x + 0.650173 * y - 0.051461 * z;
+  double g_c = -0.250268 * x + 1.204414 * y + 0.045854 * z;
+  double b_c = -0.002079 * x + 0.048952 * y + 0.953127 * z;
+
+  // Discount illuminant.
+  double r_d = viewing_conditions.rgb_d[0] * r_c;
+  double g_d = viewing_conditions.rgb_d[1] * g_c;
+  double b_d = viewing_conditions.rgb_d[2] * b_c;
+
+  // Chromatic adaptation.
+  double r_af = pow(viewing_conditions.fl * fabs(r_d) / 100.0, 0.42);
+  double g_af = pow(viewing_conditions.fl * fabs(g_d) / 100.0, 0.42);
+  double b_af = pow(viewing_conditions.fl * fabs(b_d) / 100.0, 0.42);
+  double r_a = Signum(r_d) * 400.0 * r_af / (r_af + 27.13);
+  double g_a = Signum(g_d) * 400.0 * g_af / (g_af + 27.13);
+  double b_a = Signum(b_d) * 400.0 * b_af / (b_af + 27.13);
+
+  // Redness-greenness
+  double a = (11.0 * r_a + -12.0 * g_a + b_a) / 11.0;
+  double b = (r_a + g_a - 2.0 * b_a) / 9.0;
+  double u = (20.0 * r_a + 20.0 * g_a + 21.0 * b_a) / 20.0;
+  double p2 = (40.0 * r_a + 20.0 * g_a + b_a) / 20.0;
+
+  double radians = atan2(b, a);
+  double degrees = radians * 180.0 / kPi;
+  double hue = SanitizeDegreesDouble(degrees);
+  double hue_radians = hue * kPi / 180.0;
+  double ac = p2 * viewing_conditions.nbb;
+
+  double j = 100.0 * pow(ac / viewing_conditions.aw,
+                         viewing_conditions.c * viewing_conditions.z);
+  double q = (4.0 / viewing_conditions.c) * sqrt(j / 100.0) *
+             (viewing_conditions.aw + 4.0) * viewing_conditions.fl_root;
+  double hue_prime = hue < 20.14 ? hue + 360 : hue;
+  double e_hue = 0.25 * (cos(hue_prime * kPi / 180.0 + 2.0) + 3.8);
+  double p1 =
+      50000.0 / 13.0 * e_hue * viewing_conditions.n_c * viewing_conditions.ncb;
+  double t = p1 * sqrt(a * a + b * b) / (u + 0.305);
+  double alpha =
+      pow(t, 0.9) *
+      pow(1.64 - pow(0.29, viewing_conditions.background_y_to_white_point_y),
+          0.73);
+  double c = alpha * sqrt(j / 100.0);
+  double m = c * viewing_conditions.fl_root;
+  double s = 50.0 * sqrt((alpha * viewing_conditions.c) /
+                         (viewing_conditions.aw + 4.0));
+  double jstar = (1.0 + 100.0 * 0.007) * j / (1.0 + 0.007 * j);
+  double mstar = 1.0 / 0.0228 * log(1.0 + 0.0228 * m);
+  double astar = mstar * cos(hue_radians);
+  double bstar = mstar * sin(hue_radians);
+  return {hue, c, j, q, m, s, jstar, astar, bstar};
+}
+
+}  // namespace material_color_utilities

third_party/material_color_utilities/cpp/cam/cam.h

@@ -0,0 +1,53 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CPP_CAM_CAM_H_
+#define CPP_CAM_CAM_H_
+
+#include "cpp/cam/viewing_conditions.h"
+#include "cpp/utils/utils.h"
+
+namespace material_color_utilities {
+
+struct Cam {
+  double hue = 0.0;
+  double chroma = 0.0;
+  double j = 0.0;
+  double q = 0.0;
+  double m = 0.0;
+  double s = 0.0;
+
+  double jstar = 0.0;
+  double astar = 0.0;
+  double bstar = 0.0;
+};
+
+Cam CamFromInt(Argb argb);
+Cam CamFromIntAndViewingConditions(Argb argb,
+                                   const ViewingConditions &viewing_conditions);
+Argb IntFromHcl(double hue, double chroma, double lstar);
+Argb IntFromCam(Cam cam);
+Cam CamFromUcsAndViewingConditions(double jstar, double astar, double bstar,
+                                   const ViewingConditions &viewing_conditions);
+/**
+ * Given color expressed in the XYZ color space and viewed
+ * in [viewingConditions], converts the color to CAM16.
+ */
+Cam CamFromXyzAndViewingConditions(double x, double y, double z,
+                                   const ViewingConditions &viewing_conditions);
+
+}  // namespace material_color_utilities
+#endif  // CPP_CAM_CAM_H_

third_party/material_color_utilities/cpp/cam/hct.cc

@@ -0,0 +1,57 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "cpp/cam/hct.h"
+
+#include "cpp/cam/hct_solver.h"
+#include "cpp/utils/utils.h"
+
+namespace material_color_utilities {
+Hct::Hct(double hue, double chroma, double tone) {
+  SetInternalState(SolveToInt(hue, chroma, tone));
+}
+
+Hct::Hct(Argb argb) { SetInternalState(argb); }
+
+double Hct::get_hue() const { return hue_; }
+
+double Hct::get_chroma() const { return chroma_; }
+
+double Hct::get_tone() const { return tone_; }
+
+Argb Hct::ToInt() const { return argb_; }
+
+void Hct::set_hue(double new_hue) {
+  SetInternalState(SolveToInt(new_hue, chroma_, tone_));
+}
+
+void Hct::set_chroma(double new_chroma) {
+  SetInternalState(SolveToInt(hue_, new_chroma, tone_));
+}
+
+void Hct::set_tone(double new_tone) {
+  SetInternalState(SolveToInt(hue_, chroma_, new_tone));
+}
+
+void Hct::SetInternalState(Argb argb) {
+  argb_ = argb;
+  Cam cam = CamFromInt(argb);
+  hue_ = cam.hue;
+  chroma_ = cam.chroma;
+  tone_ = LstarFromArgb(argb);
+}
+
+}  // namespace material_color_utilities

third_party/material_color_utilities/cpp/cam/hct.h

@@ -0,0 +1,137 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CPP_CAM_HCT_H_
+#define CPP_CAM_HCT_H_
+
+#include "cpp/utils/utils.h"
+
+namespace material_color_utilities {
+
+/**
+ * HCT: hue, chroma, and tone.
+ *
+ * A color system built using CAM16 hue and chroma, and L* (lightness) from
+ * the L*a*b* color space, providing a perceptually accurate
+ * color measurement system that can also accurately render what colors
+ * will appear as in different lighting environments.
+ *
+ * Using L* creates a link between the color system, contrast, and thus
+ * accessibility. Contrast ratio depends on relative luminance, or Y in the XYZ
+ * color space. L*, or perceptual luminance can be calculated from Y.
+ *
+ * Unlike Y, L* is linear to human perception, allowing trivial creation of
+ * accurate color tones.
+ *
+ * Unlike contrast ratio, measuring contrast in L* is linear, and simple to
+ * calculate. A difference of 40 in HCT tone guarantees a contrast ratio >= 3.0,
+ * and a difference of 50 guarantees a contrast ratio >= 4.5.
+ */
+class Hct {
+ public:
+  /**
+   * Creates an HCT color from hue, chroma, and tone.
+   *
+   * @param hue 0 <= hue < 360; invalid values are corrected.
+   * @param chroma >= 0; the maximum value of chroma depends on the hue
+   * and tone. May be lower than the requested chroma.
+   * @param tone 0 <= tone <= 100; invalid values are corrected.
+   * @return HCT representation of a color in default viewing conditions.
+   */
+  Hct(double hue, double chroma, double tone);
+
+  /**
+   * Creates an HCT color from a color.
+   *
+   * @param argb ARGB representation of a color.
+   * @return HCT representation of a color in default viewing conditions
+   */
+  explicit Hct(Argb argb);
+
+  /**
+   * Returns the hue of the color.
+   *
+   * @return hue of the color, in degrees.
+   */
+  double get_hue() const;
+
+  /**
+   * Returns the chroma of the color.
+   *
+   * @return chroma of the color.
+   */
+  double get_chroma() const;
+
+  /**
+   * Returns the tone of the color.
+   *
+   * @return tone of the color, satisfying 0 <= tone <= 100.
+   */
+  double get_tone() const;
+
+  /**
+   * Returns the color in ARGB format.
+   *
+   * @return an integer, representing the color in ARGB format.
+   */
+  Argb ToInt() const;
+
+  /**
+   * Sets the hue of this color. Chroma may decrease because chroma has a
+   * different maximum for any given hue and tone.
+   *
+   * @param new_hue 0 <= new_hue < 360; invalid values are corrected.
+   */
+  void set_hue(double new_hue);
+
+  /**
+   * Sets the chroma of this color. Chroma may decrease because chroma has a
+   * different maximum for any given hue and tone.
+   *
+   * @param new_chroma 0 <= new_chroma < ?
+   */
+  void set_chroma(double new_chroma);
+
+  /**
+   * Sets the tone of this color. Chroma may decrease because chroma has a
+   * different maximum for any given hue and tone.
+   *
+   * @param new_tone 0 <= new_tone <= 100; invalid valids are corrected.
+   */
+  void set_tone(double new_tone);
+
+  /**
+   * For using HCT as a key in a ordered map.
+   */
+  bool operator<(const Hct& a) const { return hue_ < a.hue_; }
+
+ private:
+  /**
+   * Sets the Hct object to represent an sRGB color.
+   *
+   * @param argb the new color as an integer in ARGB format.
+   */
+  void SetInternalState(Argb argb);
+
+  double hue_ = 0.0;
+  double chroma_ = 0.0;
+  double tone_ = 0.0;
+  Argb argb_ = 0;
+};
+
+}  // namespace material_color_utilities
+
+#endif  // CPP_CAM_HCT_H_

third_party/material_color_utilities/cpp/cam/hct_solver.cc

@@ -0,0 +1,526 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "cpp/cam/hct_solver.h"
+
+#include <math.h>
+
+#include "cpp/cam/viewing_conditions.h"
+#include "cpp/utils/utils.h"
+
+namespace material_color_utilities {
+
+constexpr double kScaledDiscountFromLinrgb[3][3] = {
+    {
+        0.001200833568784504,
+        0.002389694492170889,
+        0.0002795742885861124,
+    },
+    {
+        0.0005891086651375999,
+        0.0029785502573438758,
+        0.0003270666104008398,
+    },
+    {
+        0.00010146692491640572,
+        0.0005364214359186694,
+        0.0032979401770712076,
+    },
+};
+
+constexpr double kLinrgbFromScaledDiscount[3][3] = {
+    {
+        1373.2198709594231,
+        -1100.4251190754821,
+        -7.278681089101213,
+    },
+    {
+        -271.815969077903,
+        559.6580465940733,
+        -32.46047482791194,
+    },
+    {
+        1.9622899599665666,
+        -57.173814538844006,
+        308.7233197812385,
+    },
+};
+
+constexpr double kYFromLinrgb[3] = {0.2126, 0.7152, 0.0722};
+
+constexpr double kCriticalPlanes[255] = {
+    0.015176349177441876, 0.045529047532325624, 0.07588174588720938,
+    0.10623444424209313,  0.13658714259697685,  0.16693984095186062,
+    0.19729253930674434,  0.2276452376616281,   0.2579979360165119,
+    0.28835063437139563,  0.3188300904430532,   0.350925934958123,
+    0.3848314933096426,   0.42057480301049466,  0.458183274052838,
+    0.4976837250274023,   0.5391024159806381,   0.5824650784040898,
+    0.6277969426914107,   0.6751227633498623,   0.7244668422128921,
+    0.775853049866786,    0.829304845476233,    0.8848452951698498,
+    0.942497089126609,    1.0022825574869039,   1.0642236851973577,
+    1.1283421258858297,   1.1946592148522128,   1.2631959812511864,
+    1.3339731595349034,   1.407011200216447,    1.4823302800086415,
+    1.5599503113873272,   1.6398909516233677,   1.7221716113234105,
+    1.8068114625156377,   1.8938294463134073,   1.9832442801866852,
+    2.075074464868551,    2.1693382909216234,   2.2660538449872063,
+    2.36523901573795,     2.4669114995532007,   2.5710888059345764,
+    2.6777882626779785,   2.7870270208169257,   2.898822059350997,
+    3.0131901897720907,   3.1301480604002863,   3.2497121605402226,
+    3.3718988244681087,   3.4967242352587946,   3.624204428461639,
+    3.754355295633311,    3.887192587735158,    4.022731918402185,
+    4.160988767090289,    4.301978482107941,    4.445716283538092,
+    4.592217266055746,    4.741496401646282,    4.893568542229298,
+    5.048448422192488,    5.20615066083972,     5.3666897647573375,
+    5.5300801301023865,   5.696336044816294,    5.865471690767354,
+    6.037501145825082,    6.212438385869475,    6.390297286737924,
+    6.571091626112461,    6.7548350853498045,   6.941541251256611,
+    7.131223617812143,    7.323895587840543,    7.5195704746346665,
+    7.7182615035334345,   7.919981813454504,    8.124744458384042,
+    8.332562408825165,    8.543448553206703,    8.757415699253682,
+    8.974476575321063,    9.194643831691977,    9.417930041841839,
+    9.644347703669503,    9.873909240696694,    10.106627003236781,
+    10.342513269534024,   10.58158024687427,    10.8238400726681,
+    11.069304815507364,   11.317986476196008,   11.569896988756009,
+    11.825048221409341,   12.083451977536606,   12.345119996613247,
+    12.610063955123938,   12.878295467455942,   13.149826086772048,
+    13.42466730586372,    13.702830557985108,   13.984327217668513,
+    14.269168601521828,   14.55736596900856,    14.848930523210871,
+    15.143873411576273,   15.44220572664832,    15.743938506781891,
+    16.04908273684337,    16.35764934889634,    16.66964922287304,
+    16.985093187232053,   17.30399201960269,    17.62635644741625,
+    17.95219714852476,    18.281524751807332,   18.614349837764564,
+    18.95068293910138,    19.290534541298456,   19.633915083172692,
+    19.98083495742689,    20.331304511189067,   20.685334046541502,
+    21.042933821039977,   21.404114048223256,   21.76888489811322,
+    22.137256497705877,   22.50923893145328,    22.884842241736916,
+    23.264076429332462,   23.6469514538663,     24.033477234264016,
+    24.42366364919083,    24.817520537484558,   25.21505769858089,
+    25.61628489293138,    26.021211842414342,   26.429848230738664,
+    26.842203703840827,   27.258287870275353,   27.678110301598522,
+    28.10168053274597,    28.529008062403893,   28.96010235337422,
+    29.39497283293396,    29.83362889318845,    30.276079891419332,
+    30.722335150426627,   31.172403958865512,   31.62629557157785,
+    32.08401920991837,    32.54558406207592,    33.010999283389665,
+    33.4802739966603,     33.953417292456834,   34.430438229418264,
+    34.911345834551085,   35.39614910352207,    35.88485700094671,
+    36.37747846067349,    36.87402238606382,    37.37449765026789,
+    37.87891309649659,    38.38727753828926,    38.89959975977785,
+    39.41588851594697,    39.93615253289054,    40.460400508064545,
+    40.98864111053629,    41.520882981230194,   42.05713473317016,
+    42.597404951718396,   43.141702194811224,   43.6900349931913,
+    44.24241185063697,    44.798841244188324,   45.35933162437017,
+    45.92389141541209,    46.49252901546552,    47.065252796817916,
+    47.64207110610409,    48.22299226451468,    48.808024568002054,
+    49.3971762874833,     49.9904556690408,     50.587870934119984,
+    51.189430279724725,   51.79514187861014,    52.40501387947288,
+    53.0190544071392,     53.637271562750364,   54.259673423945976,
+    54.88626804504493,    55.517063457223934,   56.15206766869424,
+    56.79128866487574,    57.43473440856916,    58.08241284012621,
+    58.734331877617365,   59.39049941699807,    60.05092333227251,
+    60.715611475655585,   61.38457167773311,    62.057811747619894,
+    62.7353394731159,     63.417162620860914,   64.10328893648692,
+    64.79372614476921,    65.48848194977529,    66.18756403501224,
+    66.89098006357258,    67.59873767827808,    68.31084450182222,
+    69.02730813691093,    69.74813616640164,    70.47333615344107,
+    71.20291564160104,    71.93688215501312,    72.67524319850172,
+    73.41800625771542,    74.16517879925733,    74.9167682708136,
+    75.67278210128072,    76.43322770089146,    77.1981124613393,
+    77.96744375590167,    78.74122893956174,    79.51947534912904,
+    80.30219030335869,    81.08938110306934,    81.88105503125999,
+    82.67721935322541,    83.4778813166706,     84.28304815182372,
+    85.09272707154808,    85.90692527145302,    86.72564993000343,
+    87.54890820862819,    88.3767072518277,     89.2090541872801,
+    90.04595612594655,    90.88742016217518,    91.73345337380438,
+    92.58406282226491,    93.43925555268066,    94.29903859396902,
+    95.16341895893969,    96.03240364439274,    96.9059996312159,
+    97.78421388448044,    98.6670533535366,     99.55452497210776,
+};
+
+/**
+ * Sanitizes a small enough angle in radians.
+ *
+ * @param angle An angle in radians; must not deviate too much from 0.
+ * @return A coterminal angle between 0 and 2pi.
+ */
+double SanitizeRadians(double angle) { return fmod(angle + kPi * 8, kPi * 2); }
+
+/**
+ * Delinearizes an RGB component, returning a floating-point number.
+ *
+ * @param rgb_component 0.0 <= rgb_component <= 100.0, represents linear R/G/B
+ * channel
+ * @return 0.0 <= output <= 255.0, color channel converted to regular RGB space
+ */
+double TrueDelinearized(double rgb_component) {
+  double normalized = rgb_component / 100.0;
+  double delinearized = 0.0;
+  if (normalized <= 0.0031308) {
+    delinearized = normalized * 12.92;
+  } else {
+    delinearized = 1.055 * pow(normalized, 1.0 / 2.4) - 0.055;
+  }
+  return delinearized * 255.0;
+}
+
+double ChromaticAdaptation(double component) {
+  double af = pow(abs(component), 0.42);
+  return Signum(component) * 400.0 * af / (af + 27.13);
+}
+
+/**
+ * Returns the hue of a linear RGB color in CAM16.
+ *
+ * @param linrgb The linear RGB coordinates of a color.
+ * @return The hue of the color in CAM16, in radians.
+ */
+double HueOf(Vec3 linrgb) {
+  Vec3 scaledDiscount = MatrixMultiply(linrgb, kScaledDiscountFromLinrgb);
+  double r_a = ChromaticAdaptation(scaledDiscount.a);
+  double g_a = ChromaticAdaptation(scaledDiscount.b);
+  double b_a = ChromaticAdaptation(scaledDiscount.c);
+  // redness-greenness
+  double a = (11.0 * r_a + -12.0 * g_a + b_a) / 11.0;
+  // yellowness-blueness
+  double b = (r_a + g_a - 2.0 * b_a) / 9.0;
+  return atan2(b, a);
+}
+
+bool AreInCyclicOrder(double a, double b, double c) {
+  double delta_a_b = SanitizeRadians(b - a);
+  double delta_a_c = SanitizeRadians(c - a);
+  return delta_a_b < delta_a_c;
+}
+
+/**
+ * Solves the lerp equation.
+ *
+ * @param source The starting number.
+ * @param mid The number in the middle.
+ * @param target The ending number.
+ * @return A number t such that lerp(source, target, t) = mid.
+ */
+double Intercept(double source, double mid, double target) {
+  return (mid - source) / (target - source);
+}
+
+Vec3 LerpPoint(Vec3 source, double t, Vec3 target) {
+  return (Vec3){
+      source.a + (target.a - source.a) * t,
+      source.b + (target.b - source.b) * t,
+      source.c + (target.c - source.c) * t,
+  };
+}
+
+double GetAxis(Vec3 vector, int axis) {
+  switch (axis) {
+    case 0:
+      return vector.a;
+    case 1:
+      return vector.b;
+    case 2:
+      return vector.c;
+    default:
+      return -1.0;
+  }
+}
+
+/**
+ * Intersects a segment with a plane.
+ *
+ * @param source The coordinates of point A.
+ * @param coordinate The R-, G-, or B-coordinate of the plane.
+ * @param target The coordinates of point B.
+ * @param axis The axis the plane is perpendicular with. (0: R, 1: G, 2: B)
+ * @return The intersection point of the segment AB with the plane R=coordinate,
+ * G=coordinate, or B=coordinate
+ */
+Vec3 SetCoordinate(Vec3 source, double coordinate, Vec3 target, int axis) {
+  double t =
+      Intercept(GetAxis(source, axis), coordinate, GetAxis(target, axis));
+  return LerpPoint(source, t, target);
+}
+
+bool IsBounded(double x) { return 0.0 <= x && x <= 100.0; }
+
+/**
+ * Returns the nth possible vertex of the polygonal intersection.
+ *
+ * @param y The Y value of the plane.
+ * @param n The zero-based index of the point. 0 <= n <= 11.
+ * @return The nth possible vertex of the polygonal intersection of the y plane
+ * and the RGB cube, in linear RGB coordinates, if it exists. If this possible
+ * vertex lies outside of the cube,
+ *     [-1.0, -1.0, -1.0] is returned.
+ */
+Vec3 NthVertex(double y, int n) {
+  double k_r = kYFromLinrgb[0];
+  double k_g = kYFromLinrgb[1];
+  double k_b = kYFromLinrgb[2];
+  double coord_a = n % 4 <= 1 ? 0.0 : 100.0;
+  double coord_b = n % 2 == 0 ? 0.0 : 100.0;
+  if (n < 4) {
+    double g = coord_a;
+    double b = coord_b;
+    double r = (y - g * k_g - b * k_b) / k_r;
+    if (IsBounded(r)) {
+      return (Vec3){r, g, b};
+    } else {
+      return (Vec3){-1.0, -1.0, -1.0};
+    }
+  } else if (n < 8) {
+    double b = coord_a;
+    double r = coord_b;
+    double g = (y - r * k_r - b * k_b) / k_g;
+    if (IsBounded(g)) {
+      return (Vec3){r, g, b};
+    } else {
+      return (Vec3){-1.0, -1.0, -1.0};
+    }
+  } else {
+    double r = coord_a;
+    double g = coord_b;
+    double b = (y - r * k_r - g * k_g) / k_b;
+    if (IsBounded(b)) {
+      return (Vec3){r, g, b};
+    } else {
+      return (Vec3){-1.0, -1.0, -1.0};
+    }
+  }
+}
+
+/**
+ * Finds the segment containing the desired color.
+ *
+ * @param y The Y value of the color.
+ * @param target_hue The hue of the color.
+ * @return A list of two sets of linear RGB coordinates, each corresponding to
+ * an endpoint of the segment containing the desired color.
+ */
+void BisectToSegment(double y, double target_hue, Vec3 out[2]) {
+  Vec3 left = (Vec3){-1.0, -1.0, -1.0};
+  Vec3 right = left;
+  double left_hue = 0.0;
+  double right_hue = 0.0;
+  bool initialized = false;
+  bool uncut = true;
+  for (int n = 0; n < 12; n++) {
+    Vec3 mid = NthVertex(y, n);
+    if (mid.a < 0) {
+      continue;
+    }
+    double mid_hue = HueOf(mid);
+    if (!initialized) {
+      left = mid;
+      right = mid;
+      left_hue = mid_hue;
+      right_hue = mid_hue;
+      initialized = true;
+      continue;
+    }
+    if (uncut || AreInCyclicOrder(left_hue, mid_hue, right_hue)) {
+      uncut = false;
+      if (AreInCyclicOrder(left_hue, target_hue, mid_hue)) {
+        right = mid;
+        right_hue = mid_hue;
+      } else {
+        left = mid;
+        left_hue = mid_hue;
+      }
+    }
+  }
+  out[0] = left;
+  out[1] = right;
+}
+
+Vec3 Midpoint(Vec3 a, Vec3 b) {
+  return (Vec3){
+      (a.a + b.a) / 2,
+      (a.b + b.b) / 2,
+      (a.c + b.c) / 2,
+  };
+}
+
+int CriticalPlaneBelow(double x) { return (int)floor(x - 0.5); }
+
+int CriticalPlaneAbove(double x) { return (int)ceil(x - 0.5); }
+
+/**
+ * Finds a color with the given Y and hue on the boundary of the cube.
+ *
+ * @param y The Y value of the color.
+ * @param target_hue The hue of the color.
+ * @return The desired color, in linear RGB coordinates.
+ */
+Vec3 BisectToLimit(double y, double target_hue) {
+  Vec3 segment[2];
+  BisectToSegment(y, target_hue, segment);
+  Vec3 left = segment[0];
+  double left_hue = HueOf(left);
+  Vec3 right = segment[1];
+  for (int axis = 0; axis < 3; axis++) {
+    if (GetAxis(left, axis) != GetAxis(right, axis)) {
+      int l_plane = -1;
+      int r_plane = 255;
+      if (GetAxis(left, axis) < GetAxis(right, axis)) {
+        l_plane = CriticalPlaneBelow(TrueDelinearized(GetAxis(left, axis)));
+        r_plane = CriticalPlaneAbove(TrueDelinearized(GetAxis(right, axis)));
+      } else {
+        l_plane = CriticalPlaneAbove(TrueDelinearized(GetAxis(left, axis)));
+        r_plane = CriticalPlaneBelow(TrueDelinearized(GetAxis(right, axis)));
+      }
+      for (int i = 0; i < 8; i++) {
+        if (abs(r_plane - l_plane) <= 1) {
+          break;
+        } else {
+          int m_plane = (int)floor((l_plane + r_plane) / 2.0);
+          double mid_plane_coordinate = kCriticalPlanes[m_plane];
+          Vec3 mid = SetCoordinate(left, mid_plane_coordinate, right, axis);
+          double mid_hue = HueOf(mid);
+          if (AreInCyclicOrder(left_hue, target_hue, mid_hue)) {
+            right = mid;
+            r_plane = m_plane;
+          } else {
+            left = mid;
+            left_hue = mid_hue;
+            l_plane = m_plane;
+          }
+        }
+      }
+    }
+  }
+  return Midpoint(left, right);
+}
+
+double InverseChromaticAdaptation(double adapted) {
+  double adapted_abs = abs(adapted);
+  double base = fmax(0, 27.13 * adapted_abs / (400.0 - adapted_abs));
+  return Signum(adapted) * pow(base, 1.0 / 0.42);
+}
+
+/**
+ * Finds a color with the given hue, chroma, and Y.
+ *
+ * @param hue_radians The desired hue in radians.
+ * @param chroma The desired chroma.
+ * @param y The desired Y.
+ * @return The desired color as a hexadecimal integer, if found; 0 otherwise.
+ */
+Argb FindResultByJ(double hue_radians, double chroma, double y) {
+  // Initial estimate of j.
+  double j = sqrt(y) * 11.0;
+  // ===========================================================
+  // Operations inlined from Cam16 to avoid repeated calculation
+  // ===========================================================
+  ViewingConditions viewing_conditions = kDefaultViewingConditions;
+  double t_inner_coeff =
+      1 /
+      pow(1.64 - pow(0.29, viewing_conditions.background_y_to_white_point_y),
+          0.73);
+  double e_hue = 0.25 * (cos(hue_radians + 2.0) + 3.8);
+  double p1 = e_hue * (50000.0 / 13.0) * viewing_conditions.n_c *
+              viewing_conditions.ncb;
+  double h_sin = sin(hue_radians);
+  double h_cos = cos(hue_radians);
+  for (int iteration_round = 0; iteration_round < 5; iteration_round++) {
+    // ===========================================================
+    // Operations inlined from Cam16 to avoid repeated calculation
+    // ===========================================================
+    double j_normalized = j / 100.0;
+    double alpha =
+        chroma == 0.0 || j == 0.0 ? 0.0 : chroma / sqrt(j_normalized);
+    double t = pow(alpha * t_inner_coeff, 1.0 / 0.9);
+    double ac =
+        viewing_conditions.aw *
+        pow(j_normalized, 1.0 / viewing_conditions.c / viewing_conditions.z);
+    double p2 = ac / viewing_conditions.nbb;
+    double gamma = 23.0 * (p2 + 0.305) * t /
+                   (23.0 * p1 + 11 * t * h_cos + 108.0 * t * h_sin);
+    double a = gamma * h_cos;
+    double b = gamma * h_sin;
+    double r_a = (460.0 * p2 + 451.0 * a + 288.0 * b) / 1403.0;
+    double g_a = (460.0 * p2 - 891.0 * a - 261.0 * b) / 1403.0;
+    double b_a = (460.0 * p2 - 220.0 * a - 6300.0 * b) / 1403.0;
+    double r_c_scaled = InverseChromaticAdaptation(r_a);
+    double g_c_scaled = InverseChromaticAdaptation(g_a);
+    double b_c_scaled = InverseChromaticAdaptation(b_a);
+    Vec3 scaled = (Vec3){r_c_scaled, g_c_scaled, b_c_scaled};
+    Vec3 linrgb = MatrixMultiply(scaled, kLinrgbFromScaledDiscount);
+    // ===========================================================
+    // Operations inlined from Cam16 to avoid repeated calculation
+    // ===========================================================
+    if (linrgb.a < 0 || linrgb.b < 0 || linrgb.c < 0) {
+      return 0;
+    }
+    double k_r = kYFromLinrgb[0];
+    double k_g = kYFromLinrgb[1];
+    double k_b = kYFromLinrgb[2];
+    double fnj = k_r * linrgb.a + k_g * linrgb.b + k_b * linrgb.c;
+    if (fnj <= 0) {
+      return 0;
+    }
+    if (iteration_round == 4 || abs(fnj - y) < 0.002) {
+      if (linrgb.a > 100.01 || linrgb.b > 100.01 || linrgb.c > 100.01) {
+        return 0;
+      }
+      return ArgbFromLinrgb(linrgb);
+    }
+    // Iterates with Newton method,
+    // Using 2 * fn(j) / j as the approximation of fn'(j)
+    j = j - (fnj - y) * j / (2 * fnj);
+  }
+  return 0;
+}
+
+/**
+ * Finds an sRGB color with the given hue, chroma, and L*, if possible.
+ *
+ * @param hue_degrees The desired hue, in degrees.
+ * @param chroma The desired chroma.
+ * @param lstar The desired L*.
+ * @return A hexadecimal representing the sRGB color. The color has sufficiently
+ * close hue, chroma, and L* to the desired values, if possible; otherwise, the
+ * hue and L* will be sufficiently close, and chroma will be maximized.
+ */
+Argb SolveToInt(double hue_degrees, double chroma, double lstar) {
+  if (chroma < 0.0001 || lstar < 0.0001 || lstar > 99.9999) {
+    return IntFromLstar(lstar);
+  }
+  hue_degrees = SanitizeDegreesDouble(hue_degrees);
+  double hue_radians = hue_degrees / 180 * kPi;
+  double y = YFromLstar(lstar);
+  Argb exact_answer = FindResultByJ(hue_radians, chroma, y);
+  if (exact_answer != 0) {
+    return exact_answer;
+  }
+  Vec3 linrgb = BisectToLimit(y, hue_radians);
+  return ArgbFromLinrgb(linrgb);
+}
+
+/**
+ * Finds an sRGB color with the given hue, chroma, and L*, if possible.
+ *
+ * @param hue_degrees The desired hue, in degrees.
+ * @param chroma The desired chroma.
+ * @param lstar The desired L*.
+ * @return An CAM16 object representing the sRGB color. The color has
+ * sufficiently close hue, chroma, and L* to the desired values, if possible;
+ * otherwise, the hue and L* will be sufficiently close, and chroma will be
+ * maximized.
+ */
+Cam SolveToCam(double hue_degrees, double chroma, double lstar) {
+  return CamFromInt(SolveToInt(hue_degrees, chroma, lstar));
+}
+}  // namespace material_color_utilities

third_party/material_color_utilities/cpp/cam/hct_solver.h

@@ -0,0 +1,28 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CPP_CAM_HCT_SOLVER_H_
+#define CPP_CAM_HCT_SOLVER_H_
+
+#include "cpp/cam/cam.h"
+
+namespace material_color_utilities {
+
+Argb SolveToInt(double hue_degrees, double chroma, double lstar);
+Cam SolveToCam(double hue_degrees, double chroma, double lstar);
+
+}  // namespace material_color_utilities
+#endif  // CPP_CAM_HCT_SOLVER_H_

third_party/material_color_utilities/cpp/cam/viewing_conditions.cc

@@ -0,0 +1,118 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "cpp/cam/viewing_conditions.h"
+
+#include <math.h>
+#include <stdio.h>
+
+#include "cpp/utils/utils.h"
+
+namespace material_color_utilities {
+
+static double lerp(double start, double stop, double amount) {
+  return (1.0 - amount) * start + amount * stop;
+}
+
+ViewingConditions CreateViewingConditions(const double white_point[3],
+                                          const double adapting_luminance,
+                                          const double background_lstar,
+                                          const double surround,
+                                          const bool discounting_illuminant) {
+  double background_lstar_corrected =
+      (background_lstar < 30.0) ? 30.0 : background_lstar;
+  double rgb_w[3] = {
+      0.401288 * white_point[0] + 0.650173 * white_point[1] -
+          0.051461 * white_point[2],
+      -0.250268 * white_point[0] + 1.204414 * white_point[1] +
+          0.045854 * white_point[2],
+      -0.002079 * white_point[0] + 0.048952 * white_point[1] +
+          0.953127 * white_point[2],
+  };
+  double f = 0.8 + (surround / 10.0);
+  double c = f >= 0.9 ? lerp(0.59, 0.69, (f - 0.9) * 10.0)
+                      : lerp(0.525, 0.59, (f - 0.8) * 10.0);
+  double d = discounting_illuminant
+                 ? 1.0
+                 : f * (1.0 - ((1.0 / 3.6) *
+                               exp((-adapting_luminance - 42.0) / 92.0)));
+  d = d > 1.0 ? 1.0 : d < 0.0 ? 0.0 : d;
+  double nc = f;
+  double rgb_d[3] = {(d * (100.0 / rgb_w[0]) + 1.0 - d),
+                     (d * (100.0 / rgb_w[1]) + 1.0 - d),
+                     (d * (100.0 / rgb_w[2]) + 1.0 - d)};
+
+  double k = 1.0 / (5.0 * adapting_luminance + 1.0);
+  double k4 = k * k * k * k;
+  double k4f = 1.0 - k4;
+  double fl = (k4 * adapting_luminance) +
+              (0.1 * k4f * k4f * pow(5.0 * adapting_luminance, 1.0 / 3.0));
+  double fl_root = pow(fl, 0.25);
+  double n = YFromLstar(background_lstar_corrected) / white_point[1];
+  double z = 1.48 + sqrt(n);
+  double nbb = 0.725 / pow(n, 0.2);
+  double ncb = nbb;
+  double rgb_a_factors[3] = {pow(fl * rgb_d[0] * rgb_w[0] / 100.0, 0.42),
+                             pow(fl * rgb_d[1] * rgb_w[1] / 100.0, 0.42),
+                             pow(fl * rgb_d[2] * rgb_w[2] / 100.0, 0.42)};
+  double rgb_a[3] = {
+      400.0 * rgb_a_factors[0] / (rgb_a_factors[0] + 27.13),
+      400.0 * rgb_a_factors[1] / (rgb_a_factors[1] + 27.13),
+      400.0 * rgb_a_factors[2] / (rgb_a_factors[2] + 27.13),
+  };
+  double aw = (40.0 * rgb_a[0] + 20.0 * rgb_a[1] + rgb_a[2]) / 20.0 * nbb;
+  ViewingConditions viewingConditions = {
+      adapting_luminance,
+      background_lstar_corrected,
+      surround,
+      discounting_illuminant,
+      n,
+      aw,
+      nbb,
+      ncb,
+      c,
+      nc,
+      fl,
+      fl_root,
+      z,
+      {white_point[0], white_point[1], white_point[2]},
+      {rgb_d[0], rgb_d[1], rgb_d[2]},
+  };
+  return viewingConditions;
+}
+
+ViewingConditions DefaultWithBackgroundLstar(const double background_lstar) {
+  return CreateViewingConditions(kWhitePointD65,
+                                 (200.0 / kPi * YFromLstar(50.0) / 100.0),
+                                 background_lstar, 2.0, 0);
+}
+
+void PrintDefaultFrame() {
+  ViewingConditions frame = CreateViewingConditions(
+      kWhitePointD65, (200.0 / kPi * YFromLstar(50.0) / 100.0), 50.0, 2.0, 0);
+  printf(
+      "(Frame){%0.9lf,\n %0.9lf,\n %0.9lf,\n %s\n, %0.9lf,\n "
+      "%0.9lf,\n%0.9lf,\n%0.9lf,\n%0.9lf,\n%0.9lf,\n"
+      "%0.9lf,\n%0.9lf,\n%0.9lf,\n%0.9lf,\n"
+      "%0.9lf,\n%0.9lf\n};",
+      frame.adapting_luminance, frame.background_lstar, frame.surround,
+      frame.discounting_illuminant ? "true" : "false",
+      frame.background_y_to_white_point_y, frame.aw, frame.nbb, frame.ncb,
+      frame.c, frame.n_c, frame.fl, frame.fl_root, frame.z, frame.rgb_d[0],
+      frame.rgb_d[1], frame.rgb_d[2]);
+}
+
+}  // namespace material_color_utilities

third_party/material_color_utilities/cpp/cam/viewing_conditions.h

@@ -0,0 +1,68 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CPP_CAM_VIEWING_CONDITIONS_H_
+#define CPP_CAM_VIEWING_CONDITIONS_H_
+
+namespace material_color_utilities {
+
+struct ViewingConditions {
+  double adapting_luminance = 0.0;
+  double background_lstar = 0.0;
+  double surround = 0.0;
+  bool discounting_illuminant = false;
+  double background_y_to_white_point_y = 0.0;
+  double aw = 0.0;
+  double nbb = 0.0;
+  double ncb = 0.0;
+  double c = 0.0;
+  double n_c = 0.0;
+  double fl = 0.0;
+  double fl_root = 0.0;
+  double z = 0.0;
+
+  double white_point[3] = {0.0, 0.0, 0.0};
+  double rgb_d[3] = {0.0, 0.0, 0.0};
+};
+
+ViewingConditions CreateViewingConditions(const double white_point[3],
+                                          const double adapting_luminance,
+                                          const double background_lstar,
+                                          const double surround,
+                                          const bool discounting_illuminant);
+
+ViewingConditions DefaultWithBackgroundLstar(const double background_lstar);
+
+static const ViewingConditions kDefaultViewingConditions = (ViewingConditions){
+    11.725676537,
+    50.000000000,
+    2.000000000,
+    false,
+    0.184186503,
+    29.981000900,
+    1.016919255,
+    1.016919255,
+    0.689999998,
+    1.000000000,
+    0.388481468,
+    0.789482653,
+    1.909169555,
+    {95.047, 100.0, 108.883},
+    {1.021177769, 0.986307740, 0.933960497},
+};
+
+}  // namespace material_color_utilities
+#endif  // CPP_CAM_VIEWING_CONDITIONS_H_

third_party/material_color_utilities/cpp/contrast/contrast.cc

@@ -0,0 +1,138 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "cpp/contrast/contrast.h"
+
+#include <algorithm>
+#include <cmath>
+
+#include "cpp/utils/utils.h"
+
+namespace material_color_utilities {
+// Given a color and a contrast ratio to reach, the luminance of a color that
+// reaches that ratio with the color can be calculated. However, that luminance
+// may not contrast as desired, i.e. the contrast ratio of the input color
+// and the returned luminance may not reach the contrast ratio  asked for.
+//
+// When the desired contrast ratio and the result contrast ratio differ by
+// more than this amount,  an error value should be returned, or the method
+// should be documented as 'unsafe', meaning, it will return a valid luminance
+// but that luminance may not meet the requested contrast ratio.
+//
+// 0.04 selected because it ensures the resulting ratio rounds to the
+// same tenth.
+constexpr double CONTRAST_RATIO_EPSILON = 0.04;
+
+// Color spaces that measure luminance, such as Y in XYZ, L* in L*a*b*,
+// or T in HCT, are known as  perceptual accurate color spaces.
+//
+// To be displayed, they must gamut map to a "display space", one that has
+// a defined limit on the number of colors. Display spaces include sRGB,
+// more commonly understood as RGB/HSL/HSV/HSB.
+//
+// Gamut mapping is undefined and not defined by the color space. Any
+// gamut mapping algorithm must choose how to sacrifice accuracy in hue,
+// saturation, and/or lightness.
+//
+// A principled solution is to maintain lightness, thus maintaining
+// contrast/a11y, maintain hue, thus maintaining aesthetic intent, and reduce
+// chroma until the color is in gamut.
+//
+// HCT chooses this solution, but, that doesn't mean it will _exactly_ matched
+// desired lightness, if only because RGB is quantized: RGB is expressed as
+// a set of integers: there may be an RGB color with, for example,
+// 47.892 lightness, but not 47.891.
+//
+// To allow for this inherent incompatibility between perceptually accurate
+// color spaces and display color spaces, methods that take a contrast ratio
+// and luminance, and return a luminance that reaches that contrast ratio for
+// the input luminance, purposefully darken/lighten their result such that
+// the desired contrast ratio will be reached even if inaccuracy is introduced.
+//
+// 0.4 is generous, ex. HCT requires much less delta. It was chosen because
+// it provides a rough guarantee that as long as a percetual color space
+// gamut maps lightness such that the resulting lightness rounds to the same
+// as the requested, the desired contrast ratio will be reached.
+constexpr double LUMINANCE_GAMUT_MAP_TOLERANCE = 0.4;
+
+double RatioOfYs(double y1, double y2) {
+  double lighter = y1 > y2 ? y1 : y2;
+  double darker = (lighter == y2) ? y1 : y2;
+  return (lighter + 5.0) / (darker + 5.0);
+}
+
+double RatioOfTones(double tone_a, double tone_b) {
+  tone_a = std::clamp(tone_a, 0.0, 100.0);
+  tone_b = std::clamp(tone_b, 0.0, 100.0);
+  return RatioOfYs(YFromLstar(tone_a), YFromLstar(tone_b));
+}
+
+double Lighter(double tone, double ratio) {
+  if (tone < 0.0 || tone > 100.0) {
+    return -1.0;
+  }
+
+  double dark_y = YFromLstar(tone);
+  double light_y = ratio * (dark_y + 5.0) - 5.0;
+  double real_contrast = RatioOfYs(light_y, dark_y);
+  double delta = abs(real_contrast - ratio);
+  if (real_contrast < ratio && delta > CONTRAST_RATIO_EPSILON) {
+    return -1;
+  }
+
+  // ensure gamut mapping, which requires a 'range' on tone, will still result
+  // the correct ratio by darkening slightly.
+  double value = LstarFromY(light_y) + LUMINANCE_GAMUT_MAP_TOLERANCE;
+  if (value < 0 || value > 100) {
+    return -1;
+  }
+  return value;
+}
+
+double Darker(double tone, double ratio) {
+  if (tone < 0.0 || tone > 100.0) {
+    return -1.0;
+  }
+
+  double light_y = YFromLstar(tone);
+  double dark_y = ((light_y + 5.0) / ratio) - 5.0;
+  double real_contrast = RatioOfYs(light_y, dark_y);
+
+  double delta = abs(real_contrast - ratio);
+  if (real_contrast < ratio && delta > CONTRAST_RATIO_EPSILON) {
+    return -1;
+  }
+
+  // ensure gamut mapping, which requires a 'range' on tone, will still result
+  // the correct ratio by darkening slightly.
+  double value = LstarFromY(dark_y) - LUMINANCE_GAMUT_MAP_TOLERANCE;
+  if (value < 0 || value > 100) {
+    return -1;
+  }
+  return value;
+}
+
+double LighterUnsafe(double tone, double ratio) {
+  double lighter_safe = Lighter(tone, ratio);
+  return (lighter_safe < 0.0) ? 100.0 : lighter_safe;
+}
+
+double DarkerUnsafe(double tone, double ratio) {
+  double darker_safe = Darker(tone, ratio);
+  return (darker_safe < 0.0) ? 0.0 : darker_safe;
+}
+
+}  // namespace material_color_utilities

third_party/material_color_utilities/cpp/contrast/contrast.h

@@ -0,0 +1,97 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CPP_CONTRAST_CONTRAST_H_
+#define CPP_CONTRAST_CONTRAST_H_
+
+/**
+ * Utility methods for calculating contrast given two colors, or calculating a
+ * color given one color and a contrast ratio.
+ *
+ * Contrast ratio is calculated using XYZ's Y. When linearized to match human
+ * perception, Y becomes HCT's tone and L*a*b*'s' L*. Informally, this is the
+ * lightness of a color.
+ *
+ * Methods refer to tone, T in the the HCT color space.
+ * Tone is equivalent to L* in the L*a*b* color space, or L in the LCH color
+ * space.
+ */
+namespace material_color_utilities {
+/**
+ * @return a contrast ratio, which ranges from 1 to 21.
+ * @param tone_a Tone between 0 and 100. Values outside will be clamped.
+ * @param tone_b Tone between 0 and 100. Values outside will be clamped.
+ */
+double RatioOfTones(double tone_a, double tone_b);
+
+/**
+ * @return a tone >= [tone] that ensures [ratio].
+ * Return value is between 0 and 100.
+ * Returns -1 if [ratio] cannot be achieved with [tone].
+ *
+ * @param tone Tone return value must contrast with.
+ * Range is 0 to 100. Invalid values will result in -1 being returned.
+ * @param ratio Contrast ratio of return value and [tone].
+ * Range is 1 to 21, invalid values have undefined behavior.
+ */
+double Lighter(double tone, double ratio);
+
+/**
+ * @return a tone <= [tone] that ensures [ratio].
+ * Return value is between 0 and 100.
+ * Returns -1 if [ratio] cannot be achieved with [tone].
+ *
+ * @param tone Tone return value must contrast with.
+ * Range is 0 to 100. Invalid values will result in -1 being returned.
+ * @param ratio Contrast ratio of return value and [tone].
+ * Range is 1 to 21, invalid values have undefined behavior.
+ */
+double Darker(double tone, double ratio);
+
+/**
+ * @return a tone >= [tone] that ensures [ratio].
+ * Return value is between 0 and 100.
+ * Returns 100 if [ratio] cannot be achieved with [tone].
+ *
+ * This method is unsafe because the returned value is guaranteed to be in
+ * bounds for tone, i.e. between 0 and 100. However, that value may not reach
+ * the [ratio] with [tone]. For example, there is no color lighter than T100.
+ *
+ * @param tone Tone return value must contrast with.
+ * Range is 0 to 100. Invalid values will result in 100 being returned.
+ * @param ratio Desired contrast ratio of return value and tone parameter.
+ * Range is 1 to 21, invalid values have undefined behavior.
+ */
+double LighterUnsafe(double tone, double ratio);
+
+/**
+ * @return a tone <= [tone] that ensures [ratio].
+ * Return value is between 0 and 100.
+ * Returns 0 if [ratio] cannot be achieved with [tone].
+ *
+ * This method is unsafe because the returned value is guaranteed to be in
+ * bounds for tone, i.e. between 0 and 100. However, that value may not reach
+ * the [ratio] with [tone]. For example, there is no color darker than T0.
+ *
+ * @param tone Tone return value must contrast with.
+ * Range is 0 to 100. Invalid values will result in 0 being returned.
+ * @param ratio Desired contrast ratio of return value and tone parameter.
+ * Range is 1 to 21, invalid values have undefined behavior.
+ */
+double DarkerUnsafe(double tone, double ratio);
+}  // namespace material_color_utilities
+
+#endif  // CPP_CONTRAST_CONTRAST_H_

third_party/material_color_utilities/cpp/dislike/dislike.cc

@@ -0,0 +1,42 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "cpp/dislike/dislike.h"
+
+#include <cmath>
+
+#include "cpp/cam/hct.h"
+
+namespace material_color_utilities {
+
+bool IsDisliked(Hct hct) {
+  double roundedHue = std::round(hct.get_hue());
+
+  bool hue_passes = roundedHue >= 90.0 && roundedHue <= 111.0;
+  bool chroma_passes = std::round(hct.get_chroma()) > 16.0;
+  bool tone_passes = std::round(hct.get_tone()) < 65.0;
+
+  return hue_passes && chroma_passes && tone_passes;
+}
+
+Hct FixIfDisliked(Hct hct) {
+  if (IsDisliked(hct)) {
+    return Hct(hct.get_hue(), hct.get_chroma(), 70.0);
+  }
+
+  return hct;
+}
+}  // namespace material_color_utilities

third_party/material_color_utilities/cpp/dislike/dislike.h

@@ -0,0 +1,55 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CPP_DISLIKE_DISLIKE_H_
+#define CPP_DISLIKE_DISLIKE_H_
+
+#include "cpp/cam/hct.h"
+
+namespace material_color_utilities {
+
+/**
+ * Checks and/or fixes universally disliked colors.
+ *
+ * Color science studies of color preference indicate universal distaste for
+ * dark yellow-greens, and also show this is correlated to distate for
+ * biological waste and rotting food.
+ *
+ * See Palmer and Schloss, 2010 or Schloss and Palmer's Chapter 21 in Handbook
+ * of Color Psychology (2015).
+ */
+
+/**
+ * @return whether the color is disliked.
+ *
+ * Disliked is defined as a dark yellow-green that is not neutral.
+ * @param hct The color to be tested.
+ */
+bool IsDisliked(Hct hct);
+
+/**
+ * If a color is disliked, lightens it to make it likable.
+ *
+ * The original color is not modified.
+ *
+ * @param hct The color to be tested (and fixed, if needed).
+ * @return The original color if it is not disliked; otherwise, the fixed
+ *     color.
+ */
+Hct FixIfDisliked(Hct hct);
+}  // namespace material_color_utilities
+
+#endif  // CPP_DISLIKE_DISLIKE_H_

third_party/material_color_utilities/cpp/dynamiccolor/contrast_curve.h

@@ -0,0 +1,72 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CPP_DYNAMICCOLOR_CONTRAST_CURVE_H_
+#define CPP_DYNAMICCOLOR_CONTRAST_CURVE_H_
+
+#include "cpp/utils/utils.h"
+
+namespace material_color_utilities {
+
+/**
+ * A class containing a value that changes with the contrast level.
+ *
+ * Usually represents the contrast requirements for a dynamic color on its
+ * background. The four values correspond to values for contrast levels -1.0,
+ * 0.0, 0.5, and 1.0, respectively.
+ */
+struct ContrastCurve {
+  double low;
+  double normal;
+  double medium;
+  double high;
+
+  /**
+   * Creates a `ContrastCurve` object.
+   *
+   * @param low Value for contrast level -1.0
+   * @param normal Value for contrast level 0.0
+   * @param medium Value for contrast level 0.5
+   * @param high Value for contrast level 1.0
+   */
+  ContrastCurve(double low, double normal, double medium, double high)
+      : low(low), normal(normal), medium(medium), high(high) {}
+
+  /**
+   * Returns the value at a given contrast level.
+   *
+   * @param contrastLevel The contrast level. 0.0 is the default (normal); -1.0
+   *     is the lowest; 1.0 is the highest.
+   * @return The value. For contrast ratios, a number between 1.0 and 21.0.
+   */
+  double get(double contrastLevel) {
+    if (contrastLevel <= -1.0) {
+      return low;
+    } else if (contrastLevel < 0.0) {
+      return Lerp(low, normal, (contrastLevel - (-1)) / 1);
+    } else if (contrastLevel < 0.5) {
+      return Lerp(normal, medium, (contrastLevel - 0) / 0.5);
+    } else if (contrastLevel < 1.0) {
+      return Lerp(medium, high, (contrastLevel - 0.5) / 0.5);
+    } else {
+      return high;
+    }
+  }
+};
+
+}  // namespace material_color_utilities
+
+#endif  // CPP_DYNAMICCOLOR_CONTRAST_CURVE_H_

third_party/material_color_utilities/cpp/dynamiccolor/dynamic_color.cc

@@ -0,0 +1,306 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "cpp/dynamiccolor/dynamic_color.h"
+
+#include <algorithm>
+#include <cmath>
+#include <functional>
+#include <optional>
+#include <string>
+#include <vector>
+
+#include "cpp/cam/hct.h"
+#include "cpp/contrast/contrast.h"
+#include "cpp/dynamiccolor/dynamic_scheme.h"
+#include "cpp/dynamiccolor/tone_delta_pair.h"
+#include "cpp/palettes/tones.h"
+
+namespace material_color_utilities {
+
+using std::function;
+using std::nullopt;
+using std::optional;
+
+using DoubleFunction = function<double(const DynamicScheme&)>;
+
+template <class T, class U>
+optional<U> SafeCall(optional<function<optional<U>(const T&)>> f, const T& x) {
+  if (f == nullopt) {
+    return nullopt;
+  } else {
+    return f.value()(x);
+  }
+}
+
+template <class T, class U>
+optional<U> SafeCallCleanResult(optional<function<U(T)>> f, T x) {
+  if (f == nullopt) {
+    return nullopt;
+  } else {
+    return f.value()(x);
+  }
+}
+
+double ForegroundTone(double bg_tone, double ratio) {
+  double lighter_tone = LighterUnsafe(/*tone*/ bg_tone, /*ratio*/ ratio);
+  double darker_tone = DarkerUnsafe(/*tone*/ bg_tone, /*ratio*/ ratio);
+  double lighter_ratio = RatioOfTones(lighter_tone, bg_tone);
+  double darker_ratio = RatioOfTones(darker_tone, bg_tone);
+  double prefer_lighter = TonePrefersLightForeground(bg_tone);
+
+  if (prefer_lighter) {
+    double negligible_difference =
+        (abs(lighter_ratio - darker_ratio) < 0.1 && lighter_ratio < ratio &&
+         darker_ratio < ratio);
+    return lighter_ratio >= ratio || lighter_ratio >= darker_ratio ||
+                   negligible_difference
+               ? lighter_tone
+               : darker_tone;
+  } else {
+    return darker_ratio >= ratio || darker_ratio >= lighter_ratio
+               ? darker_tone
+               : lighter_tone;
+  }
+}
+
+double EnableLightForeground(double tone) {
+  if (TonePrefersLightForeground(tone) && !ToneAllowsLightForeground(tone)) {
+    return 49.0;
+  }
+  return tone;
+}
+
+bool TonePrefersLightForeground(double tone) { return round(tone) < 60; }
+
+bool ToneAllowsLightForeground(double tone) { return round(tone) <= 49; }
+
+/**
+ * Default constructor.
+ */
+DynamicColor::DynamicColor(
+    std::string name, std::function<TonalPalette(const DynamicScheme&)> palette,
+    std::function<double(const DynamicScheme&)> tone, bool is_background,
+
+    std::optional<std::function<DynamicColor(const DynamicScheme&)>> background,
+    std::optional<std::function<DynamicColor(const DynamicScheme&)>>
+        second_background,
+    std::optional<ContrastCurve> contrast_curve,
+    std::optional<std::function<ToneDeltaPair(const DynamicScheme&)>>
+        tone_delta_pair)
+    : name_(name),
+      palette_(palette),
+      tone_(tone),
+      is_background_(is_background),
+      background_(background),
+      second_background_(second_background),
+      contrast_curve_(contrast_curve),
+      tone_delta_pair_(tone_delta_pair) {}
+
+DynamicColor DynamicColor::FromPalette(
+    std::string name, std::function<TonalPalette(const DynamicScheme&)> palette,
+    std::function<double(const DynamicScheme&)> tone) {
+  return DynamicColor(name, palette, tone,
+                      /*is_background=*/false,
+                      /*background=*/nullopt,
+                      /*second_background=*/nullopt,
+                      /*contrast_curve=*/nullopt,
+                      /*tone_delta_pair=*/nullopt);
+}
+
+Argb DynamicColor::GetArgb(const DynamicScheme& scheme) {
+  return palette_(scheme).get(GetTone(scheme));
+}
+
+Hct DynamicColor::GetHct(const DynamicScheme& scheme) {
+  return Hct(GetArgb(scheme));
+}
+
+double DynamicColor::GetTone(const DynamicScheme& scheme) {
+  bool decreasingContrast = scheme.contrast_level < 0;
+
+  // Case 1: dual foreground, pair of colors with delta constraint.
+  if (tone_delta_pair_ != std::nullopt) {
+    ToneDeltaPair tone_delta_pair = tone_delta_pair_.value()(scheme);
+    DynamicColor role_a = tone_delta_pair.role_a_;
+    DynamicColor role_b = tone_delta_pair.role_b_;
+    double delta = tone_delta_pair.delta_;
+    TonePolarity polarity = tone_delta_pair.polarity_;
+    bool stay_together = tone_delta_pair.stay_together_;
+
+    DynamicColor bg = background_.value()(scheme);
+    double bg_tone = bg.GetTone(scheme);
+
+    bool a_is_nearer =
+        (polarity == TonePolarity::kNearer ||
+         (polarity == TonePolarity::kLighter && !scheme.is_dark) ||
+         (polarity == TonePolarity::kDarker && scheme.is_dark));
+    DynamicColor nearer = a_is_nearer ? role_a : role_b;
+    DynamicColor farther = a_is_nearer ? role_b : role_a;
+    bool am_nearer = this->name_ == nearer.name_;
+    double expansion_dir = scheme.is_dark ? 1 : -1;
+
+    // 1st round: solve to min, each
+    double n_contrast =
+        nearer.contrast_curve_.value().get(scheme.contrast_level);
+    double f_contrast =
+        farther.contrast_curve_.value().get(scheme.contrast_level);
+
+    // If a color is good enough, it is not adjusted.
+    // Initial and adjusted tones for `nearer`
+    double n_initial_tone = nearer.tone_(scheme);
+    double n_tone = RatioOfTones(bg_tone, n_initial_tone) >= n_contrast
+                        ? n_initial_tone
+                        : ForegroundTone(bg_tone, n_contrast);
+    // Initial and adjusted tones for `farther`
+    double f_initial_tone = farther.tone_(scheme);
+    double f_tone = RatioOfTones(bg_tone, f_initial_tone) >= f_contrast
+                        ? f_initial_tone
+                        : ForegroundTone(bg_tone, f_contrast);
+
+    if (decreasingContrast) {
+      // If decreasing contrast, adjust color to the "bare minimum"
+      // that satisfies contrast.
+      n_tone = ForegroundTone(bg_tone, n_contrast);
+      f_tone = ForegroundTone(bg_tone, f_contrast);
+    }
+
+    if ((f_tone - n_tone) * expansion_dir >= delta) {
+      // Good! Tones satisfy the constraint; no change needed.
+    } else {
+      // 2nd round: expand farther to match delta.
+      f_tone = std::clamp(n_tone + delta * expansion_dir, 0.0, 100.0);
+      if ((f_tone - n_tone) * expansion_dir >= delta) {
+        // Good! Tones now satisfy the constraint; no change needed.
+      } else {
+        // 3rd round: contract nearer to match delta.
+        n_tone = std::clamp(f_tone - delta * expansion_dir, 0.0, 100.0);
+      }
+    }
+
+    // Avoids the 50-59 awkward zone.
+    if (50 <= n_tone && n_tone < 60) {
+      // If `nearer` is in the awkward zone, move it away, together with
+      // `farther`.
+      if (expansion_dir > 0) {
+        n_tone = 60;
+        f_tone = std::max(f_tone, n_tone + delta * expansion_dir);
+      } else {
+        n_tone = 49;
+        f_tone = std::min(f_tone, n_tone + delta * expansion_dir);
+      }
+    } else if (50 <= f_tone && f_tone < 60) {
+      if (stay_together) {
+        // Fixes both, to avoid two colors on opposite sides of the "awkward
+        // zone".
+        if (expansion_dir > 0) {
+          n_tone = 60;
+          f_tone = std::max(f_tone, n_tone + delta * expansion_dir);
+        } else {
+          n_tone = 49;
+          f_tone = std::min(f_tone, n_tone + delta * expansion_dir);
+        }
+      } else {
+        // Not required to stay together; fixes just one.
+        if (expansion_dir > 0) {
+          f_tone = 60;
+        } else {
+          f_tone = 49;
+        }
+      }
+    }
+
+    // Returns `n_tone` if this color is `nearer`, otherwise `f_tone`.
+    return am_nearer ? n_tone : f_tone;
+  } else {
+    // Case 2: No contrast pair; just solve for itself.
+    double answer = tone_(scheme);
+
+    if (background_ == std::nullopt) {
+      return answer;  // No adjustment for colors with no background.
+    }
+
+    double bg_tone = background_.value()(scheme).GetTone(scheme);
+
+    double desired_ratio = contrast_curve_.value().get(scheme.contrast_level);
+
+    if (RatioOfTones(bg_tone, answer) >= desired_ratio) {
+      // Don't "improve" what's good enough.
+    } else {
+      // Rough improvement.
+      answer = ForegroundTone(bg_tone, desired_ratio);
+    }
+
+    if (decreasingContrast) {
+      answer = ForegroundTone(bg_tone, desired_ratio);
+    }
+
+    if (is_background_ && 50 <= answer && answer < 60) {
+      // Must adjust
+      if (RatioOfTones(49, bg_tone) >= desired_ratio) {
+        answer = 49;
+      } else {
+        answer = 60;
+      }
+    }
+
+    if (second_background_ != std::nullopt) {
+      // Case 3: Adjust for dual backgrounds.
+
+      double bg_tone_1 = background_.value()(scheme).GetTone(scheme);
+      double bg_tone_2 = second_background_.value()(scheme).GetTone(scheme);
+
+      double upper = std::max(bg_tone_1, bg_tone_2);
+      double lower = std::min(bg_tone_1, bg_tone_2);
+
+      if (RatioOfTones(upper, answer) >= desired_ratio &&
+          RatioOfTones(lower, answer) >= desired_ratio) {
+        return answer;
+      }
+
+      // The darkest light tone that satisfies the desired ratio,
+      // or -1 if such ratio cannot be reached.
+      double lightOption = Lighter(upper, desired_ratio);
+
+      // The lightest dark tone that satisfies the desired ratio,
+      // or -1 if such ratio cannot be reached.
+      double darkOption = Darker(lower, desired_ratio);
+
+      // Tones suitable for the foreground.
+      std::vector<double> availables;
+      if (lightOption != -1) {
+        availables.push_back(lightOption);
+      }
+      if (darkOption != -1) {
+        availables.push_back(darkOption);
+      }
+
+      bool prefersLight = TonePrefersLightForeground(bg_tone_1) ||
+                          TonePrefersLightForeground(bg_tone_2);
+      if (prefersLight) {
+        return (lightOption < 0) ? 100 : lightOption;
+      }
+      if (availables.size() == 1) {
+        return availables[0];
+      }
+      return (darkOption < 0) ? 0 : darkOption;
+    }
+
+    return answer;
+  }
+}
+
+}  // namespace material_color_utilities

third_party/material_color_utilities/cpp/dynamiccolor/dynamic_color.h

@@ -0,0 +1,131 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CPP_DYNAMICCOLOR_DYNAMIC_COLOR_H_
+#define CPP_DYNAMICCOLOR_DYNAMIC_COLOR_H_
+
+#include <functional>
+#include <optional>
+#include <string>
+
+#include "cpp/cam/hct.h"
+#include "cpp/dynamiccolor/contrast_curve.h"
+#include "cpp/dynamiccolor/dynamic_scheme.h"
+#include "cpp/utils/utils.h"
+
+namespace material_color_utilities {
+
+struct ToneDeltaPair;
+
+/**
+ * Given a background tone, find a foreground tone, while ensuring they reach
+ * a contrast ratio that is as close to [ratio] as possible.
+ *
+ * [bgTone] Tone in HCT. Range is 0 to 100, undefined behavior when it falls
+ * outside that range.
+ * [ratio] The contrast ratio desired between [bgTone] and the return value.
+ */
+double ForegroundTone(double bg_tone, double ratio);
+
+/**
+ * Adjust a tone such that white has 4.5 contrast, if the tone is
+ * reasonably close to supporting it.
+ */
+double EnableLightForeground(double tone);
+
+/**
+ * Returns whether [tone] prefers a light foreground.
+ *
+ * People prefer white foregrounds on ~T60-70. Observed over time, and also
+ * by Andrew Somers during research for APCA.
+ *
+ * T60 used as to create the smallest discontinuity possible when skipping
+ * down to T49 in order to ensure light foregrounds.
+ *
+ * Since `tertiaryContainer` in dark monochrome scheme requires a tone of
+ * 60, it should not be adjusted. Therefore, 60 is excluded here.
+ */
+bool TonePrefersLightForeground(double tone);
+
+/**
+ * Returns whether [tone] can reach a contrast ratio of 4.5 with a lighter
+ * color.
+ */
+bool ToneAllowsLightForeground(double tone);
+
+/**
+ * @param name_ The name of the dynamic color.
+ * @param palette_ Function that provides a TonalPalette given
+ * DynamicScheme. A TonalPalette is defined by a hue and chroma, so this
+ * replaces the need to specify hue/chroma. By providing a tonal palette, when
+ * contrast adjustments are made, intended chroma can be preserved.
+ * @param tone_ Function that provides a tone given DynamicScheme.
+ * @param is_background_ Whether this dynamic color is a background, with
+ * some other color as the foreground.
+ * @param background_ The background of the dynamic color (as a function of a
+ *     `DynamicScheme`), if it exists.
+ * @param second_background_ A second background of the dynamic color (as a
+ *     function of a `DynamicScheme`), if it
+ * exists.
+ * @param contrast_curve_ A `ContrastCurve` object specifying how its contrast
+ * against its background should behave in various contrast levels options.
+ * @param tone_delta_pair_ A `ToneDeltaPair` object specifying a tone delta
+ * constraint between two colors. One of them must be the color being
+ * constructed.
+ */
+struct DynamicColor {
+  std::string name_;
+  std::function<TonalPalette(const DynamicScheme&)> palette_;
+  std::function<double(const DynamicScheme&)> tone_;
+  bool is_background_;
+
+  std::optional<std::function<DynamicColor(const DynamicScheme&)>> background_;
+  std::optional<std::function<DynamicColor(const DynamicScheme&)>>
+      second_background_;
+  std::optional<ContrastCurve> contrast_curve_;
+  std::optional<std::function<ToneDeltaPair(const DynamicScheme&)>>
+      tone_delta_pair_;
+
+  /** A convenience constructor, only requiring name, palette, and tone. */
+  static DynamicColor FromPalette(
+      std::string name,
+      std::function<TonalPalette(const DynamicScheme&)> palette,
+      std::function<double(const DynamicScheme&)> tone);
+
+  Argb GetArgb(const DynamicScheme& scheme);
+
+  Hct GetHct(const DynamicScheme& scheme);
+
+  double GetTone(const DynamicScheme& scheme);
+
+  /** The default constructor. */
+  DynamicColor(std::string name,
+               std::function<TonalPalette(const DynamicScheme&)> palette,
+               std::function<double(const DynamicScheme&)> tone,
+               bool is_background,
+
+               std::optional<std::function<DynamicColor(const DynamicScheme&)>>
+                   background,
+               std::optional<std::function<DynamicColor(const DynamicScheme&)>>
+                   second_background,
+               std::optional<ContrastCurve> contrast_curve,
+               std::optional<std::function<ToneDeltaPair(const DynamicScheme&)>>
+                   tone_delta_pair);
+};
+
+}  // namespace material_color_utilities
+
+#endif  // CPP_DYNAMICCOLOR_DYNAMIC_COLOR_H_

third_party/material_color_utilities/cpp/dynamiccolor/dynamic_scheme.cc

@@ -0,0 +1,286 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "cpp/dynamiccolor/dynamic_scheme.h"
+
+#include <optional>
+#include <vector>
+
+#include "cpp/cam/hct.h"
+#include "cpp/dynamiccolor/material_dynamic_colors.h"
+#include "cpp/dynamiccolor/variant.h"
+#include "cpp/palettes/tones.h"
+#include "cpp/utils/utils.h"
+
+namespace material_color_utilities {
+
+DynamicScheme::DynamicScheme(Hct source_color_hct, Variant variant,
+                             double contrast_level, bool is_dark,
+                             TonalPalette primary_palette,
+                             TonalPalette secondary_palette,
+                             TonalPalette tertiary_palette,
+                             TonalPalette neutral_palette,
+                             TonalPalette neutral_variant_palette,
+                             std::optional<TonalPalette> error_palette)
+    : source_color_hct(source_color_hct),
+      variant(variant),
+      is_dark(is_dark),
+      contrast_level(contrast_level),
+      primary_palette(primary_palette),
+      secondary_palette(secondary_palette),
+      tertiary_palette(tertiary_palette),
+      neutral_palette(neutral_palette),
+      neutral_variant_palette(neutral_variant_palette),
+      error_palette(error_palette.value_or(TonalPalette(25.0, 84.0))) {}
+
+double DynamicScheme::GetRotatedHue(Hct source_color, std::vector<double> hues,
+                                    std::vector<double> rotations) {
+  double source_hue = source_color.get_hue();
+
+  if (rotations.size() == 1) {
+    return SanitizeDegreesDouble(source_color.get_hue() + rotations[0]);
+  }
+  int size = hues.size();
+  for (int i = 0; i <= (size - 2); ++i) {
+    double this_hue = hues[i];
+    double next_hue = hues[i + 1];
+    if (this_hue < source_hue && source_hue < next_hue) {
+      return SanitizeDegreesDouble(source_hue + rotations[i]);
+    }
+  }
+
+  return source_hue;
+}
+
+Argb DynamicScheme::SourceColorArgb() const { return source_color_hct.ToInt(); }
+
+Argb DynamicScheme::GetPrimaryPaletteKeyColor() const {
+  return MaterialDynamicColors::PrimaryPaletteKeyColor().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetSecondaryPaletteKeyColor() const {
+  return MaterialDynamicColors::SecondaryPaletteKeyColor().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetTertiaryPaletteKeyColor() const {
+  return MaterialDynamicColors::TertiaryPaletteKeyColor().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetNeutralPaletteKeyColor() const {
+  return MaterialDynamicColors::NeutralPaletteKeyColor().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetNeutralVariantPaletteKeyColor() const {
+  return MaterialDynamicColors::NeutralVariantPaletteKeyColor().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetBackground() const {
+  return MaterialDynamicColors::Background().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetOnBackground() const {
+  return MaterialDynamicColors::OnBackground().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetSurface() const {
+  return MaterialDynamicColors::Surface().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetSurfaceDim() const {
+  return MaterialDynamicColors::SurfaceDim().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetSurfaceBright() const {
+  return MaterialDynamicColors::SurfaceBright().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetSurfaceContainerLowest() const {
+  return MaterialDynamicColors::SurfaceContainerLowest().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetSurfaceContainerLow() const {
+  return MaterialDynamicColors::SurfaceContainerLow().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetSurfaceContainer() const {
+  return MaterialDynamicColors::SurfaceContainer().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetSurfaceContainerHigh() const {
+  return MaterialDynamicColors::SurfaceContainerHigh().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetSurfaceContainerHighest() const {
+  return MaterialDynamicColors::SurfaceContainerHighest().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetOnSurface() const {
+  return MaterialDynamicColors::OnSurface().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetSurfaceVariant() const {
+  return MaterialDynamicColors::SurfaceVariant().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetOnSurfaceVariant() const {
+  return MaterialDynamicColors::OnSurfaceVariant().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetInverseSurface() const {
+  return MaterialDynamicColors::InverseSurface().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetInverseOnSurface() const {
+  return MaterialDynamicColors::InverseOnSurface().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetOutline() const {
+  return MaterialDynamicColors::Outline().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetOutlineVariant() const {
+  return MaterialDynamicColors::OutlineVariant().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetShadow() const {
+  return MaterialDynamicColors::Shadow().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetScrim() const {
+  return MaterialDynamicColors::Scrim().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetSurfaceTint() const {
+  return MaterialDynamicColors::SurfaceTint().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetPrimary() const {
+  return MaterialDynamicColors::Primary().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetOnPrimary() const {
+  return MaterialDynamicColors::OnPrimary().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetPrimaryContainer() const {
+  return MaterialDynamicColors::PrimaryContainer().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetOnPrimaryContainer() const {
+  return MaterialDynamicColors::OnPrimaryContainer().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetInversePrimary() const {
+  return MaterialDynamicColors::InversePrimary().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetSecondary() const {
+  return MaterialDynamicColors::Secondary().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetOnSecondary() const {
+  return MaterialDynamicColors::OnSecondary().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetSecondaryContainer() const {
+  return MaterialDynamicColors::SecondaryContainer().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetOnSecondaryContainer() const {
+  return MaterialDynamicColors::OnSecondaryContainer().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetTertiary() const {
+  return MaterialDynamicColors::Tertiary().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetOnTertiary() const {
+  return MaterialDynamicColors::OnTertiary().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetTertiaryContainer() const {
+  return MaterialDynamicColors::TertiaryContainer().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetOnTertiaryContainer() const {
+  return MaterialDynamicColors::OnTertiaryContainer().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetError() const {
+  return MaterialDynamicColors::Error().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetOnError() const {
+  return MaterialDynamicColors::OnError().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetErrorContainer() const {
+  return MaterialDynamicColors::ErrorContainer().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetOnErrorContainer() const {
+  return MaterialDynamicColors::OnErrorContainer().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetPrimaryFixed() const {
+  return MaterialDynamicColors::PrimaryFixed().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetPrimaryFixedDim() const {
+  return MaterialDynamicColors::PrimaryFixedDim().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetOnPrimaryFixed() const {
+  return MaterialDynamicColors::OnPrimaryFixed().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetOnPrimaryFixedVariant() const {
+  return MaterialDynamicColors::OnPrimaryFixedVariant().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetSecondaryFixed() const {
+  return MaterialDynamicColors::SecondaryFixed().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetSecondaryFixedDim() const {
+  return MaterialDynamicColors::SecondaryFixedDim().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetOnSecondaryFixed() const {
+  return MaterialDynamicColors::OnSecondaryFixed().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetOnSecondaryFixedVariant() const {
+  return MaterialDynamicColors::OnSecondaryFixedVariant().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetTertiaryFixed() const {
+  return MaterialDynamicColors::TertiaryFixed().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetTertiaryFixedDim() const {
+  return MaterialDynamicColors::TertiaryFixedDim().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetOnTertiaryFixed() const {
+  return MaterialDynamicColors::OnTertiaryFixed().GetArgb(*this);
+}
+
+Argb DynamicScheme::GetOnTertiaryFixedVariant() const {
+  return MaterialDynamicColors::OnTertiaryFixedVariant().GetArgb(*this);
+}
+
+}  // namespace material_color_utilities

third_party/material_color_utilities/cpp/dynamiccolor/dynamic_scheme.h

@@ -0,0 +1,113 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CPP_DYNAMICCOLOR_DYNAMIC_SCHEME_H_
+#define CPP_DYNAMICCOLOR_DYNAMIC_SCHEME_H_
+
+#include <optional>
+#include <vector>
+
+#include "cpp/cam/hct.h"
+#include "cpp/dynamiccolor/variant.h"
+#include "cpp/palettes/tones.h"
+#include "cpp/utils/utils.h"
+
+namespace material_color_utilities {
+
+struct DynamicScheme {
+  Hct source_color_hct;
+  Variant variant;
+  bool is_dark;
+  double contrast_level;
+
+  TonalPalette primary_palette;
+  TonalPalette secondary_palette;
+  TonalPalette tertiary_palette;
+  TonalPalette neutral_palette;
+  TonalPalette neutral_variant_palette;
+  TonalPalette error_palette;
+
+  DynamicScheme(Hct source_color_hct, Variant variant, double contrast_level,
+                bool is_dark, TonalPalette primary_palette,
+                TonalPalette secondary_palette, TonalPalette tertiary_palette,
+                TonalPalette neutral_palette,
+                TonalPalette neutral_variant_palette,
+                std::optional<TonalPalette> error_palette = std::nullopt);
+
+  static double GetRotatedHue(Hct source_color, std::vector<double> hues,
+                              std::vector<double> rotations);
+
+  Argb SourceColorArgb() const;
+
+  Argb GetPrimaryPaletteKeyColor() const;
+  Argb GetSecondaryPaletteKeyColor() const;
+  Argb GetTertiaryPaletteKeyColor() const;
+  Argb GetNeutralPaletteKeyColor() const;
+  Argb GetNeutralVariantPaletteKeyColor() const;
+  Argb GetBackground() const;
+  Argb GetOnBackground() const;
+  Argb GetSurface() const;
+  Argb GetSurfaceDim() const;
+  Argb GetSurfaceBright() const;
+  Argb GetSurfaceContainerLowest() const;
+  Argb GetSurfaceContainerLow() const;
+  Argb GetSurfaceContainer() const;
+  Argb GetSurfaceContainerHigh() const;
+  Argb GetSurfaceContainerHighest() const;
+  Argb GetOnSurface() const;
+  Argb GetSurfaceVariant() const;
+  Argb GetOnSurfaceVariant() const;
+  Argb GetInverseSurface() const;
+  Argb GetInverseOnSurface() const;
+  Argb GetOutline() const;
+  Argb GetOutlineVariant() const;
+  Argb GetShadow() const;
+  Argb GetScrim() const;
+  Argb GetSurfaceTint() const;
+  Argb GetPrimary() const;
+  Argb GetOnPrimary() const;
+  Argb GetPrimaryContainer() const;
+  Argb GetOnPrimaryContainer() const;
+  Argb GetInversePrimary() const;
+  Argb GetSecondary() const;
+  Argb GetOnSecondary() const;
+  Argb GetSecondaryContainer() const;
+  Argb GetOnSecondaryContainer() const;
+  Argb GetTertiary() const;
+  Argb GetOnTertiary() const;
+  Argb GetTertiaryContainer() const;
+  Argb GetOnTertiaryContainer() const;
+  Argb GetError() const;
+  Argb GetOnError() const;
+  Argb GetErrorContainer() const;
+  Argb GetOnErrorContainer() const;
+  Argb GetPrimaryFixed() const;
+  Argb GetPrimaryFixedDim() const;
+  Argb GetOnPrimaryFixed() const;
+  Argb GetOnPrimaryFixedVariant() const;
+  Argb GetSecondaryFixed() const;
+  Argb GetSecondaryFixedDim() const;
+  Argb GetOnSecondaryFixed() const;
+  Argb GetOnSecondaryFixedVariant() const;
+  Argb GetTertiaryFixed() const;
+  Argb GetTertiaryFixedDim() const;
+  Argb GetOnTertiaryFixed() const;
+  Argb GetOnTertiaryFixedVariant() const;
+};
+
+}  // namespace material_color_utilities
+
+#endif  // CPP_DYNAMICCOLOR_DYNAMIC_SCHEME_H_

third_party/material_color_utilities/cpp/dynamiccolor/material_dynamic_colors.h

@@ -0,0 +1,84 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CPP_DYNAMICCOLOR_MATERIAL_DYNAMIC_COLORS_H_
+#define CPP_DYNAMICCOLOR_MATERIAL_DYNAMIC_COLORS_H_
+
+#include "cpp/dynamiccolor/dynamic_color.h"
+
+namespace material_color_utilities {
+
+class MaterialDynamicColors {
+ public:
+  static DynamicColor PrimaryPaletteKeyColor();
+  static DynamicColor SecondaryPaletteKeyColor();
+  static DynamicColor TertiaryPaletteKeyColor();
+  static DynamicColor NeutralPaletteKeyColor();
+  static DynamicColor NeutralVariantPaletteKeyColor();
+  static DynamicColor Background();
+  static DynamicColor OnBackground();
+  static DynamicColor Surface();
+  static DynamicColor SurfaceDim();
+  static DynamicColor SurfaceBright();
+  static DynamicColor SurfaceContainerLowest();
+  static DynamicColor SurfaceContainerLow();
+  static DynamicColor SurfaceContainer();
+  static DynamicColor SurfaceContainerHigh();
+  static DynamicColor SurfaceContainerHighest();
+  static DynamicColor OnSurface();
+  static DynamicColor SurfaceVariant();
+  static DynamicColor OnSurfaceVariant();
+  static DynamicColor InverseSurface();
+  static DynamicColor InverseOnSurface();
+  static DynamicColor Outline();
+  static DynamicColor OutlineVariant();
+  static DynamicColor Shadow();
+  static DynamicColor Scrim();
+  static DynamicColor SurfaceTint();
+  static DynamicColor Primary();
+  static DynamicColor OnPrimary();
+  static DynamicColor PrimaryContainer();
+  static DynamicColor OnPrimaryContainer();
+  static DynamicColor InversePrimary();
+  static DynamicColor Secondary();
+  static DynamicColor OnSecondary();
+  static DynamicColor SecondaryContainer();
+  static DynamicColor OnSecondaryContainer();
+  static DynamicColor Tertiary();
+  static DynamicColor OnTertiary();
+  static DynamicColor TertiaryContainer();
+  static DynamicColor OnTertiaryContainer();
+  static DynamicColor Error();
+  static DynamicColor OnError();
+  static DynamicColor ErrorContainer();
+  static DynamicColor OnErrorContainer();
+  static DynamicColor PrimaryFixed();
+  static DynamicColor PrimaryFixedDim();
+  static DynamicColor OnPrimaryFixed();
+  static DynamicColor OnPrimaryFixedVariant();
+  static DynamicColor SecondaryFixed();
+  static DynamicColor SecondaryFixedDim();
+  static DynamicColor OnSecondaryFixed();
+  static DynamicColor OnSecondaryFixedVariant();
+  static DynamicColor TertiaryFixed();
+  static DynamicColor TertiaryFixedDim();
+  static DynamicColor OnTertiaryFixed();
+  static DynamicColor OnTertiaryFixedVariant();
+};
+
+}  // namespace material_color_utilities
+
+#endif  // CPP_DYNAMICCOLOR_MATERIAL_DYNAMIC_COLORS_H_

third_party/material_color_utilities/cpp/dynamiccolor/tone_delta_pair.h

@@ -0,0 +1,78 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CPP_DYNAMICCOLOR_TONE_DELTA_PAIR_H_
+#define CPP_DYNAMICCOLOR_TONE_DELTA_PAIR_H_
+
+#include "cpp/dynamiccolor/dynamic_color.h"
+
+namespace material_color_utilities {
+
+/**
+ * Describes the different in tone between colors.
+ */
+enum class TonePolarity { kDarker, kLighter, kNearer, kFarther };
+
+/**
+ * Documents a constraint between two DynamicColors, in which their tones must
+ * have a certain distance from each other.
+ *
+ * Prefer a DynamicColor with a background, this is for special cases when
+ * designers want tonal distance, literally contrast, between two colors that
+ * don't have a background / foreground relationship or a contrast guarantee.
+ */
+struct ToneDeltaPair {
+  DynamicColor role_a_;
+  DynamicColor role_b_;
+  double delta_;
+  TonePolarity polarity_;
+  bool stay_together_;
+
+  /**
+   * Documents a constraint in tone distance between two DynamicColors.
+   *
+   * The polarity is an adjective that describes "A", compared to "B".
+   *
+   * For instance, ToneDeltaPair(A, B, 15, 'darker', stayTogether) states that
+   * A's tone should be at least 15 darker than B's.
+   *
+   * 'nearer' and 'farther' describes closeness to the surface roles. For
+   * instance, ToneDeltaPair(A, B, 10, 'nearer', stayTogether) states that A
+   * should be 10 lighter than B in light mode, and 10 darker than B in dark
+   * mode.
+   *
+   * @param roleA The first role in a pair.
+   * @param roleB The second role in a pair.
+   * @param delta Required difference between tones. Absolute value, negative
+   * values have undefined behavior.
+   * @param polarity The relative relation between tones of roleA and roleB,
+   * as described above.
+   * @param stayTogether Whether these two roles should stay on the same side of
+   * the "awkward zone" (T50-59). This is necessary for certain cases where
+   * one role has two backgrounds.
+   */
+  ToneDeltaPair(DynamicColor role_a, DynamicColor role_b, double delta,
+                TonePolarity polarity, bool stay_together)
+      : role_a_(role_a),
+        role_b_(role_b),
+        delta_(delta),
+        polarity_(polarity),
+        stay_together_(stay_together) {}
+};
+
+}  // namespace material_color_utilities
+
+#endif  // CPP_DYNAMICCOLOR_TONE_DELTA_PAIR_H_

third_party/material_color_utilities/cpp/dynamiccolor/variant.h

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CPP_DYNAMICCOLOR_VARIANT_H_
+#define CPP_DYNAMICCOLOR_VARIANT_H_
+
+namespace material_color_utilities {
+
+enum class Variant {
+  kMonochrome,
+  kNeutral,
+  kTonalSpot,
+  kVibrant,
+  kExpressive,
+  kFidelity,
+  kContent,
+  kRainbow,
+  kFruitSalad,
+};
+
+}  // namespace material_color_utilities
+
+#endif  // CPP_DYNAMICCOLOR_VARIANT_H_

third_party/material_color_utilities/cpp/palettes/core.h

@@ -0,0 +1,39 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CPP_PALETTES_CORE_H_
+#define CPP_PALETTES_CORE_H_
+
+#include "cpp/palettes/tones.h"
+
+namespace material_color_utilities {
+
+/**
+ * Comprises foundational palettes to build a color scheme. Generated from a
+ * source color, these palettes will then be part of a [DynamicScheme] together
+ * with appearance preferences.
+*/
+typedef struct {
+    TonalPalette primary;
+    TonalPalette secondary;
+    TonalPalette tertiary;
+    TonalPalette neutral;
+    TonalPalette neutral_variant;
+} CorePalettes;
+
+}  // namespace material_color_utilities
+
+#endif  // CPP_PALETTES_CORE_H_

third_party/material_color_utilities/cpp/palettes/tones.cc

@@ -0,0 +1,116 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "cpp/palettes/tones.h"
+
+#include <cmath>
+
+#include "cpp/cam/cam.h"
+#include "cpp/cam/hct.h"
+
+namespace material_color_utilities {
+
+TonalPalette::TonalPalette(Argb argb) : key_color_(0.0, 0.0, 0.0) {
+  Cam cam = CamFromInt(argb);
+  hue_ = cam.hue;
+  chroma_ = cam.chroma;
+  key_color_ = KeyColor(cam.hue, cam.chroma).create();
+}
+
+TonalPalette::TonalPalette(Hct hct)
+    : key_color_(hct.get_hue(), hct.get_chroma(), hct.get_tone()) {
+  hue_ = hct.get_hue();
+  chroma_ = hct.get_chroma();
+}
+
+TonalPalette::TonalPalette(double hue, double chroma)
+    : key_color_(hue, chroma, 0.0) {
+  hue_ = hue;
+  chroma_ = chroma;
+  key_color_ = KeyColor(hue, chroma).create();
+}
+
+TonalPalette::TonalPalette(double hue, double chroma, Hct key_color)
+    : key_color_(key_color.get_hue(), key_color.get_chroma(),
+                 key_color.get_tone()) {
+  hue_ = hue;
+  chroma_ = chroma;
+}
+
+Argb TonalPalette::get(double tone) const {
+  return IntFromHcl(hue_, chroma_, tone);
+}
+
+KeyColor::KeyColor(double hue, double requested_chroma)
+    : hue_(hue), requested_chroma_(requested_chroma) {}
+
+Hct KeyColor::create() {
+  // Pivot around T50 because T50 has the most chroma available, on
+  // average. Thus it is most likely to have a direct answer.
+  const int pivot_tone = 50;
+  const int tone_step_size = 1;
+  // Epsilon to accept values slightly higher than the requested chroma.
+  const double epsilon = 0.01;
+
+  // Binary search to find the tone that can provide a chroma that is closest
+  // to the requested chroma.
+  int lower_tone = 0;
+  int upper_tone = 100;
+  while (lower_tone < upper_tone) {
+    const int mid_tone = (lower_tone + upper_tone) / 2;
+    bool is_ascending =
+        max_chroma(mid_tone) < max_chroma(mid_tone + tone_step_size);
+    bool sufficient_chroma =
+        max_chroma(mid_tone) >= requested_chroma_ - epsilon;
+
+    if (sufficient_chroma) {
+      // Either range [lower_tone, mid_tone] or [mid_tone, upper_tone] has
+      // the answer, so search in the range that is closer the pivot tone.
+      if (abs(lower_tone - pivot_tone) < abs(upper_tone - pivot_tone)) {
+        upper_tone = mid_tone;
+      } else {
+        if (lower_tone == mid_tone) {
+          return Hct(hue_, requested_chroma_, lower_tone);
+        }
+        lower_tone = mid_tone;
+      }
+    } else {
+      // As there's no sufficient chroma in the mid_tone, follow the direction
+      // to the chroma peak.
+      if (is_ascending) {
+        lower_tone = mid_tone + tone_step_size;
+      } else {
+        // Keep mid_tone for potential chroma peak.
+        upper_tone = mid_tone;
+      }
+    }
+  }
+
+  return Hct(hue_, requested_chroma_, lower_tone);
+}
+
+double KeyColor::max_chroma(double tone) {
+  auto it = chroma_cache_.find(tone);
+  if (it != chroma_cache_.end()) {
+    return it->second;
+  }
+
+  double chroma = Hct(hue_, max_chroma_value_, tone).get_chroma();
+  chroma_cache_[tone] = chroma;
+  return chroma;
+};
+
+}  // namespace material_color_utilities

third_party/material_color_utilities/cpp/palettes/tones.h

@@ -0,0 +1,78 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CPP_PALETTES_TONES_H_
+#define CPP_PALETTES_TONES_H_
+
+#include <unordered_map>
+
+#include "cpp/cam/hct.h"
+#include "cpp/utils/utils.h"
+
+namespace material_color_utilities {
+
+class TonalPalette {
+ public:
+  explicit TonalPalette(Argb argb);
+  TonalPalette(Hct hct);
+  TonalPalette(double hue, double chroma);
+  TonalPalette(double hue, double chroma, Hct key_color);
+
+  /**
+   * Returns the color for a given tone in this palette.
+   *
+   * @param tone 0.0 <= tone <= 100.0
+   * @return a color as an integer, in ARGB format.
+   */
+  Argb get(double tone) const;
+
+  double get_hue() const { return hue_; }
+  double get_chroma() const { return chroma_; }
+  Hct get_key_color() const { return key_color_; }
+
+ private:
+  double hue_;
+  double chroma_;
+  Hct key_color_;
+};
+
+/**
+ * Key color is a color that represents the hue and chroma of a tonal palette
+ */
+class KeyColor {
+ public:
+  KeyColor(double hue, double requested_chroma);
+  /**
+   * Creates a key color from a [hue] and a [chroma].
+   * The key color is the first tone, starting from T50, matching the given hue
+   * and chroma.
+   *
+   * @return Key color in Hct.
+   */
+  Hct create();
+
+ private:
+  const double max_chroma_value_ = 200.0;
+  double hue_;
+  double requested_chroma_;
+  // Cache that maps tone to max chroma to avoid duplicated HCT calculation.
+  std::unordered_map<double, double> chroma_cache_;
+
+  double max_chroma(double tone);
+};
+
+}  // namespace material_color_utilities
+#endif  // CPP_PALETTES_TONES_H_

third_party/material_color_utilities/cpp/quantize/celebi.cc

@@ -0,0 +1,60 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "cpp/quantize/celebi.h"
+
+#include <cstddef>
+#include <cstdio>
+#include <cstdlib>
+#include <vector>
+
+#include "cpp/quantize/wsmeans.h"
+#include "cpp/quantize/wu.h"
+#include "cpp/utils/utils.h"
+
+namespace material_color_utilities {
+
+QuantizerResult QuantizeCelebi(const std::vector<Argb>& pixels,
+                               uint16_t max_colors) {
+  if (max_colors == 0 || pixels.empty()) {
+    return QuantizerResult();
+  }
+
+  if (max_colors > 256) {
+    max_colors = 256;
+  }
+
+  int pixel_count = pixels.size();
+
+  std::vector<Argb> opaque_pixels;
+  opaque_pixels.reserve(pixel_count);
+  for (int i = 0; i < pixel_count; i++) {
+    int pixel = pixels[i];
+    if (!IsOpaque(pixel)) {
+      continue;
+    }
+    opaque_pixels.push_back(pixel);
+  }
+
+  std::vector<Argb> wu_result = QuantizeWu(opaque_pixels, max_colors);
+
+  QuantizerResult result =
+      QuantizeWsmeans(opaque_pixels, wu_result, max_colors);
+
+  return result;
+}
+
+}  // namespace material_color_utilities

third_party/material_color_utilities/cpp/quantize/celebi.h

@@ -0,0 +1,35 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CPP_QUANTIZE_CELEBI_H_
+#define CPP_QUANTIZE_CELEBI_H_
+
+#include <stdint.h>
+#include <stdlib.h>
+
+#include <vector>
+
+#include "cpp/quantize/wsmeans.h"
+#include "cpp/utils/utils.h"
+
+namespace material_color_utilities {
+
+QuantizerResult QuantizeCelebi(const std::vector<Argb>& pixels,
+                               uint16_t max_colors);
+
+}  // namespace material_color_utilities
+
+#endif  // CPP_QUANTIZE_CELEBI_H_

third_party/material_color_utilities/cpp/quantize/lab.cc

@@ -0,0 +1,96 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "cpp/quantize/lab.h"
+
+#include <math.h>
+
+#include "cpp/utils/utils.h"
+
+namespace material_color_utilities {
+
+Argb IntFromLab(const Lab lab) {
+  double e = 216.0 / 24389.0;
+  double kappa = 24389.0 / 27.0;
+  double ke = 8.0;
+
+  double fy = (lab.l + 16.0) / 116.0;
+  double fx = (lab.a / 500.0) + fy;
+  double fz = fy - (lab.b / 200.0);
+  double fx3 = fx * fx * fx;
+  double x_normalized = (fx3 > e) ? fx3 : (116.0 * fx - 16.0) / kappa;
+  double y_normalized = (lab.l > ke) ? fy * fy * fy : (lab.l / kappa);
+  double fz3 = fz * fz * fz;
+  double z_normalized = (fz3 > e) ? fz3 : (116.0 * fz - 16.0) / kappa;
+  double x = x_normalized * kWhitePointD65[0];
+  double y = y_normalized * kWhitePointD65[1];
+  double z = z_normalized * kWhitePointD65[2];
+
+  // intFromXyz
+  double rL = 3.2406 * x - 1.5372 * y - 0.4986 * z;
+  double gL = -0.9689 * x + 1.8758 * y + 0.0415 * z;
+  double bL = 0.0557 * x - 0.2040 * y + 1.0570 * z;
+
+  int red = Delinearized(rL);
+  int green = Delinearized(gL);
+  int blue = Delinearized(bL);
+
+  return ArgbFromRgb(red, green, blue);
+}
+
+Lab LabFromInt(const Argb argb) {
+  int red = (argb & 0x00ff0000) >> 16;
+  int green = (argb & 0x0000ff00) >> 8;
+  int blue = (argb & 0x000000ff);
+  double red_l = Linearized(red);
+  double green_l = Linearized(green);
+  double blue_l = Linearized(blue);
+  double x = 0.41233895 * red_l + 0.35762064 * green_l + 0.18051042 * blue_l;
+  double y = 0.2126 * red_l + 0.7152 * green_l + 0.0722 * blue_l;
+  double z = 0.01932141 * red_l + 0.11916382 * green_l + 0.95034478 * blue_l;
+  double y_normalized = y / kWhitePointD65[1];
+  double e = 216.0 / 24389.0;
+  double kappa = 24389.0 / 27.0;
+  double fy;
+  if (y_normalized > e) {
+    fy = pow(y_normalized, 1.0 / 3.0);
+  } else {
+    fy = (kappa * y_normalized + 16) / 116;
+  }
+
+  double x_normalized = x / kWhitePointD65[0];
+  double fx;
+  if (x_normalized > e) {
+    fx = pow(x_normalized, 1.0 / 3.0);
+  } else {
+    fx = (kappa * x_normalized + 16) / 116;
+  }
+
+  double z_normalized = z / kWhitePointD65[2];
+  double fz;
+  if (z_normalized > e) {
+    fz = pow(z_normalized, 1.0 / 3.0);
+  } else {
+    fz = (kappa * z_normalized + 16) / 116;
+  }
+
+  double l = 116.0 * fy - 16;
+  double a = 500.0 * (fx - fy);
+  double b = 200.0 * (fy - fz);
+  return {l, a, b};
+}
+
+}  // namespace material_color_utilities

third_party/material_color_utilities/cpp/quantize/lab.h

@@ -0,0 +1,57 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CPP_QUANTIZE_LAB_H_
+#define CPP_QUANTIZE_LAB_H_
+
+#include <algorithm>
+#include <cmath>
+#include <cstdint>
+#include <cstdlib>
+#include <map>
+#include <set>
+#include <string>
+#include <unordered_map>
+#include <unordered_set>
+#include <vector>
+
+#include "cpp/utils/utils.h"
+
+namespace material_color_utilities {
+
+struct Lab {
+  double l = 0.0;
+  double a = 0.0;
+  double b = 0.0;
+
+  double DeltaE(const Lab& lab) {
+    double d_l = l - lab.l;
+    double d_a = a - lab.a;
+    double d_b = b - lab.b;
+    return (d_l * d_l) + (d_a * d_a) + (d_b * d_b);
+  }
+
+  std::string ToString() {
+    return "Lab: L* " + std::to_string(l) + " a* " + std::to_string(a) +
+           " b* " + std::to_string(b);
+  }
+};
+
+Argb IntFromLab(const Lab lab);
+Lab LabFromInt(const Argb argb);
+
+}  // namespace material_color_utilities
+#endif  // CPP_QUANTIZE_LAB_H_

third_party/material_color_utilities/cpp/quantize/wsmeans.cc

@@ -0,0 +1,265 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "cpp/quantize/wsmeans.h"
+
+#include <algorithm>
+#include <cmath>
+#include <cstdint>
+#include <cstdlib>
+#include <map>
+#include <set>
+#include <string>
+#include <unordered_map>
+#include <unordered_set>
+#include <vector>
+
+#include "cpp/quantize/lab.h"
+
+constexpr int kMaxIterations = 100;
+constexpr double kMinDeltaE = 3.0;
+
+namespace material_color_utilities {
+
+struct Swatch {
+  Argb argb = 0;
+  int population = 0;
+
+  bool operator<(const Swatch& b) const { return population > b.population; }
+};
+
+struct DistanceToIndex {
+  double distance = 0.0;
+  int index = 0;
+
+  bool operator<(const DistanceToIndex& a) const {
+    return distance < a.distance;
+  }
+};
+
+QuantizerResult QuantizeWsmeans(const std::vector<Argb>& input_pixels,
+                                const std::vector<Argb>& starting_clusters,
+                                uint16_t max_colors) {
+  if (max_colors == 0 || input_pixels.empty()) {
+    return QuantizerResult();
+  }
+
+  if (max_colors > 256) {
+    // If colors is outside the range, just set it the max.
+    max_colors = 256;
+  }
+
+  uint32_t pixel_count = input_pixels.size();
+  std::unordered_map<Argb, int> pixel_to_count;
+  std::vector<uint32_t> pixels;
+  pixels.reserve(pixel_count);
+  std::vector<Lab> points;
+  points.reserve(pixel_count);
+  for (Argb pixel : input_pixels) {
+    // tested over 1000 runs with 128 colors, 12544 (112 x 112)
+    // std::map 10.9 ms
+    // std::unordered_map 10.2 ms
+    // absl::btree_map 9.0 ms
+    // absl::flat_hash_map 8.0 ms
+    std::unordered_map<Argb, int>::iterator it = pixel_to_count.find(pixel);
+    if (it != pixel_to_count.end()) {
+      it->second++;
+
+    } else {
+      pixels.push_back(pixel);
+      points.push_back(LabFromInt(pixel));
+      pixel_to_count[pixel] = 1;
+    }
+  }
+
+  int cluster_count = std::min((int)max_colors, (int)points.size());
+
+  if (!starting_clusters.empty()) {
+    cluster_count = std::min(cluster_count, (int)starting_clusters.size());
+  }
+
+  int pixel_count_sums[256] = {};
+  std::vector<Lab> clusters;
+  clusters.reserve(starting_clusters.size());
+  for (int argb : starting_clusters) {
+    clusters.push_back(LabFromInt(argb));
+  }
+
+  srand(42688);
+  int additional_clusters_needed = cluster_count - clusters.size();
+  if (starting_clusters.empty() && additional_clusters_needed > 0) {
+    for (int i = 0; i < additional_clusters_needed; i++) {
+      // Adds a random Lab color to clusters.
+      double l = rand() / (static_cast<double>(RAND_MAX)) * (100.0) + 0.0;
+      double a =
+          rand() / (static_cast<double>(RAND_MAX)) * (100.0 - -100.0) - 100.0;
+      double b =
+          rand() / (static_cast<double>(RAND_MAX)) * (100.0 - -100.0) - 100.0;
+      clusters.push_back({l, a, b});
+    }
+  }
+
+  std::vector<int> cluster_indices;
+  cluster_indices.reserve(points.size());
+
+  srand(42688);
+  for (size_t i = 0; i < points.size(); i++) {
+    cluster_indices.push_back(rand() % cluster_count);
+  }
+
+  std::vector<std::vector<int>> index_matrix(
+      cluster_count, std::vector<int>(cluster_count, 0));
+
+  std::vector<std::vector<DistanceToIndex>> distance_to_index_matrix(
+      cluster_count, std::vector<DistanceToIndex>(cluster_count));
+
+  for (int iteration = 0; iteration < kMaxIterations; iteration++) {
+    // Calculate cluster distances
+    for (int i = 0; i < cluster_count; i++) {
+      distance_to_index_matrix[i][i].distance = 0;
+      distance_to_index_matrix[i][i].index = i;
+      for (int j = i + 1; j < cluster_count; j++) {
+        double distance = clusters[i].DeltaE(clusters[j]);
+
+        distance_to_index_matrix[j][i].distance = distance;
+        distance_to_index_matrix[j][i].index = i;
+        distance_to_index_matrix[i][j].distance = distance;
+        distance_to_index_matrix[i][j].index = j;
+      }
+
+      std::vector<DistanceToIndex> row = distance_to_index_matrix[i];
+      std::sort(row.begin(), row.end());
+
+      for (int j = 0; j < cluster_count; j++) {
+        index_matrix[i][j] = row[j].index;
+      }
+    }
+
+    // Reassign points
+    bool color_moved = false;
+    for (size_t i = 0; i < points.size(); i++) {
+      Lab point = points[i];
+
+      int previous_cluster_index = cluster_indices[i];
+      Lab previous_cluster = clusters[previous_cluster_index];
+      double previous_distance = point.DeltaE(previous_cluster);
+      double minimum_distance = previous_distance;
+      int new_cluster_index = -1;
+
+      for (int j = 0; j < cluster_count; j++) {
+        if (distance_to_index_matrix[previous_cluster_index][j].distance >=
+            4 * previous_distance) {
+          continue;
+        }
+        double distance = point.DeltaE(clusters[j]);
+        if (distance < minimum_distance) {
+          minimum_distance = distance;
+          new_cluster_index = j;
+        }
+      }
+      if (new_cluster_index != -1) {
+        double distanceChange =
+            abs(sqrt(minimum_distance) - sqrt(previous_distance));
+        if (distanceChange > kMinDeltaE) {
+          color_moved = true;
+          cluster_indices[i] = new_cluster_index;
+        }
+      }
+    }
+
+    if (!color_moved && (iteration != 0)) {
+      break;
+    }
+
+    // Recalculate cluster centers
+    double component_a_sums[256] = {};
+    double component_b_sums[256] = {};
+    double component_c_sums[256] = {};
+    for (int i = 0; i < cluster_count; i++) {
+      pixel_count_sums[i] = 0;
+    }
+
+    for (size_t i = 0; i < points.size(); i++) {
+      int clusterIndex = cluster_indices[i];
+      Lab point = points[i];
+      int count = pixel_to_count[pixels[i]];
+
+      pixel_count_sums[clusterIndex] += count;
+      component_a_sums[clusterIndex] += (point.l * count);
+      component_b_sums[clusterIndex] += (point.a * count);
+      component_c_sums[clusterIndex] += (point.b * count);
+    }
+
+    for (int i = 0; i < cluster_count; i++) {
+      int count = pixel_count_sums[i];
+      if (count == 0) {
+        clusters[i] = {0, 0, 0};
+        continue;
+      }
+      double a = component_a_sums[i] / count;
+      double b = component_b_sums[i] / count;
+      double c = component_c_sums[i] / count;
+      clusters[i] = {a, b, c};
+    }
+  }
+
+  std::vector<Swatch> swatches;
+  std::vector<Argb> cluster_argbs;
+  std::vector<Argb> all_cluster_argbs;
+  for (int i = 0; i < cluster_count; i++) {
+    Argb possible_new_cluster = IntFromLab(clusters[i]);
+    all_cluster_argbs.push_back(possible_new_cluster);
+
+    int count = pixel_count_sums[i];
+    if (count == 0) {
+      continue;
+    }
+    int use_new_cluster = 1;
+    for (size_t j = 0; j < swatches.size(); j++) {
+      if (swatches[j].argb == possible_new_cluster) {
+        swatches[j].population += count;
+        use_new_cluster = 0;
+        break;
+      }
+    }
+
+    if (use_new_cluster == 0) {
+      continue;
+    }
+    cluster_argbs.push_back(possible_new_cluster);
+    swatches.push_back({possible_new_cluster, count});
+  }
+  std::sort(swatches.begin(), swatches.end());
+
+  // Constructs the quantizer result to return.
+
+  std::map<Argb, uint32_t> color_to_count;
+  for (size_t i = 0; i < swatches.size(); i++) {
+    color_to_count[swatches[i].argb] = swatches[i].population;
+  }
+
+  std::map<Argb, Argb> input_pixel_to_cluster_pixel;
+  for (size_t i = 0; i < points.size(); i++) {
+    int pixel = pixels[i];
+    int cluster_index = cluster_indices[i];
+    int cluster_argb = all_cluster_argbs[cluster_index];
+    input_pixel_to_cluster_pixel[pixel] = cluster_argb;
+  }
+
+  return {color_to_count, input_pixel_to_cluster_pixel};
+}
+
+}  // namespace material_color_utilities

third_party/material_color_utilities/cpp/quantize/wsmeans.h

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CPP_QUANTIZE_WSMEANS_H_
+#define CPP_QUANTIZE_WSMEANS_H_
+#include <stdint.h>
+
+#include <map>
+#include <vector>
+
+#include "cpp/utils/utils.h"
+
+namespace material_color_utilities {
+
+struct QuantizerResult {
+  std::map<Argb, uint32_t> color_to_count;
+  std::map<Argb, Argb> input_pixel_to_cluster_pixel;
+};
+
+QuantizerResult QuantizeWsmeans(const std::vector<Argb>& input_pixels,
+                                const std::vector<Argb>& starting_clusters,
+                                uint16_t max_colors);
+}  // namespace material_color_utilities
+
+#endif  // CPP_QUANTIZE_WSMEANS_H_

third_party/material_color_utilities/cpp/quantize/wu.cc

@@ -0,0 +1,357 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "cpp/quantize/wu.h"
+
+#include <stdlib.h>
+
+#include <cassert>
+#include <cstdint>
+#include <cstdio>
+#include <vector>
+
+#include "cpp/utils/utils.h"
+
+namespace material_color_utilities {
+
+struct Box {
+  int r0 = 0;
+  int r1 = 0;
+  int g0 = 0;
+  int g1 = 0;
+  int b0 = 0;
+  int b1 = 0;
+  int vol = 0;
+};
+
+enum class Direction {
+  kRed,
+  kGreen,
+  kBlue,
+};
+
+constexpr int kIndexBits = 5;
+constexpr int kIndexCount = ((1 << kIndexBits) + 1);
+constexpr int kTotalSize = (kIndexCount * kIndexCount * kIndexCount);
+constexpr int kMaxColors = 256;
+
+using IntArray = std::vector<int64_t>;
+using DoubleArray = std::vector<double>;
+
+int GetIndex(int r, int g, int b) {
+  return (r << (kIndexBits * 2)) + (r << (kIndexBits + 1)) + (g << kIndexBits) +
+         r + g + b;
+}
+
+void ConstructHistogram(const std::vector<Argb>& pixels, IntArray& weights,
+                        IntArray& m_r, IntArray& m_g, IntArray& m_b,
+                        DoubleArray& moments) {
+  for (size_t i = 0; i < pixels.size(); i++) {
+    Argb pixel = pixels[i];
+    int red = RedFromInt(pixel);
+    int green = GreenFromInt(pixel);
+    int blue = BlueFromInt(pixel);
+
+    int bits_to_remove = 8 - kIndexBits;
+    int index_r = (red >> bits_to_remove) + 1;
+    int index_g = (green >> bits_to_remove) + 1;
+    int index_b = (blue >> bits_to_remove) + 1;
+    int index = GetIndex(index_r, index_g, index_b);
+
+    weights[index]++;
+    m_r[index] += red;
+    m_g[index] += green;
+    m_b[index] += blue;
+    moments[index] += (red * red) + (green * green) + (blue * blue);
+  }
+}
+
+void ComputeMoments(IntArray& weights, IntArray& m_r, IntArray& m_g,
+                    IntArray& m_b, DoubleArray& moments) {
+  for (int r = 1; r < kIndexCount; r++) {
+    int64_t area[kIndexCount] = {};
+    int64_t area_r[kIndexCount] = {};
+    int64_t area_g[kIndexCount] = {};
+    int64_t area_b[kIndexCount] = {};
+    double area_2[kIndexCount] = {};
+    for (int g = 1; g < kIndexCount; g++) {
+      int64_t line = 0;
+      int64_t line_r = 0;
+      int64_t line_g = 0;
+      int64_t line_b = 0;
+      double line_2 = 0.0;
+      for (int b = 1; b < kIndexCount; b++) {
+        int index = GetIndex(r, g, b);
+        line += weights[index];
+        line_r += m_r[index];
+        line_g += m_g[index];
+        line_b += m_b[index];
+        line_2 += moments[index];
+
+        area[b] += line;
+        area_r[b] += line_r;
+        area_g[b] += line_g;
+        area_b[b] += line_b;
+        area_2[b] += line_2;
+
+        int previous_index = GetIndex(r - 1, g, b);
+        weights[index] = weights[previous_index] + area[b];
+        m_r[index] = m_r[previous_index] + area_r[b];
+        m_g[index] = m_g[previous_index] + area_g[b];
+        m_b[index] = m_b[previous_index] + area_b[b];
+        moments[index] = moments[previous_index] + area_2[b];
+      }
+    }
+  }
+}
+
+int64_t Top(const Box& cube, const Direction direction, const int position,
+            const IntArray& moment) {
+  if (direction == Direction::kRed) {
+    return (moment[GetIndex(position, cube.g1, cube.b1)] -
+            moment[GetIndex(position, cube.g1, cube.b0)] -
+            moment[GetIndex(position, cube.g0, cube.b1)] +
+            moment[GetIndex(position, cube.g0, cube.b0)]);
+  } else if (direction == Direction::kGreen) {
+    return (moment[GetIndex(cube.r1, position, cube.b1)] -
+            moment[GetIndex(cube.r1, position, cube.b0)] -
+            moment[GetIndex(cube.r0, position, cube.b1)] +
+            moment[GetIndex(cube.r0, position, cube.b0)]);
+  } else {
+    return (moment[GetIndex(cube.r1, cube.g1, position)] -
+            moment[GetIndex(cube.r1, cube.g0, position)] -
+            moment[GetIndex(cube.r0, cube.g1, position)] +
+            moment[GetIndex(cube.r0, cube.g0, position)]);
+  }
+}
+
+int64_t Bottom(const Box& cube, const Direction direction,
+               const IntArray& moment) {
+  if (direction == Direction::kRed) {
+    return (-moment[GetIndex(cube.r0, cube.g1, cube.b1)] +
+            moment[GetIndex(cube.r0, cube.g1, cube.b0)] +
+            moment[GetIndex(cube.r0, cube.g0, cube.b1)] -
+            moment[GetIndex(cube.r0, cube.g0, cube.b0)]);
+  } else if (direction == Direction::kGreen) {
+    return (-moment[GetIndex(cube.r1, cube.g0, cube.b1)] +
+            moment[GetIndex(cube.r1, cube.g0, cube.b0)] +
+            moment[GetIndex(cube.r0, cube.g0, cube.b1)] -
+            moment[GetIndex(cube.r0, cube.g0, cube.b0)]);
+  } else {
+    return (-moment[GetIndex(cube.r1, cube.g1, cube.b0)] +
+            moment[GetIndex(cube.r1, cube.g0, cube.b0)] +
+            moment[GetIndex(cube.r0, cube.g1, cube.b0)] -
+            moment[GetIndex(cube.r0, cube.g0, cube.b0)]);
+  }
+}
+
+int64_t Vol(const Box& cube, const IntArray& moment) {
+  return (moment[GetIndex(cube.r1, cube.g1, cube.b1)] -
+          moment[GetIndex(cube.r1, cube.g1, cube.b0)] -
+          moment[GetIndex(cube.r1, cube.g0, cube.b1)] +
+          moment[GetIndex(cube.r1, cube.g0, cube.b0)] -
+          moment[GetIndex(cube.r0, cube.g1, cube.b1)] +
+          moment[GetIndex(cube.r0, cube.g1, cube.b0)] +
+          moment[GetIndex(cube.r0, cube.g0, cube.b1)] -
+          moment[GetIndex(cube.r0, cube.g0, cube.b0)]);
+}
+
+double Variance(const Box& cube, const IntArray& weights, const IntArray& m_r,
+                const IntArray& m_g, const IntArray& m_b,
+                const DoubleArray& moments) {
+  double dr = Vol(cube, m_r);
+  double dg = Vol(cube, m_g);
+  double db = Vol(cube, m_b);
+  double xx = moments[GetIndex(cube.r1, cube.g1, cube.b1)] -
+              moments[GetIndex(cube.r1, cube.g1, cube.b0)] -
+              moments[GetIndex(cube.r1, cube.g0, cube.b1)] +
+              moments[GetIndex(cube.r1, cube.g0, cube.b0)] -
+              moments[GetIndex(cube.r0, cube.g1, cube.b1)] +
+              moments[GetIndex(cube.r0, cube.g1, cube.b0)] +
+              moments[GetIndex(cube.r0, cube.g0, cube.b1)] -
+              moments[GetIndex(cube.r0, cube.g0, cube.b0)];
+  double hypotenuse = dr * dr + dg * dg + db * db;
+  double volume = Vol(cube, weights);
+  return xx - hypotenuse / volume;
+}
+
+double Maximize(const Box& cube, const Direction direction, const int first,
+                const int last, int* cut, const int64_t whole_w,
+                const int64_t whole_r, const int64_t whole_g,
+                const int64_t whole_b, const IntArray& weights,
+                const IntArray& m_r, const IntArray& m_g, const IntArray& m_b) {
+  int64_t bottom_r = Bottom(cube, direction, m_r);
+  int64_t bottom_g = Bottom(cube, direction, m_g);
+  int64_t bottom_b = Bottom(cube, direction, m_b);
+  int64_t bottom_w = Bottom(cube, direction, weights);
+
+  double max = 0.0;
+  *cut = -1;
+
+  int64_t half_r, half_g, half_b, half_w;
+  for (int i = first; i < last; i++) {
+    half_r = bottom_r + Top(cube, direction, i, m_r);
+    half_g = bottom_g + Top(cube, direction, i, m_g);
+    half_b = bottom_b + Top(cube, direction, i, m_b);
+    half_w = bottom_w + Top(cube, direction, i, weights);
+    if (half_w == 0) {
+      continue;
+    }
+
+    double temp = (static_cast<double>(half_r) * half_r +
+                   static_cast<double>(half_g) * half_g +
+                   static_cast<double>(half_b) * half_b) /
+                  static_cast<double>(half_w);
+
+    half_r = whole_r - half_r;
+    half_g = whole_g - half_g;
+    half_b = whole_b - half_b;
+    half_w = whole_w - half_w;
+    if (half_w == 0) {
+      continue;
+    }
+    temp += (static_cast<double>(half_r) * half_r +
+             static_cast<double>(half_g) * half_g +
+             static_cast<double>(half_b) * half_b) /
+            static_cast<double>(half_w);
+
+    if (temp > max) {
+      max = temp;
+      *cut = i;
+    }
+  }
+  return max;
+}
+
+bool Cut(Box& box1, Box& box2, const IntArray& weights, const IntArray& m_r,
+         const IntArray& m_g, const IntArray& m_b) {
+  int64_t whole_r = Vol(box1, m_r);
+  int64_t whole_g = Vol(box1, m_g);
+  int64_t whole_b = Vol(box1, m_b);
+  int64_t whole_w = Vol(box1, weights);
+
+  int cut_r, cut_g, cut_b;
+  double max_r =
+      Maximize(box1, Direction::kRed, box1.r0 + 1, box1.r1, &cut_r, whole_w,
+               whole_r, whole_g, whole_b, weights, m_r, m_g, m_b);
+  double max_g =
+      Maximize(box1, Direction::kGreen, box1.g0 + 1, box1.g1, &cut_g, whole_w,
+               whole_r, whole_g, whole_b, weights, m_r, m_g, m_b);
+  double max_b =
+      Maximize(box1, Direction::kBlue, box1.b0 + 1, box1.b1, &cut_b, whole_w,
+               whole_r, whole_g, whole_b, weights, m_r, m_g, m_b);
+
+  Direction direction;
+  if (max_r >= max_g && max_r >= max_b) {
+    direction = Direction::kRed;
+    if (cut_r < 0) {
+      return false;
+    }
+  } else if (max_g >= max_r && max_g >= max_b) {
+    direction = Direction::kGreen;
+  } else {
+    direction = Direction::kBlue;
+  }
+
+  box2.r1 = box1.r1;
+  box2.g1 = box1.g1;
+  box2.b1 = box1.b1;
+
+  if (direction == Direction::kRed) {
+    box2.r0 = box1.r1 = cut_r;
+    box2.g0 = box1.g0;
+    box2.b0 = box1.b0;
+  } else if (direction == Direction::kGreen) {
+    box2.r0 = box1.r0;
+    box2.g0 = box1.g1 = cut_g;
+    box2.b0 = box1.b0;
+  } else {
+    box2.r0 = box1.r0;
+    box2.g0 = box1.g0;
+    box2.b0 = box1.b1 = cut_b;
+  }
+
+  box1.vol = (box1.r1 - box1.r0) * (box1.g1 - box1.g0) * (box1.b1 - box1.b0);
+  box2.vol = (box2.r1 - box2.r0) * (box2.g1 - box2.g0) * (box2.b1 - box2.b0);
+  return true;
+}
+
+std::vector<Argb> QuantizeWu(const std::vector<Argb>& pixels,
+                             uint16_t max_colors) {
+  if (max_colors <= 0 || max_colors > 256 || pixels.empty()) {
+    return std::vector<Argb>();
+  }
+
+  IntArray weights(kTotalSize, 0);
+  IntArray moments_red(kTotalSize, 0);
+  IntArray moments_green(kTotalSize, 0);
+  IntArray moments_blue(kTotalSize, 0);
+  DoubleArray moments(kTotalSize, 0.0);
+  ConstructHistogram(pixels, weights, moments_red, moments_green, moments_blue,
+                     moments);
+  ComputeMoments(weights, moments_red, moments_green, moments_blue, moments);
+
+  std::vector<Box> cubes(kMaxColors);
+  cubes[0].r0 = cubes[0].g0 = cubes[0].b0 = 0;
+  cubes[0].r1 = cubes[0].g1 = cubes[0].b1 = kIndexCount - 1;
+
+  std::vector<double> volume_variance(kMaxColors);
+  int next = 0;
+  for (int i = 1; i < max_colors; ++i) {
+    if (Cut(cubes[next], cubes[i], weights, moments_red, moments_green,
+            moments_blue)) {
+      volume_variance[next] =
+          cubes[next].vol > 1 ? Variance(cubes[next], weights, moments_red,
+                                         moments_green, moments_blue, moments)
+                              : 0.0;
+      volume_variance[i] = cubes[i].vol > 1
+                               ? Variance(cubes[i], weights, moments_red,
+                                          moments_green, moments_blue, moments)
+                               : 0.0;
+    } else {
+      volume_variance[next] = 0.0;
+      i--;
+    }
+
+    next = 0;
+    double temp = volume_variance[0];
+    for (int j = 1; j <= i; j++) {
+      if (volume_variance[j] > temp) {
+        temp = volume_variance[j];
+        next = j;
+      }
+    }
+    if (temp <= 0.0) {
+      max_colors = i + 1;
+      break;
+    }
+  }
+
+  std::vector<Argb> out_colors;
+  for (int i = 0; i < max_colors; ++i) {
+    int64_t weight = Vol(cubes[i], weights);
+    if (weight > 0) {
+      int32_t red = Vol(cubes[i], moments_red) / weight;
+      int32_t green = Vol(cubes[i], moments_green) / weight;
+      int32_t blue = Vol(cubes[i], moments_blue) / weight;
+      uint32_t argb = ArgbFromRgb(red, green, blue);
+      out_colors.push_back(argb);
+    }
+  }
+
+  return out_colors;
+}
+}  // namespace material_color_utilities

third_party/material_color_utilities/cpp/quantize/wu.h

@@ -0,0 +1,31 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CPP_QUANTIZE_WU_H_
+#define CPP_QUANTIZE_WU_H_
+
+#include <stdint.h>
+
+#include <vector>
+
+#include "cpp/utils/utils.h"
+
+namespace material_color_utilities {
+
+std::vector<Argb> QuantizeWu(const std::vector<Argb>& pixels,
+                             uint16_t max_colors);
+}
+#endif  // CPP_QUANTIZE_WU_H_

third_party/material_color_utilities/cpp/scheme/scheme_content.cc

@@ -0,0 +1,58 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "cpp/scheme/scheme_content.h"
+
+#include <cmath>
+
+#include "cpp/cam/hct.h"
+#include "cpp/dislike/dislike.h"
+#include "cpp/dynamiccolor/dynamic_scheme.h"
+#include "cpp/dynamiccolor/variant.h"
+#include "cpp/palettes/tones.h"
+#include "cpp/temperature/temperature_cache.h"
+
+namespace material_color_utilities {
+
+SchemeContent::SchemeContent(Hct set_source_color_hct, bool set_is_dark,
+                             double set_contrast_level)
+    : DynamicScheme(
+          /*set_source_color_hct:*/ set_source_color_hct,
+          /*variant:*/ Variant::kContent,
+          /*contrast_level:*/ set_contrast_level,
+          /*is_dark:*/ set_is_dark,
+          /*primary_palette:*/
+          TonalPalette(set_source_color_hct.get_hue(),
+                       set_source_color_hct.get_chroma()),
+          /*secondary_palette:*/
+          TonalPalette(set_source_color_hct.get_hue(),
+                       fmax(set_source_color_hct.get_chroma() - 32.0,
+                            set_source_color_hct.get_chroma() * 0.5)),
+          /*tertiary_palette:*/
+          TonalPalette(FixIfDisliked(TemperatureCache(set_source_color_hct)
+                                         .GetAnalogousColors(3, 6)
+                                         .at(2))),
+          /*neutral_palette:*/
+          TonalPalette(set_source_color_hct.get_hue(),
+                       set_source_color_hct.get_chroma() / 8.0),
+          /*neutral_variant_palette:*/
+          TonalPalette(set_source_color_hct.get_hue(),
+                       set_source_color_hct.get_chroma() / 8.0 + 4.0)) {}
+
+SchemeContent::SchemeContent(Hct set_source_color_hct, bool set_is_dark)
+    : SchemeContent::SchemeContent(set_source_color_hct, set_is_dark, 0.0) {}
+
+}  // namespace material_color_utilities

third_party/material_color_utilities/cpp/scheme/scheme_content.h

@@ -0,0 +1,33 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CPP_SCHEME_SCHEME_CONTENT_H_
+#define CPP_SCHEME_SCHEME_CONTENT_H_
+
+#include "cpp/cam/hct.h"
+#include "cpp/dynamiccolor/dynamic_scheme.h"
+
+namespace material_color_utilities {
+
+struct SchemeContent : public DynamicScheme {
+  SchemeContent(Hct set_source_color_hct, bool set_is_dark,
+                double set_contrast_level);
+  SchemeContent(Hct set_source_color_hct, bool set_is_dark);
+};
+
+}  // namespace material_color_utilities
+
+#endif  // CPP_SCHEME_SCHEME_CONTENT_H_

third_party/material_color_utilities/cpp/scheme/scheme_expressive.cc

@@ -0,0 +1,62 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "cpp/scheme/scheme_expressive.h"
+
+#include <vector>
+
+#include "cpp/cam/hct.h"
+#include "cpp/dynamiccolor/dynamic_scheme.h"
+#include "cpp/dynamiccolor/variant.h"
+#include "cpp/palettes/tones.h"
+
+namespace material_color_utilities {
+
+const std::vector<double> kHues = {0, 21, 51, 121, 151, 191, 271, 321, 360};
+
+const std::vector<double> kSecondaryRotations = {45, 95, 45, 20, 45,
+                                                 90, 45, 45, 45};
+
+const std::vector<double> kTertiaryRotations = {120, 120, 20,  45, 20,
+                                                15,  20,  120, 120};
+
+SchemeExpressive::SchemeExpressive(Hct set_source_color_hct, bool set_is_dark,
+                                   double set_contrast_level)
+    : DynamicScheme(
+          /*set_source_color_hct:*/ set_source_color_hct,
+          /*variant:*/ Variant::kExpressive,
+          /*contrast_level:*/ set_contrast_level,
+          /*is_dark:*/ set_is_dark,
+          /*primary_palette:*/
+          TonalPalette(set_source_color_hct.get_hue() + 240.0, 40.0),
+          /*secondary_palette:*/
+          TonalPalette(DynamicScheme::GetRotatedHue(set_source_color_hct, kHues,
+                                                    kSecondaryRotations),
+                       24.0),
+          /*tertiary_palette:*/
+          TonalPalette(DynamicScheme::GetRotatedHue(set_source_color_hct, kHues,
+                                                    kTertiaryRotations),
+                       32.0),
+          /*neutral_palette:*/
+          TonalPalette(set_source_color_hct.get_hue() + 15.0, 8.0),
+          /*neutral_variant_palette:*/
+          TonalPalette(set_source_color_hct.get_hue() + 15, 12.0)) {}
+
+SchemeExpressive::SchemeExpressive(Hct set_source_color_hct, bool set_is_dark)
+    : SchemeExpressive::SchemeExpressive(set_source_color_hct, set_is_dark,
+                                         0.0) {}
+
+}  // namespace material_color_utilities

third_party/material_color_utilities/cpp/scheme/scheme_expressive.h

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CPP_SCHEME_SCHEME_EXPRESSIVE_H_
+#define CPP_SCHEME_SCHEME_EXPRESSIVE_H_
+
+#include "cpp/cam/hct.h"
+#include "cpp/dynamiccolor/dynamic_scheme.h"
+
+namespace material_color_utilities {
+
+struct SchemeExpressive : public DynamicScheme {
+  SchemeExpressive(Hct source_color_hct, bool is_dark, double contrast_level);
+  SchemeExpressive(Hct source_color_hct, bool is_dark);
+};
+
+}  // namespace material_color_utilities
+
+#endif  // CPP_SCHEME_SCHEME_EXPRESSIVE_H_

third_party/material_color_utilities/cpp/scheme/scheme_fidelity.cc

@@ -0,0 +1,57 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "cpp/scheme/scheme_fidelity.h"
+
+#include <cmath>
+
+#include "cpp/cam/hct.h"
+#include "cpp/dislike/dislike.h"
+#include "cpp/dynamiccolor/dynamic_scheme.h"
+#include "cpp/dynamiccolor/variant.h"
+#include "cpp/palettes/tones.h"
+#include "cpp/temperature/temperature_cache.h"
+
+namespace material_color_utilities {
+
+SchemeFidelity::SchemeFidelity(Hct set_source_color_hct, bool set_is_dark,
+                               double set_contrast_level)
+    : DynamicScheme(
+          /*set_source_color_hct:*/ set_source_color_hct,
+          /*variant:*/ Variant::kFidelity,
+          /*contrast_level:*/ set_contrast_level,
+          /*is_dark:*/ set_is_dark,
+          /*primary_palette:*/
+          TonalPalette(set_source_color_hct.get_hue(),
+                       set_source_color_hct.get_chroma()),
+          /*secondary_palette:*/
+          TonalPalette(set_source_color_hct.get_hue(),
+                       fmax(set_source_color_hct.get_chroma() - 32.0,
+                            set_source_color_hct.get_chroma() * 0.5)),
+          /*tertiary_palette:*/
+          TonalPalette(FixIfDisliked(
+              TemperatureCache(set_source_color_hct).GetComplement())),
+          /*neutral_palette:*/
+          TonalPalette(set_source_color_hct.get_hue(),
+                       set_source_color_hct.get_chroma() / 8.0),
+          /*neutral_variant_palette:*/
+          TonalPalette(set_source_color_hct.get_hue(),
+                       set_source_color_hct.get_chroma() / 8.0 + 4.0)) {}
+
+SchemeFidelity::SchemeFidelity(Hct set_source_color_hct, bool set_is_dark)
+    : SchemeFidelity::SchemeFidelity(set_source_color_hct, set_is_dark, 0.0) {}
+
+}  // namespace material_color_utilities

third_party/material_color_utilities/cpp/scheme/scheme_fidelity.h

@@ -0,0 +1,33 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CPP_SCHEME_SCHEME_FIDELITY_H_
+#define CPP_SCHEME_SCHEME_FIDELITY_H_
+
+#include "cpp/cam/hct.h"
+#include "cpp/dynamiccolor/dynamic_scheme.h"
+
+namespace material_color_utilities {
+
+struct SchemeFidelity : public DynamicScheme {
+  SchemeFidelity(Hct set_source_color_hct, bool set_is_dark,
+                 double set_contrast_level);
+  SchemeFidelity(Hct set_source_color_hct, bool set_is_dark);
+};
+
+}  // namespace material_color_utilities
+
+#endif  // CPP_SCHEME_SCHEME_FIDELITY_H_

third_party/material_color_utilities/cpp/scheme/scheme_fruit_salad.cc

@@ -0,0 +1,52 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "cpp/scheme/scheme_fruit_salad.h"
+
+#include "cpp/cam/hct.h"
+#include "cpp/dynamiccolor/dynamic_scheme.h"
+#include "cpp/dynamiccolor/variant.h"
+#include "cpp/palettes/tones.h"
+
+namespace material_color_utilities {
+
+SchemeFruitSalad::SchemeFruitSalad(Hct set_source_color_hct, bool set_is_dark,
+                                   double set_contrast_level)
+    : DynamicScheme(
+          /*set_source_color_hct:*/ set_source_color_hct,
+          /*variant:*/ Variant::kFruitSalad,
+          /*contrast_level:*/ set_contrast_level,
+          /*is_dark:*/ set_is_dark,
+          /*primary_palette:*/
+          TonalPalette(
+              SanitizeDegreesDouble(set_source_color_hct.get_hue() - 50.0),
+              48.0),
+          /*secondary_palette:*/
+          TonalPalette(
+              SanitizeDegreesDouble(set_source_color_hct.get_hue() - 50.0),
+              36.0),
+          /*tertiary_palette:*/
+          TonalPalette(set_source_color_hct.get_hue(), 36.0),
+          /*neutral_palette:*/
+          TonalPalette(set_source_color_hct.get_hue(), 10.0),
+          /*neutral_variant_palette:*/
+          TonalPalette(set_source_color_hct.get_hue(), 16.0)) {}
+
+SchemeFruitSalad::SchemeFruitSalad(Hct set_source_color_hct, bool set_is_dark)
+    : SchemeFruitSalad::SchemeFruitSalad(set_source_color_hct, set_is_dark,
+                                         0.0) {}
+
+}  // namespace material_color_utilities

third_party/material_color_utilities/cpp/scheme/scheme_fruit_salad.h

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CPP_SCHEME_SCHEME_FRUIT_SALAD_H_
+#define CPP_SCHEME_SCHEME_FRUIT_SALAD_H_
+
+#include "cpp/cam/hct.h"
+#include "cpp/dynamiccolor/dynamic_scheme.h"
+
+namespace material_color_utilities {
+
+struct SchemeFruitSalad : public DynamicScheme {
+  SchemeFruitSalad(Hct source_color_hct, bool is_dark, double contrast_level);
+  SchemeFruitSalad(Hct source_color_hct, bool is_dark);
+};
+
+}  // namespace material_color_utilities
+
+#endif  // CPP_SCHEME_SCHEME_FRUIT_SALAD_H_

third_party/material_color_utilities/cpp/scheme/scheme_monochrome.cc

@@ -0,0 +1,48 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "cpp/scheme/scheme_monochrome.h"
+
+#include "cpp/cam/hct.h"
+#include "cpp/dynamiccolor/dynamic_scheme.h"
+#include "cpp/dynamiccolor/variant.h"
+#include "cpp/palettes/tones.h"
+
+namespace material_color_utilities {
+
+SchemeMonochrome::SchemeMonochrome(Hct set_source_color_hct, bool set_is_dark,
+                                   double set_contrast_level)
+    : DynamicScheme(
+          /*set_source_color_hct:*/ set_source_color_hct,
+          /*variant:*/ Variant::kMonochrome,
+          /*contrast_level:*/ set_contrast_level,
+          /*is_dark:*/ set_is_dark,
+          /*primary_palette:*/
+          TonalPalette(set_source_color_hct.get_hue(), 0.0),
+          /*secondary_palette:*/
+          TonalPalette(set_source_color_hct.get_hue(), 0.0),
+          /*tertiary_palette:*/
+          TonalPalette(set_source_color_hct.get_hue(), 0.0),
+          /*neutral_palette:*/
+          TonalPalette(set_source_color_hct.get_hue(), 0.0),
+          /*neutral_variant_palette:*/
+          TonalPalette(set_source_color_hct.get_hue(), 0.0)) {}
+
+SchemeMonochrome::SchemeMonochrome(Hct set_source_color_hct, bool set_is_dark)
+    : SchemeMonochrome::SchemeMonochrome(set_source_color_hct, set_is_dark,
+                                         0.0) {}
+
+}  // namespace material_color_utilities

third_party/material_color_utilities/cpp/scheme/scheme_monochrome.h

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CPP_SCHEME_SCHEME_MONOCHROME_H_
+#define CPP_SCHEME_SCHEME_MONOCHROME_H_
+
+#include "cpp/cam/hct.h"
+#include "cpp/dynamiccolor/dynamic_scheme.h"
+
+namespace material_color_utilities {
+
+struct SchemeMonochrome : public DynamicScheme {
+  SchemeMonochrome(Hct source_color_hct, bool is_dark, double contrast_level);
+  SchemeMonochrome(Hct source_color_hct, bool is_dark);
+};
+
+}  // namespace material_color_utilities
+
+#endif  // CPP_SCHEME_SCHEME_MONOCHROME_H_

third_party/material_color_utilities/cpp/scheme/scheme_neutral.cc

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "cpp/scheme/scheme_neutral.h"
+
+#include "cpp/cam/hct.h"
+#include "cpp/dynamiccolor/dynamic_scheme.h"
+#include "cpp/dynamiccolor/variant.h"
+#include "cpp/palettes/tones.h"
+
+namespace material_color_utilities {
+
+SchemeNeutral::SchemeNeutral(Hct set_source_color_hct, bool set_is_dark,
+                             double set_contrast_level)
+    : DynamicScheme(
+          /*set_source_color_hct:*/ set_source_color_hct,
+          /*variant:*/ Variant::kNeutral,
+          /*contrast_level:*/ set_contrast_level,
+          /*is_dark:*/ set_is_dark,
+          /*primary_palette:*/
+          TonalPalette(set_source_color_hct.get_hue(), 12.0),
+          /*secondary_palette:*/
+          TonalPalette(set_source_color_hct.get_hue(), 8.0),
+          /*tertiary_palette:*/
+          TonalPalette(set_source_color_hct.get_hue(), 16.0),
+          /*neutral_palette:*/
+          TonalPalette(set_source_color_hct.get_hue(), 2.0),
+          /*neutral_variant_palette:*/
+          TonalPalette(set_source_color_hct.get_hue(), 2.0)) {}
+
+SchemeNeutral::SchemeNeutral(Hct set_source_color_hct, bool set_is_dark)
+    : SchemeNeutral::SchemeNeutral(set_source_color_hct, set_is_dark, 0.0) {}
+
+}  // namespace material_color_utilities

third_party/material_color_utilities/cpp/scheme/scheme_neutral.h

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CPP_SCHEME_SCHEME_NEUTRAL_H_
+#define CPP_SCHEME_SCHEME_NEUTRAL_H_
+
+#include "cpp/cam/hct.h"
+#include "cpp/dynamiccolor/dynamic_scheme.h"
+
+namespace material_color_utilities {
+
+struct SchemeNeutral : public DynamicScheme {
+  SchemeNeutral(Hct source_color_hct, bool is_dark, double contrast_level);
+  SchemeNeutral(Hct source_color_hct, bool is_dark);
+};
+
+}  // namespace material_color_utilities
+
+#endif  // CPP_SCHEME_SCHEME_NEUTRAL_H_

third_party/material_color_utilities/cpp/scheme/scheme_rainbow.cc

@@ -0,0 +1,49 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "cpp/scheme/scheme_rainbow.h"
+
+#include "cpp/cam/hct.h"
+#include "cpp/dynamiccolor/dynamic_scheme.h"
+#include "cpp/dynamiccolor/variant.h"
+#include "cpp/palettes/tones.h"
+
+namespace material_color_utilities {
+
+SchemeRainbow::SchemeRainbow(Hct set_source_color_hct, bool set_is_dark,
+                             double set_contrast_level)
+    : DynamicScheme(
+          /*set_source_color_hct:*/ set_source_color_hct,
+          /*variant:*/ Variant::kRainbow,
+          /*contrast_level:*/ set_contrast_level,
+          /*is_dark:*/ set_is_dark,
+          /*primary_palette:*/
+          TonalPalette(set_source_color_hct.get_hue(), 48.0),
+          /*secondary_palette:*/
+          TonalPalette(set_source_color_hct.get_hue(), 16.0),
+          /*tertiary_palette:*/
+          TonalPalette(
+              SanitizeDegreesDouble(set_source_color_hct.get_hue() + 60.0),
+              24.0),
+          /*neutral_palette:*/
+          TonalPalette(set_source_color_hct.get_hue(), 0.0),
+          /*neutral_variant_palette:*/
+          TonalPalette(set_source_color_hct.get_hue(), 0.0)) {}
+
+SchemeRainbow::SchemeRainbow(Hct set_source_color_hct, bool set_is_dark)
+    : SchemeRainbow::SchemeRainbow(set_source_color_hct, set_is_dark, 0.0) {}
+
+}  // namespace material_color_utilities

third_party/material_color_utilities/cpp/scheme/scheme_rainbow.h

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CPP_SCHEME_SCHEME_RAINBOW_H_
+#define CPP_SCHEME_SCHEME_RAINBOW_H_
+
+#include "cpp/cam/hct.h"
+#include "cpp/dynamiccolor/dynamic_scheme.h"
+
+namespace material_color_utilities {
+
+struct SchemeRainbow : public DynamicScheme {
+  SchemeRainbow(Hct source_color_hct, bool is_dark, double contrast_level);
+  SchemeRainbow(Hct source_color_hct, bool is_dark);
+};
+
+}  // namespace material_color_utilities
+
+#endif  // CPP_SCHEME_SCHEME_RAINBOW_H_

third_party/material_color_utilities/cpp/scheme/scheme_tonal_spot.cc

@@ -0,0 +1,49 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "cpp/scheme/scheme_tonal_spot.h"
+
+#include "cpp/cam/hct.h"
+#include "cpp/dynamiccolor/dynamic_scheme.h"
+#include "cpp/dynamiccolor/variant.h"
+#include "cpp/palettes/tones.h"
+
+namespace material_color_utilities {
+
+SchemeTonalSpot::SchemeTonalSpot(Hct set_source_color_hct, bool set_is_dark,
+                                 double set_contrast_level)
+    : DynamicScheme(
+          /*set_source_color_hct:*/ set_source_color_hct,
+          /*variant:*/ Variant::kTonalSpot,
+          /*contrast_level:*/ set_contrast_level,
+          /*is_dark:*/ set_is_dark,
+          /*primary_palette:*/
+          TonalPalette(set_source_color_hct.get_hue(), 36.0),
+          /*secondary_palette:*/
+          TonalPalette(set_source_color_hct.get_hue(), 16.0),
+          /*tertiary_palette:*/
+          TonalPalette(
+              SanitizeDegreesDouble(set_source_color_hct.get_hue() + 60), 24.0),
+          /*neutral_palette:*/
+          TonalPalette(set_source_color_hct.get_hue(), 6.0),
+          /*neutral_variant_palette:*/
+          TonalPalette(set_source_color_hct.get_hue(), 8.0)) {}
+
+SchemeTonalSpot::SchemeTonalSpot(Hct set_source_color_hct, bool set_is_dark)
+    : SchemeTonalSpot::SchemeTonalSpot(set_source_color_hct, set_is_dark, 0.0) {
+}
+
+}  // namespace material_color_utilities

third_party/material_color_utilities/cpp/scheme/scheme_tonal_spot.h

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CPP_SCHEME_SCHEME_TONAL_SPOT_H_
+#define CPP_SCHEME_SCHEME_TONAL_SPOT_H_
+
+#include "cpp/cam/hct.h"
+#include "cpp/dynamiccolor/dynamic_scheme.h"
+
+namespace material_color_utilities {
+
+struct SchemeTonalSpot : public DynamicScheme {
+  SchemeTonalSpot(Hct source_color_hct, bool is_dark, double contrast_level);
+  SchemeTonalSpot(Hct source_color_hct, bool is_dark);
+};
+
+}  // namespace material_color_utilities
+
+#endif  // CPP_SCHEME_SCHEME_TONAL_SPOT_H_

third_party/material_color_utilities/cpp/scheme/scheme_vibrant.cc

@@ -0,0 +1,61 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "cpp/scheme/scheme_vibrant.h"
+
+#include <vector>
+
+#include "cpp/cam/hct.h"
+#include "cpp/dynamiccolor/dynamic_scheme.h"
+#include "cpp/dynamiccolor/variant.h"
+#include "cpp/palettes/tones.h"
+
+namespace material_color_utilities {
+
+const std::vector<double> kHues = {0, 41, 61, 101, 131, 181, 251, 301, 360};
+
+const std::vector<double> kSecondaryRotations = {18, 15, 10, 12, 15,
+                                                 18, 15, 12, 12};
+
+const std::vector<double> kTertiaryRotations = {35, 30, 20, 25, 30,
+                                                35, 30, 25, 25};
+
+SchemeVibrant::SchemeVibrant(Hct set_source_color_hct, bool set_is_dark,
+                             double set_contrast_level)
+    : DynamicScheme(
+          /*set_source_color_hct:*/ set_source_color_hct,
+          /*variant:*/ Variant::kVibrant,
+          /*contrast_level:*/ set_contrast_level,
+          /*is_dark:*/ set_is_dark,
+          /*primary_palette:*/
+          TonalPalette(set_source_color_hct.get_hue(), 200.0),
+          /*secondary_palette:*/
+          TonalPalette(DynamicScheme::GetRotatedHue(set_source_color_hct, kHues,
+                                                    kSecondaryRotations),
+                       24.0),
+          /*tertiary_palette:*/
+          TonalPalette(DynamicScheme::GetRotatedHue(set_source_color_hct, kHues,
+                                                    kTertiaryRotations),
+                       32.0),
+          /*neutral_palette:*/
+          TonalPalette(set_source_color_hct.get_hue(), 10.0),
+          /*neutral_variant_palette:*/
+          TonalPalette(set_source_color_hct.get_hue(), 12.0)) {}
+
+SchemeVibrant::SchemeVibrant(Hct set_source_color_hct, bool set_is_dark)
+    : SchemeVibrant::SchemeVibrant(set_source_color_hct, set_is_dark, 0.0) {}
+
+}  // namespace material_color_utilities

third_party/material_color_utilities/cpp/scheme/scheme_vibrant.h

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2023 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CPP_SCHEME_SCHEME_VARIANT_H_
+#define CPP_SCHEME_SCHEME_VARIANT_H_
+
+#include "cpp/cam/hct.h"
+#include "cpp/dynamiccolor/dynamic_scheme.h"
+
+namespace material_color_utilities {
+
+struct SchemeVibrant : public DynamicScheme {
+  SchemeVibrant(Hct source_color_hct, bool is_dark, double contrast_level);
+  SchemeVibrant(Hct source_color_hct, bool is_dark);
+};
+
+}  // namespace material_color_utilities
+
+#endif  // CPP_SCHEME_SCHEME_VARIANT_H_

third_party/material_color_utilities/cpp/score/score.cc

@@ -0,0 +1,124 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "cpp/score/score.h"
+
+#include <algorithm>
+#include <cmath>
+#include <cstdint>
+#include <map>
+#include <utility>
+#include <vector>
+
+#include "cpp/cam/hct.h"
+#include "cpp/utils/utils.h"
+
+namespace material_color_utilities {
+
+constexpr double kTargetChroma = 48.0;  // A1 Chroma
+constexpr double kWeightProportion = 0.7;
+constexpr double kWeightChromaAbove = 0.3;
+constexpr double kWeightChromaBelow = 0.1;
+constexpr double kCutoffChroma = 5.0;
+constexpr double kCutoffExcitedProportion = 0.01;
+
+bool CompareScoredHCT(const std::pair<Hct, double>& a,
+                      const std::pair<Hct, double>& b) {
+  return a.second > b.second;
+}
+
+std::vector<Argb> RankedSuggestions(
+    const std::map<Argb, uint32_t>& argb_to_population,
+    const ScoreOptions& options) {
+  // Get the HCT color for each Argb value, while finding the per hue count and
+  // total count.
+  std::vector<Hct> colors_hct;
+  std::vector<uint32_t> hue_population(360, 0);
+  double population_sum = 0;
+  for (const auto& [argb, population] : argb_to_population) {
+    Hct hct(argb);
+    colors_hct.push_back(hct);
+    int hue = floor(hct.get_hue());
+    hue_population[hue] += population;
+    population_sum += population;
+  }
+
+  // Hues with more usage in neighboring 30 degree slice get a larger number.
+  std::vector<double> hue_excited_proportions(360, 0.0);
+  for (int hue = 0; hue < 360; hue++) {
+    double proportion = hue_population[hue] / population_sum;
+    for (int i = hue - 14; i < hue + 16; i++) {
+      int neighbor_hue = SanitizeDegreesInt(i);
+      hue_excited_proportions[neighbor_hue] += proportion;
+    }
+  }
+
+  // Scores each HCT color based on usage and chroma, while optionally
+  // filtering out values that do not have enough chroma or usage.
+  std::vector<std::pair<Hct, double>> scored_hcts;
+  for (Hct hct : colors_hct) {
+    int hue = SanitizeDegreesInt(round(hct.get_hue()));
+    double proportion = hue_excited_proportions[hue];
+    if (options.filter && (hct.get_chroma() < kCutoffChroma ||
+                           proportion <= kCutoffExcitedProportion)) {
+      continue;
+    }
+
+    double proportion_score = proportion * 100.0 * kWeightProportion;
+    double chroma_weight = hct.get_chroma() < kTargetChroma
+                               ? kWeightChromaBelow
+                               : kWeightChromaAbove;
+    double chroma_score = (hct.get_chroma() - kTargetChroma) * chroma_weight;
+    double score = proportion_score + chroma_score;
+    scored_hcts.push_back({hct, score});
+  }
+  // Sorted so that colors with higher scores come first.
+  sort(scored_hcts.begin(), scored_hcts.end(), CompareScoredHCT);
+
+  // Iterates through potential hue differences in degrees in order to select
+  // the colors with the largest distribution of hues possible. Starting at
+  // 90 degrees(maximum difference for 4 colors) then decreasing down to a
+  // 15 degree minimum.
+  std::vector<Hct> chosen_colors;
+  for (int difference_degrees = 90; difference_degrees >= 15;
+       difference_degrees--) {
+    chosen_colors.clear();
+    for (auto entry : scored_hcts) {
+      Hct hct = entry.first;
+      auto duplicate_hue = std::find_if(
+          chosen_colors.begin(), chosen_colors.end(),
+          [&hct, difference_degrees](Hct chosen_hct) {
+            return DiffDegrees(hct.get_hue(), chosen_hct.get_hue()) <
+                   difference_degrees;
+          });
+      if (duplicate_hue == chosen_colors.end()) {
+        chosen_colors.push_back(hct);
+        if (chosen_colors.size() >= options.desired) break;
+      }
+    }
+    if (chosen_colors.size() >= options.desired) break;
+  }
+  std::vector<Argb> colors;
+  if (chosen_colors.empty()) {
+    colors.push_back(options.fallback_color_argb);
+  }
+  for (auto chosen_hct : chosen_colors) {
+    colors.push_back(chosen_hct.ToInt());
+  }
+  return colors;
+}
+
+}  // namespace material_color_utilities

third_party/material_color_utilities/cpp/score/score.h

@@ -0,0 +1,59 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CPP_SCORE_SCORE_H_
+#define CPP_SCORE_SCORE_H_
+
+#include <cstdlib>
+#include <map>
+#include <vector>
+
+#include "cpp/utils/utils.h"
+
+namespace material_color_utilities {
+
+/**
+ * Default options for ranking colors based on usage counts.
+ * `desired`: is the max count of the colors returned.
+ * `fallback_color_argb`: Is the default color that should be used if no
+ *                        other colors are suitable.
+ * `filter`: controls if the resulting colors should be filtered to not include
+ *         hues that are not used often enough, and colors that are effectively
+ *         grayscale.
+ */
+struct ScoreOptions {
+  size_t desired = 4;  // 4 colors matches the Android wallpaper picker.
+  int fallback_color_argb = 0xff4285f4;  // Google Blue.
+  bool filter = true;                    // Avoid unsuitable colors.
+};
+
+/**
+ * Given a map with keys of colors and values of how often the color appears,
+ * rank the colors based on suitability for being used for a UI theme.
+ *
+ * The list returned is of length <= [desired]. The recommended color is the
+ * first item, the least suitable is the last. There will always be at least
+ * one color returned. If all the input colors were not suitable for a theme,
+ * a default fallback color will be provided, Google Blue, or supplied fallback
+ * color. The default number of colors returned is 4, simply because that's the
+ * # of colors display in Android 12's wallpaper picker.
+ */
+std::vector<Argb> RankedSuggestions(
+    const std::map<Argb, uint32_t>& argb_to_population,
+    const ScoreOptions& options = {});
+}  // namespace material_color_utilities
+
+#endif  // CPP_SCORE_SCORE_H_

third_party/material_color_utilities/cpp/temperature/temperature_cache.cc

@@ -0,0 +1,250 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "cpp/temperature/temperature_cache.h"
+
+#include <algorithm>
+#include <cmath>
+#include <map>
+#include <vector>
+
+#include "cpp/cam/hct.h"
+#include "cpp/quantize/lab.h"
+#include "cpp/utils/utils.h"
+
+namespace material_color_utilities {
+
+TemperatureCache::TemperatureCache(Hct input) : input_(input) {}
+
+Hct TemperatureCache::GetComplement() {
+  if (precomputed_complement_.has_value()) {
+    return precomputed_complement_.value();
+  }
+
+  double coldest_hue = GetColdest().get_hue();
+  double coldest_temp = GetTempsByHct().at(GetColdest());
+
+  double warmest_hue = GetWarmest().get_hue();
+  double warmest_temp = GetTempsByHct().at(GetWarmest());
+  double range = warmest_temp - coldest_temp;
+  bool start_hue_is_coldest_to_warmest =
+      IsBetween(input_.get_hue(), coldest_hue, warmest_hue);
+  double start_hue =
+      start_hue_is_coldest_to_warmest ? warmest_hue : coldest_hue;
+  double end_hue = start_hue_is_coldest_to_warmest ? coldest_hue : warmest_hue;
+  double direction_of_rotation = 1.0;
+  double smallest_error = 1000.0;
+  Hct answer = GetHctsByHue().at((int)round(input_.get_hue()));
+
+  double complement_relative_temp = (1.0 - GetRelativeTemperature(input_));
+  // Find the color in the other section, closest to the inverse percentile
+  // of the input color. This is the complement.
+  for (double hue_addend = 0.0; hue_addend <= 360.0; hue_addend += 1.0) {
+    double hue =
+        SanitizeDegreesDouble(start_hue + direction_of_rotation * hue_addend);
+    if (!IsBetween(hue, start_hue, end_hue)) {
+      continue;
+    }
+    Hct possible_answer = GetHctsByHue().at((int)round(hue));
+    double relative_temp =
+        (GetTempsByHct().at(possible_answer) - coldest_temp) / range;
+    double error = std::abs(complement_relative_temp - relative_temp);
+    if (error < smallest_error) {
+      smallest_error = error;
+      answer = possible_answer;
+    }
+  }
+  precomputed_complement_ = answer;
+  return precomputed_complement_.value();
+}
+
+std::vector<Hct> TemperatureCache::GetAnalogousColors() {
+  return GetAnalogousColors(5, 12);
+}
+
+std::vector<Hct> TemperatureCache::GetAnalogousColors(int count,
+                                                      int divisions) {
+  // The starting hue is the hue of the input color.
+  int start_hue = (int)round(input_.get_hue());
+  Hct start_hct = GetHctsByHue().at(start_hue);
+  double last_temp = GetRelativeTemperature(start_hct);
+
+  std::vector<Hct> all_colors;
+  all_colors.push_back(start_hct);
+
+  double absolute_total_temp_delta = 0.0;
+  for (int i = 0; i < 360; i++) {
+    int hue = SanitizeDegreesInt(start_hue + i);
+    Hct hct = GetHctsByHue().at(hue);
+    double temp = GetRelativeTemperature(hct);
+    double temp_delta = std::abs(temp - last_temp);
+    last_temp = temp;
+    absolute_total_temp_delta += temp_delta;
+  }
+
+  int hue_addend = 1;
+  double temp_step = absolute_total_temp_delta / (double)divisions;
+  double total_temp_delta = 0.0;
+  last_temp = GetRelativeTemperature(start_hct);
+  while (all_colors.size() < static_cast<size_t>(divisions)) {
+    int hue = SanitizeDegreesInt(start_hue + hue_addend);
+    Hct hct = GetHctsByHue().at(hue);
+    double temp = GetRelativeTemperature(hct);
+    double temp_delta = std::abs(temp - last_temp);
+    total_temp_delta += temp_delta;
+
+    double desired_total_temp_delta_for_index = (all_colors.size() * temp_step);
+    bool index_satisfied =
+        total_temp_delta >= desired_total_temp_delta_for_index;
+    int index_addend = 1;
+    // Keep adding this hue to the answers until its temperature is
+    // insufficient. This ensures consistent behavior when there aren't
+    // `divisions` discrete steps between 0 and 360 in hue with `temp_step`
+    // delta in temperature between them.
+    //
+    // For example, white and black have no analogues: there are no other
+    // colors at T100/T0. Therefore, they should just be added to the array
+    // as answers.
+    while (index_satisfied &&
+           all_colors.size() < static_cast<size_t>(divisions)) {
+      all_colors.push_back(hct);
+      desired_total_temp_delta_for_index =
+          ((all_colors.size() + index_addend) * temp_step);
+      index_satisfied = total_temp_delta >= desired_total_temp_delta_for_index;
+      index_addend++;
+    }
+    last_temp = temp;
+    hue_addend++;
+
+    if (hue_addend > 360) {
+      while (all_colors.size() < static_cast<size_t>(divisions)) {
+        all_colors.push_back(hct);
+      }
+      break;
+    }
+  }
+
+  std::vector<Hct> answers;
+  answers.push_back(input_);
+
+  int ccw_count = (int)floor(((double)count - 1.0) / 2.0);
+  for (int i = 1; i < (ccw_count + 1); i++) {
+    int index = 0 - i;
+    while (index < 0) {
+      index = all_colors.size() + index;
+    }
+    if (static_cast<size_t>(index) >= all_colors.size()) {
+      index = index % all_colors.size();
+    }
+    answers.insert(answers.begin(), all_colors.at(index));
+  }
+
+  int cw_count = count - ccw_count - 1;
+  for (int i = 1; i < (cw_count + 1); i++) {
+    size_t index = i;
+    while (index < 0) {
+      index = all_colors.size() + index;
+    }
+    if (index >= all_colors.size()) {
+      index = index % all_colors.size();
+    }
+    answers.push_back(all_colors.at(index));
+  }
+
+  return answers;
+}
+
+double TemperatureCache::GetRelativeTemperature(Hct hct) {
+  double range =
+      GetTempsByHct().at(GetWarmest()) - GetTempsByHct().at(GetColdest());
+  double difference_from_coldest =
+      GetTempsByHct().at(hct) - GetTempsByHct().at(GetColdest());
+  // Handle when there's no difference in temperature between warmest and
+  // coldest: for example, at T100, only one color is available, white.
+  if (range == 0.) {
+    return 0.5;
+  }
+  return difference_from_coldest / range;
+}
+
+double TemperatureCache::RawTemperature(Hct color) {
+  Lab lab = LabFromInt(color.ToInt());
+  double hue = SanitizeDegreesDouble(atan2(lab.b, lab.a) * 180.0 / kPi);
+  double chroma = hypot(lab.a, lab.b);
+  return -0.5 + 0.02 * pow(chroma, 1.07) *
+                    cos(SanitizeDegreesDouble(hue - 50.) * kPi / 180);
+}
+
+Hct TemperatureCache::GetColdest() { return GetHctsByTemp().at(0); }
+
+std::vector<Hct> TemperatureCache::GetHctsByHue() {
+  if (precomputed_hcts_by_hue_.has_value()) {
+    return precomputed_hcts_by_hue_.value();
+  }
+  std::vector<Hct> hcts;
+  for (double hue = 0.; hue <= 360.; hue += 1.) {
+    Hct color_at_hue(hue, input_.get_chroma(), input_.get_tone());
+    hcts.push_back(color_at_hue);
+  }
+  precomputed_hcts_by_hue_ = hcts;
+  return precomputed_hcts_by_hue_.value();
+}
+
+std::vector<Hct> TemperatureCache::GetHctsByTemp() {
+  if (precomputed_hcts_by_temp_.has_value()) {
+    return precomputed_hcts_by_temp_.value();
+  }
+
+  std::vector<Hct> hcts(GetHctsByHue());
+  hcts.push_back(input_);
+  std::map<Hct, double> temps_by_hct(GetTempsByHct());
+  sort(hcts.begin(), hcts.end(),
+       [temps_by_hct](const Hct a, const Hct b) -> bool {
+         return temps_by_hct.at(a) < temps_by_hct.at(b);
+       });
+  precomputed_hcts_by_temp_ = hcts;
+  return precomputed_hcts_by_temp_.value();
+}
+
+std::map<Hct, double> TemperatureCache::GetTempsByHct() {
+  if (precomputed_temps_by_hct_.has_value()) {
+    return precomputed_temps_by_hct_.value();
+  }
+
+  std::vector<Hct> all_hcts(GetHctsByHue());
+  all_hcts.push_back(input_);
+
+  std::map<Hct, double> temperatures_by_hct;
+  for (Hct hct : all_hcts) {
+    temperatures_by_hct[hct] = RawTemperature(hct);
+  }
+
+  precomputed_temps_by_hct_ = temperatures_by_hct;
+  return precomputed_temps_by_hct_.value();
+}
+
+Hct TemperatureCache::GetWarmest() {
+  return GetHctsByTemp().at(GetHctsByTemp().size() - 1);
+}
+
+bool TemperatureCache::IsBetween(double angle, double a, double b) {
+  if (a < b) {
+    return a <= angle && angle <= b;
+  }
+  return a <= angle || angle <= b;
+}
+
+}  // namespace material_color_utilities

third_party/material_color_utilities/cpp/temperature/temperature_cache.h

@@ -0,0 +1,140 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CPP_TEMPERATURE_TEMPERATURE_CACHE_H_
+#define CPP_TEMPERATURE_TEMPERATURE_CACHE_H_
+
+#include <map>
+#include <optional>
+#include <vector>
+
+#include "cpp/cam/hct.h"
+
+namespace material_color_utilities {
+
+/**
+ * Design utilities using color temperature theory.
+ *
+ * <p>Analogous colors, complementary color, and cache to efficiently, lazily,
+ * generate data for calculations when needed.
+ */
+class TemperatureCache {
+ public:
+  /**
+   * Create a cache that allows calculation of ex. complementary and analogous
+   * colors.
+   *
+   * @param input Color to find complement/analogous colors of. Any colors will
+   * have the same tone, and chroma as the input color, modulo any restrictions
+   * due to the other hues having lower limits on chroma.
+   */
+  explicit TemperatureCache(Hct input);
+
+  /**
+   * A color that complements the input color aesthetically.
+   *
+   * <p>In art, this is usually described as being across the color wheel.
+   * History of this shows intent as a color that is just as cool-warm as the
+   * input color is warm-cool.
+   */
+  Hct GetComplement();
+
+  /**
+   * 5 colors that pair well with the input color.
+   *
+   * <p>The colors are equidistant in temperature and adjacent in hue.
+   */
+  std::vector<Hct> GetAnalogousColors();
+
+  /**
+   * A set of colors with differing hues, equidistant in temperature.
+   *
+   * <p>In art, this is usually described as a set of 5 colors on a color wheel
+   * divided into 12 sections. This method allows provision of either of those
+   * values.
+   *
+   * <p>Behavior is undefined when count or divisions is 0. When divisions <
+   * count, colors repeat.
+   *
+   * @param count The number of colors to return, includes the input color.
+   * @param divisions The number of divisions on the color wheel.
+   */
+  std::vector<Hct> GetAnalogousColors(int count, int divisions);
+
+  /**
+   * Temperature relative to all colors with the same chroma and tone.
+   *
+   * @param hct HCT to find the relative temperature of.
+   * @return Value on a scale from 0 to 1.
+   */
+  double GetRelativeTemperature(Hct hct);
+
+  /**
+   * Value representing cool-warm factor of a color. Values below 0 are
+   * considered cool, above, warm.
+   *
+   * <p>Color science has researched emotion and harmony, which art uses to
+   * select colors. Warm-cool is the foundation of analogous and complementary
+   * colors. See: - Li-Chen Ou's Chapter 19 in Handbook of Color Psychology
+   * (2015). - Josef Albers' Interaction of Color chapters 19 and 21.
+   *
+   * <p>Implementation of Ou, Woodcock and Wright's algorithm, which uses
+   * Lab/LCH color space. Return value has these properties:<br>
+   * - Values below 0 are cool, above 0 are warm.<br>
+   * - Lower bound: -9.66. Chroma is infinite. Assuming max of Lab chroma
+   * 130.<br>
+   * - Upper bound: 8.61. Chroma is infinite. Assuming max of Lab chroma 130.
+   */
+  static double RawTemperature(Hct color);
+
+ private:
+  Hct input_;
+
+  std::optional<Hct> precomputed_complement_;
+  std::optional<std::vector<Hct>> precomputed_hcts_by_temp_;
+  std::optional<std::vector<Hct>> precomputed_hcts_by_hue_;
+  std::optional<std::map<Hct, double>> precomputed_temps_by_hct_;
+
+  /** Coldest color with same chroma and tone as input. */
+  Hct GetColdest();
+
+  /** Warmest color with same chroma and tone as input. */
+  Hct GetWarmest();
+
+  /** Determines if an angle is between two other angles, rotating clockwise. */
+  static bool IsBetween(double angle, double a, double b);
+
+  /**
+   * HCTs for all colors with the same chroma/tone as the input.
+   *
+   * <p>Sorted by hue, ex. index 0 is hue 0.
+   */
+  std::vector<Hct> GetHctsByHue();
+
+  /**
+   * HCTs for all colors with the same chroma/tone as the input.
+   *
+   * <p>Sorted from coldest first to warmest last.
+   */
+  std::vector<Hct> GetHctsByTemp();
+
+  /** Keys of HCTs in GetHctsByTemp, values of raw temperature. */
+  std::map<Hct, double> GetTempsByHct();
+};
+
+}  // namespace material_color_utilities
+
+#endif  // CPP_TEMPERATURE_TEMPERATURE_CACHE_H_

third_party/material_color_utilities/cpp/utils/utils.cc

@@ -0,0 +1,181 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "cpp/utils/utils.h"
+
+#include <math.h>
+
+#include <algorithm>
+#include <cmath>
+#include <cstdint>
+#include <cstdio>
+#include <sstream>
+#include <iomanip>
+#include <string>
+
+namespace material_color_utilities {
+
+int RedFromInt(const Argb argb) { return (argb & 0x00ff0000) >> 16; }
+
+int GreenFromInt(const Argb argb) { return (argb & 0x0000ff00) >> 8; }
+
+int BlueFromInt(const Argb argb) { return (argb & 0x000000ff); }
+
+Argb ArgbFromRgb(const int red, const int green, const int blue) {
+  return 0xFF000000 | ((red & 0xff) << 16) | ((green & 0xff) << 8) |
+         (blue & 0xff);
+}
+
+// Converts a color from linear RGB components to ARGB format.
+Argb ArgbFromLinrgb(Vec3 linrgb) {
+  int r = Delinearized(linrgb.a);
+  int g = Delinearized(linrgb.b);
+  int b = Delinearized(linrgb.c);
+
+  return 0xFF000000 | ((r & 0x0ff) << 16) | ((g & 0x0ff) << 8) | (b & 0x0ff);
+}
+
+int Delinearized(const double rgb_component) {
+  double normalized = rgb_component / 100;
+  double delinearized;
+  if (normalized <= 0.0031308) {
+    delinearized = normalized * 12.92;
+  } else {
+    delinearized = 1.055 * std::pow(normalized, 1.0 / 2.4) - 0.055;
+  }
+  return std::clamp((int)round(delinearized * 255.0), 0, 255);
+}
+
+double Linearized(const int rgb_component) {
+  double normalized = rgb_component / 255.0;
+  if (normalized <= 0.040449936) {
+    return normalized / 12.92 * 100.0;
+  } else {
+    return std::pow((normalized + 0.055) / 1.055, 2.4) * 100.0;
+  }
+}
+
+int AlphaFromInt(Argb argb) { return (argb & 0xff000000) >> 24; }
+
+bool IsOpaque(Argb argb) { return AlphaFromInt(argb) == 255; }
+
+double LstarFromArgb(Argb argb) {
+  // xyz from argb
+  int red = (argb & 0x00ff0000) >> 16;
+  int green = (argb & 0x0000ff00) >> 8;
+  int blue = (argb & 0x000000ff);
+  double red_l = Linearized(red);
+  double green_l = Linearized(green);
+  double blue_l = Linearized(blue);
+  double y = 0.2126 * red_l + 0.7152 * green_l + 0.0722 * blue_l;
+  return LstarFromY(y);
+}
+
+double YFromLstar(double lstar) {
+  static const double ke = 8.0;
+  if (lstar > ke) {
+    double cube_root = (lstar + 16.0) / 116.0;
+    double cube = cube_root * cube_root * cube_root;
+    return cube * 100.0;
+  } else {
+    return lstar / (24389.0 / 27.0) * 100.0;
+  }
+}
+
+double LstarFromY(double y) {
+  static const double e = 216.0 / 24389.0;
+  double yNormalized = y / 100.0;
+  if (yNormalized <= e) {
+    return (24389.0 / 27.0) * yNormalized;
+  } else {
+    return 116.0 * std::pow(yNormalized, 1.0 / 3.0) - 16.0;
+  }
+}
+
+int SanitizeDegreesInt(const int degrees) {
+  if (degrees < 0) {
+    return (degrees % 360) + 360;
+  } else if (degrees >= 360.0) {
+    return degrees % 360;
+  } else {
+    return degrees;
+  }
+}
+
+// Sanitizes a degree measure as a floating-point number.
+//
+// Returns a degree measure between 0.0 (inclusive) and 360.0 (exclusive).
+double SanitizeDegreesDouble(const double degrees) {
+  if (degrees < 0.0) {
+    return fmod(degrees, 360.0) + 360;
+  } else if (degrees >= 360.0) {
+    return fmod(degrees, 360.0);
+  } else {
+    return degrees;
+  }
+}
+
+double DiffDegrees(const double a, const double b) {
+  return 180.0 - abs(abs(a - b) - 180.0);
+}
+
+double RotationDirection(const double from, const double to) {
+  double increasing_difference = SanitizeDegreesDouble(to - from);
+  return increasing_difference <= 180.0 ? 1.0 : -1.0;
+}
+
+// Converts a color in ARGB format to a hexadecimal string in lowercase.
+//
+// For instance: hex_from_argb(0xff012345) == "ff012345"
+std::string HexFromArgb(Argb argb) {
+  std::ostringstream os;
+  os << std::hex << argb;
+  return os.str();
+}
+
+Argb IntFromLstar(const double lstar) {
+  double y = YFromLstar(lstar);
+  int component = Delinearized(y);
+  return ArgbFromRgb(component, component, component);
+}
+
+// The signum function.
+//
+// Returns 1 if num > 0, -1 if num < 0, and 0 if num = 0
+int Signum(double num) {
+  if (num < 0) {
+    return -1;
+  } else if (num == 0) {
+    return 0;
+  } else {
+    return 1;
+  }
+}
+
+double Lerp(double start, double stop, double amount) {
+  return (1.0 - amount) * start + amount * stop;
+}
+
+Vec3 MatrixMultiply(Vec3 input, const double matrix[3][3]) {
+  double a =
+      input.a * matrix[0][0] + input.b * matrix[0][1] + input.c * matrix[0][2];
+  double b =
+      input.a * matrix[1][0] + input.b * matrix[1][1] + input.c * matrix[1][2];
+  double c =
+      input.a * matrix[2][0] + input.b * matrix[2][1] + input.c * matrix[2][2];
+  return (Vec3){a, b, c};
+}
+}  // namespace material_color_utilities

third_party/material_color_utilities/cpp/utils/utils.h

@@ -0,0 +1,211 @@
+/*
+ * Copyright 2022 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef CPP_UTILS_UTILS_H_
+#define CPP_UTILS_UTILS_H_
+
+#include <cstdint>
+#include <string>
+
+namespace material_color_utilities {
+
+using Argb = uint32_t;
+
+/**
+ * A vector with three floating-point numbers as components.
+ */
+struct Vec3 {
+  double a = 0.0;
+  double b = 0.0;
+  double c = 0.0;
+};
+
+/**
+ * Value of pi.
+ */
+inline constexpr double kPi = 3.141592653589793;
+
+/**
+ * Returns the standard white point; white on a sunny day.
+ */
+inline constexpr double kWhitePointD65[] = {95.047, 100.0, 108.883};
+
+/**
+ * Returns the red component of a color in ARGB format.
+ */
+int RedFromInt(const Argb argb);
+
+/**
+ * Returns the green component of a color in ARGB format.
+ */
+int GreenFromInt(const Argb argb);
+
+/**
+ * Returns the blue component of a color in ARGB format.
+ */
+int BlueFromInt(const Argb argb);
+
+/**
+ * Returns the alpha component of a color in ARGB format.
+ */
+int AlphaFromInt(const Argb argb);
+
+/**
+ * Converts a color from RGB components to ARGB format.
+ */
+Argb ArgbFromRgb(const int red, const int green, const int blue);
+
+/**
+ * Converts a color from linear RGB components to ARGB format.
+ */
+Argb ArgbFromLinrgb(Vec3 linrgb);
+
+/**
+ * Returns whether a color in ARGB format is opaque.
+ */
+bool IsOpaque(const Argb argb);
+
+/**
+ * Sanitizes a degree measure as an integer.
+ *
+ * @return a degree measure between 0 (inclusive) and 360 (exclusive).
+ */
+int SanitizeDegreesInt(const int degrees);
+
+/**
+ * Sanitizes a degree measure as an floating-point number.
+ *
+ * @return a degree measure between 0.0 (inclusive) and 360.0 (exclusive).
+ */
+double SanitizeDegreesDouble(const double degrees);
+
+/**
+ * Distance of two points on a circle, represented using degrees.
+ */
+double DiffDegrees(const double a, const double b);
+
+/**
+ * Sign of direction change needed to travel from one angle to
+ * another.
+ *
+ * For angles that are 180 degrees apart from each other, both
+ * directions have the same travel distance, so either direction is
+ * shortest. The value 1.0 is returned in this case.
+ *
+ * @param from The angle travel starts from, in degrees.
+ *
+ * @param to The angle travel ends at, in degrees.
+ *
+ * @return -1 if decreasing from leads to the shortest travel
+ * distance, 1 if increasing from leads to the shortest travel
+ * distance.
+ */
+double RotationDirection(const double from, const double to);
+
+/**
+ * Computes the L* value of a color in ARGB representation.
+ *
+ * @param argb ARGB representation of a color
+ *
+ * @return L*, from L*a*b*, coordinate of the color
+ */
+double LstarFromArgb(const Argb argb);
+
+/**
+ * Returns the hexadecimal representation of a color.
+ */
+std::string HexFromArgb(Argb argb);
+
+/**
+ * Linearizes an RGB component.
+ *
+ * @param rgb_component 0 <= rgb_component <= 255, represents R/G/B
+ * channel
+ *
+ * @return 0.0 <= output <= 100.0, color channel converted to
+ * linear RGB space
+ */
+double Linearized(const int rgb_component);
+
+/**
+ * Delinearizes an RGB component.
+ *
+ * @param rgb_component 0.0 <= rgb_component <= 100.0, represents linear
+ * R/G/B channel
+ *
+ * @return 0 <= output <= 255, color channel converted to regular
+ * RGB space
+ */
+int Delinearized(const double rgb_component);
+
+/**
+ * Converts an L* value to a Y value.
+ *
+ * L* in L*a*b* and Y in XYZ measure the same quantity, luminance.
+ *
+ * L* measures perceptual luminance, a linear scale. Y in XYZ
+ * measures relative luminance, a logarithmic scale.
+ *
+ * @param lstar L* in L*a*b*. 0.0 <= L* <= 100.0
+ *
+ * @return Y in XYZ. 0.0 <= Y <= 100.0
+ */
+double YFromLstar(const double lstar);
+
+/**
+ * Converts a Y value to an L* value.
+ *
+ * L* in L*a*b* and Y in XYZ measure the same quantity, luminance.
+ *
+ * L* measures perceptual luminance, a linear scale. Y in XYZ
+ * measures relative luminance, a logarithmic scale.
+ *
+ * @param y Y in XYZ. 0.0 <= Y <= 100.0
+ *
+ * @return L* in L*a*b*. 0.0 <= L* <= 100.0
+ */
+double LstarFromY(const double y);
+
+/**
+ * Converts an L* value to an ARGB representation.
+ *
+ * @param lstar L* in L*a*b*. 0.0 <= L* <= 100.0
+ *
+ * @return ARGB representation of grayscale color with lightness matching L*
+ */
+Argb IntFromLstar(const double lstar);
+
+/**
+ * The signum function.
+ *
+ * @return 1 if num > 0, -1 if num < 0, and 0 if num = 0
+ */
+int Signum(double num);
+
+/**
+ * The linear interpolation function.
+ *
+ * @return start if amount = 0 and stop if amount = 1
+ */
+double Lerp(double start, double stop, double amount);
+
+/**
+ * Multiplies a 1x3 row vector with a 3x3 matrix, returning the product.
+ */
+Vec3 MatrixMultiply(Vec3 input, const double matrix[3][3]);
+
+}  // namespace material_color_utilities
+#endif  // CPP_UTILS_UTILS_H_

tools/palette-generator-analysis.py

@@ -0,0 +1,285 @@
+#!/usr/bin/env python3
+"""
+Analyze Noctalia's C++ palette generator against Python + matugen references.
+
+Usage:
+    ./tools/palette-generator-analysis.py <wallpaper>
+    ./tools/palette-generator-analysis.py <wallpaper> --fail-threshold 20
+
+Three backends:
+  - Noctalia  : ../build-debug/noctalia theme <img> --scheme <s> --dark
+  - Python    : the upstream reference in noctalia-shell/Scripts/python
+  - Matugen   : Rust reference (M3 schemes only)
+
+Exit code: 0 if all diffs are under --fail-threshold (default: unlimited),
+           1 on failure or threshold exceeded.
+"""
+
+import argparse
+import json
+import subprocess
+import sys
+from pathlib import Path
+
+SCRIPT_DIR = Path(__file__).parent.resolve()
+REPO_DIR = SCRIPT_DIR.parent
+NOCTALIA_BIN = REPO_DIR / "build-debug" / "noctalia"
+
+# Absolute path into the upstream Python reference.
+PYTHON_THEMING_DIR = Path.home() / "Development/misc/noctalia/noctalia-shell/Scripts/python/src/theming"
+PYTHON_PROCESSOR = PYTHON_THEMING_DIR / "template-processor.py"
+
+# Pull in Python's Hct for hue/chroma classification.
+sys.path.insert(0, str(PYTHON_THEMING_DIR))
+try:
+    from lib.color import Color  # noqa: E402
+    from lib.hct import Hct  # noqa: E402
+except ImportError:
+    Color = None
+    Hct = None
+
+M3_SCHEMES = ["m3-tonal-spot", "m3-fruit-salad", "m3-rainbow", "m3-content", "m3-monochrome"]
+CUSTOM_SCHEMES = ["vibrant", "faithful", "dysfunctional", "muted"]
+
+
+def python_scheme_name(scheme: str) -> str:
+    """Translate our m3-* names to what the upstream Python processor expects."""
+    return scheme[3:] if scheme.startswith("m3-") else scheme
+
+
+def matugen_scheme_name(scheme: str) -> str:
+    return scheme[3:] if scheme.startswith("m3-") else scheme
+KEY_TOKENS = ["primary", "secondary", "tertiary", "surface", "on_surface",
+              "primary_container", "surface_container", "outline"]
+
+
+def hex_to_rgb(h: str) -> tuple[int, int, int]:
+    h = h.lstrip('#')
+    return int(h[0:2], 16), int(h[2:4], 16), int(h[4:6], 16)
+
+
+def rgb_distance(a: str, b: str) -> float:
+    r1, g1, b1 = hex_to_rgb(a)
+    r2, g2, b2 = hex_to_rgb(b)
+    return ((r1 - r2) ** 2 + (g1 - g2) ** 2 + (b1 - b2) ** 2) ** 0.5
+
+
+def max_lsb(a: str, b: str) -> int:
+    r1, g1, b1 = hex_to_rgb(a)
+    r2, g2, b2 = hex_to_rgb(b)
+    return max(abs(r1 - r2), abs(g1 - g2), abs(b1 - b2))
+
+
+def hue_diff(h1: float, h2: float) -> float:
+    d = abs(h1 - h2)
+    return min(d, 360.0 - d)
+
+
+def get_hct(hex_color: str):
+    if Color is None:
+        return None
+    return Color.from_hex(hex_color).to_hct()
+
+
+def run_python(image: Path, scheme: str) -> dict | None:
+    try:
+        out = subprocess.run(
+            [sys.executable, str(PYTHON_PROCESSOR), str(image),
+             "--scheme-type", python_scheme_name(scheme), "--dark"],
+            capture_output=True, text=True, check=True,
+        )
+        data = json.loads(out.stdout)
+        return data.get("dark", data)
+    except Exception as e:
+        print(f"  python {scheme}: {e}", file=sys.stderr)
+        return None
+
+
+def run_matugen(image: Path, scheme: str) -> dict | None:
+    try:
+        out = subprocess.run(
+            ["matugen", "image", str(image), "--json", "hex",
+             "--dry-run", "-m", "dark",
+             "--source-color-index", "0",
+             "--old-json-output",
+             "-t", f"scheme-{matugen_scheme_name(scheme)}"],
+            capture_output=True, text=True, check=True,
+        )
+        data = json.loads(out.stdout)
+        colors = data.get("colors", {})
+        # Each entry is {"dark": "#hex", "default": "#hex", "light": "#hex"}.
+        return {k: v.get("dark", v) for k, v in colors.items() if isinstance(v, dict)}
+    except Exception as e:
+        print(f"  matugen {scheme}: {e}", file=sys.stderr)
+        return None
+
+
+def run_noctalia(image: Path, scheme: str) -> dict | None:
+    try:
+        out = subprocess.run(
+            [str(NOCTALIA_BIN), "theme", str(image),
+             "--scheme", scheme, "--dark"],
+            capture_output=True, text=True, check=True,
+        )
+        return json.loads(out.stdout)
+    except Exception as e:
+        print(f"  noctalia {scheme}: {e}", file=sys.stderr)
+        return None
+
+
+def quality_bucket(our: str, ref: str) -> tuple[str, str]:
+    """Return (metric_str, bucket) using hue for high-chroma, RGB for low."""
+    try:
+        h1 = get_hct(our)
+        h2 = get_hct(ref)
+        avg = (h1.chroma + h2.chroma) / 2
+    except Exception:
+        avg = 0
+
+    if avg < 15:
+        d = rgb_distance(our, ref)
+        bucket = "excellent" if d < 10 else "good" if d < 25 else "fair" if d < 50 else "poor"
+        return f"{d:5.1f} rgb", bucket
+    else:
+        d = hue_diff(h1.hue, h2.hue)
+        bucket = "excellent" if d < 5 else "good" if d < 15 else "fair" if d < 30 else "poor"
+        return f"{d:5.1f} hue", bucket
+
+
+def compare_m3(image: Path, scheme: str, has_matugen: bool) -> list[int]:
+    """Return list of LSB diffs vs the best available reference."""
+    print(f"\n─── {scheme} ───")
+    py = run_python(image, scheme)
+    noct = run_noctalia(image, scheme)
+    mat = run_matugen(image, scheme) if has_matugen else None
+
+    if not py or not noct:
+        print("  ! missing reference output, skipping")
+        return []
+
+    hdr = f"  {'Token':<26} {'Python':<10} {'Matugen':<10} {'Noctalia':<10} {'Δ Py↔Noct':<14} {'Δ Mat↔Noct':<14}"
+    print(hdr)
+    print("  " + "─" * (len(hdr) - 2))
+
+    diffs: list[int] = []
+    for token in KEY_TOKENS:
+        pv = py.get(token, "")
+        nv = noct.get(token, "")
+        mv = (mat or {}).get(token, "")
+        if not (pv and nv):
+            continue
+
+        py_noct_metric, py_noct_bucket = quality_bucket(nv, pv)
+        if mv:
+            mat_noct_metric, mat_noct_bucket = quality_bucket(nv, mv)
+            mat_col = f"{mat_noct_metric} {mat_noct_bucket[:4]}"
+        else:
+            mat_col = "-"
+
+        lsb = max_lsb(pv, nv)
+        diffs.append(lsb)
+
+        print(f"  {token:<26} {pv:<10} {mv or '-':<10} {nv:<10} "
+              f"{py_noct_metric} {py_noct_bucket[:4]:<5} {mat_col:<14}  "
+              f"(Δ{lsb})")
+    return diffs
+
+
+def compare_custom(image: Path, scheme: str) -> list[int]:
+    print(f"\n─── {scheme} ───")
+    py = run_python(image, scheme)
+    noct = run_noctalia(image, scheme)
+    if not py or not noct:
+        print("  ! missing reference output, skipping")
+        return []
+
+    hdr = f"  {'Token':<26} {'Python':<10} {'Noctalia':<10} {'Δ Py↔Noct':<14}"
+    print(hdr)
+    print("  " + "─" * (len(hdr) - 2))
+
+    diffs: list[int] = []
+    for token in KEY_TOKENS:
+        pv = py.get(token, "")
+        nv = noct.get(token, "")
+        if not (pv and nv):
+            continue
+        metric, bucket = quality_bucket(nv, pv)
+        lsb = max_lsb(pv, nv)
+        diffs.append(lsb)
+        print(f"  {token:<26} {pv:<10} {nv:<10} "
+              f"{metric} {bucket[:4]:<5}  (Δ{lsb})")
+    return diffs
+
+
+def main() -> int:
+    parser = argparse.ArgumentParser(
+        description="Compare Noctalia C++ palette generator vs Python/matugen"
+    )
+    parser.add_argument("wallpaper", type=Path)
+    parser.add_argument("--fail-threshold", type=int, default=-1,
+                        help="Exit 1 if any token's max-channel LSB diff exceeds N")
+    parser.add_argument("--no-matugen", action="store_true")
+    parser.add_argument("--schemes", nargs="+",
+                        help="Limit to a subset of schemes")
+    args = parser.parse_args()
+
+    if not args.wallpaper.exists():
+        print(f"error: not found: {args.wallpaper}", file=sys.stderr)
+        return 1
+    if not NOCTALIA_BIN.exists():
+        print(f"error: noctalia not built: {NOCTALIA_BIN}", file=sys.stderr)
+        return 1
+
+    has_matugen = False
+    if not args.no_matugen:
+        try:
+            subprocess.run(["matugen", "--version"], capture_output=True, check=True)
+            has_matugen = True
+        except Exception:
+            print("note: matugen not available, skipping its column")
+
+    print(f"\nWallpaper: {args.wallpaper.name}")
+    print("=" * 78)
+    print("M3 SCHEMES (Python is a MCU port; Matugen is the Rust reference)")
+    print("=" * 78)
+
+    all_diffs: list[tuple[str, int]] = []
+
+    m3 = M3_SCHEMES if not args.schemes else [s for s in M3_SCHEMES if s in args.schemes]
+    for s in m3:
+        for d in compare_m3(args.wallpaper, s, has_matugen):
+            all_diffs.append((s, d))
+
+    print()
+    print("=" * 78)
+    print("CUSTOM SCHEMES (Python is the only reference)")
+    print("=" * 78)
+
+    custom = CUSTOM_SCHEMES if not args.schemes else [s for s in CUSTOM_SCHEMES if s in args.schemes]
+    for s in custom:
+        for d in compare_custom(args.wallpaper, s):
+            all_diffs.append((s, d))
+
+    print()
+    print("─" * 78)
+    print("Summary")
+    per_scheme: dict[str, list[int]] = {}
+    for s, d in all_diffs:
+        per_scheme.setdefault(s, []).append(d)
+    for s in list(per_scheme):
+        ds = per_scheme[s]
+        if ds:
+            print(f"  {s:<14} max Δ={max(ds):>3}  mean Δ={sum(ds)/len(ds):>5.1f}  ({len(ds)} tokens)")
+
+    if args.fail_threshold >= 0:
+        worst = max((d for _, d in all_diffs), default=0)
+        if worst > args.fail_threshold:
+            print(f"\nFAIL: worst Δ={worst} > threshold {args.fail_threshold}")
+            return 1
+        print(f"\nOK: worst Δ={worst} ≤ threshold {args.fail_threshold}")
+
+    return 0
+
+
+if __name__ == "__main__":
+    sys.exit(main())