ui/gfx/color_utils.cc

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "ui/gfx/color_utils.h"
   6
   7 #include <math.h>
   8 #if defined(OS_WIN)
   9 #include <windows.h>
  10 #endif
  11
  12 #include <algorithm>
  13
  14 #include "base/basictypes.h"
  15 #include "base/logging.h"
  16 #include "build/build_config.h"
  17 #if defined(OS_WIN)
  18 #include "skia/ext/skia_utils_win.h"
  19 #endif
  20 #include "third_party/skia/include/core/SkBitmap.h"
  21
  22 namespace color_utils {
  23
  24
  25 // Helper functions -----------------------------------------------------------
  26
  27 namespace {
  28
  29 int calcHue(double temp1, double temp2, double hue) {
  30   if (hue < 0.0)
  31     ++hue;
  32   else if (hue > 1.0)
  33     --hue;
  34
  35   double result = temp1;
  36   if (hue * 6.0 < 1.0)
  37     result = temp1 + (temp2 - temp1) * hue * 6.0;
  38   else if (hue * 2.0 < 1.0)
  39     result = temp2;
  40   else if (hue * 3.0 < 2.0)
  41     result = temp1 + (temp2 - temp1) * (2.0 / 3.0 - hue) * 6.0;
  42
  43   // Scale the result from 0 - 255 and round off the value.
  44   return static_cast<int>(result * 255 + .5);
  45 }
  46
  47 // Next two functions' formulas from:
  48 // http://www.w3.org/TR/WCAG20/#relativeluminancedef
  49 // http://www.w3.org/TR/WCAG20/#contrast-ratiodef
  50
  51 double ConvertSRGB(double eight_bit_component) {
  52   const double component = eight_bit_component / 255.0;
  53   return (component <= 0.03928) ?
  54       (component / 12.92) : pow((component + 0.055) / 1.055, 2.4);
  55 }
  56
  57 SkColor LumaInvertColor(SkColor color) {
  58   HSL hsl;
  59   SkColorToHSL(color, &hsl);
  60   hsl.l = 1.0 - hsl.l;
  61   return HSLToSkColor(hsl, 255);
  62 }
  63
  64 double ContrastRatio(double foreground_luminance, double background_luminance) {
  65   DCHECK_GE(foreground_luminance, 0.0);
  66   DCHECK_GE(background_luminance, 0.0);
  67   foreground_luminance += 0.05;
  68   background_luminance += 0.05;
  69   return (foreground_luminance > background_luminance) ?
  70       (foreground_luminance / background_luminance) :
  71       (background_luminance / foreground_luminance);
  72 }
  73
  74 }  // namespace
  75
  76
  77 // ----------------------------------------------------------------------------
  78
  79 unsigned char GetLuminanceForColor(SkColor color) {
  80   int luma = static_cast<int>((0.3 * SkColorGetR(color)) +
  81                               (0.59 * SkColorGetG(color)) +
  82                               (0.11 * SkColorGetB(color)));
  83   return std::max(std::min(luma, 255), 0);
  84 }
  85
  86 double RelativeLuminance(SkColor color) {
  87   return (0.2126 * ConvertSRGB(SkColorGetR(color))) +
  88          (0.7152 * ConvertSRGB(SkColorGetG(color))) +
  89          (0.0722 * ConvertSRGB(SkColorGetB(color)));
  90 }
  91
  92 void SkColorToHSL(SkColor c, HSL* hsl) {
  93   double r = static_cast<double>(SkColorGetR(c)) / 255.0;
  94   double g = static_cast<double>(SkColorGetG(c)) / 255.0;
  95   double b = static_cast<double>(SkColorGetB(c)) / 255.0;
  96   double vmax = std::max(std::max(r, g), b);
  97   double vmin = std::min(std::min(r, g), b);
  98   double delta = vmax - vmin;
  99   hsl->l = (vmax + vmin) / 2;
 100   if (SkColorGetR(c) == SkColorGetG(c) && SkColorGetR(c) == SkColorGetB(c)) {
 101     hsl->h = hsl->s = 0;
 102   } else {
 103     double dr = (((vmax - r) / 6.0) + (delta / 2.0)) / delta;
 104     double dg = (((vmax - g) / 6.0) + (delta / 2.0)) / delta;
 105     double db = (((vmax - b) / 6.0) + (delta / 2.0)) / delta;
 106     // We need to compare for the max value because comparing vmax to r, g, or b
 107     // can sometimes result in values overflowing registers.
 108     if (r >= g && r >= b)
 109       hsl->h = db - dg;
 110     else if (g >= r && g >= b)
 111       hsl->h = (1.0 / 3.0) + dr - db;
 112     else  // (b >= r && b >= g)
 113       hsl->h = (2.0 / 3.0) + dg - dr;
 114
 115     if (hsl->h < 0.0)
 116       ++hsl->h;
 117     else if (hsl->h > 1.0)
 118       --hsl->h;
 119
 120     hsl->s = delta / ((hsl->l < 0.5) ? (vmax + vmin) : (2 - vmax - vmin));
 121   }
 122 }
 123
 124 SkColor HSLToSkColor(const HSL& hsl, SkAlpha alpha) {
 125   double hue = hsl.h;
 126   double saturation = hsl.s;
 127   double lightness = hsl.l;
 128
 129   // If there's no color, we don't care about hue and can do everything based on
 130   // brightness.
 131   if (!saturation) {
 132     uint8 light;
 133
 134     if (lightness < 0)
 135       light = 0;
 136     else if (lightness >= 1.0)
 137       light = 255;
 138     else
 139       light = SkDoubleToFixed(lightness) >> 8;
 140
 141     return SkColorSetARGB(alpha, light, light, light);
 142   }
 143
 144   double temp2 = (lightness < 0.5) ?
 145       (lightness * (1.0 + saturation)) :
 146       (lightness + saturation - (lightness * saturation));
 147   double temp1 = 2.0 * lightness - temp2;
 148   return SkColorSetARGB(alpha,
 149       calcHue(temp1, temp2, hue + 1.0 / 3.0),
 150       calcHue(temp1, temp2, hue),
 151       calcHue(temp1, temp2, hue - 1.0 / 3.0));
 152 }
 153
 154 SkColor HSLShift(SkColor color, const HSL& shift) {
 155   HSL hsl;
 156   int alpha = SkColorGetA(color);
 157   SkColorToHSL(color, &hsl);
 158
 159   // Replace the hue with the tint's hue.
 160   if (shift.h >= 0)
 161     hsl.h = shift.h;
 162
 163   // Change the saturation.
 164   if (shift.s >= 0) {
 165     if (shift.s <= 0.5)
 166       hsl.s *= shift.s * 2.0;
 167     else
 168       hsl.s += (1.0 - hsl.s) * ((shift.s - 0.5) * 2.0);
 169   }
 170
 171   SkColor result = HSLToSkColor(hsl, alpha);
 172
 173   if (shift.l < 0)
 174     return result;
 175
 176   // Lightness shifts in the style of popular image editors aren't actually
 177   // represented in HSL - the L value does have some effect on saturation.
 178   double r = static_cast<double>(SkColorGetR(result));
 179   double g = static_cast<double>(SkColorGetG(result));
 180   double b = static_cast<double>(SkColorGetB(result));
 181   if (shift.l <= 0.5) {
 182     r *= (shift.l * 2.0);
 183     g *= (shift.l * 2.0);
 184     b *= (shift.l * 2.0);
 185   } else {
 186     r += (255.0 - r) * ((shift.l - 0.5) * 2.0);
 187     g += (255.0 - g) * ((shift.l - 0.5) * 2.0);
 188     b += (255.0 - b) * ((shift.l - 0.5) * 2.0);
 189   }
 190   return SkColorSetARGB(alpha,
 191                         static_cast<int>(r),
 192                         static_cast<int>(g),
 193                         static_cast<int>(b));
 194 }
 195
 196 void BuildLumaHistogram(const SkBitmap& bitmap, int histogram[256]) {
 197   DCHECK_EQ(SkBitmap::kARGB_8888_Config, bitmap.config());
 198
 199   SkAutoLockPixels bitmap_lock(bitmap);
 200
 201   int pixel_width = bitmap.width();
 202   int pixel_height = bitmap.height();
 203   for (int y = 0; y < pixel_height; ++y) {
 204     for (int x = 0; x < pixel_width; ++x)
 205       ++histogram[GetLuminanceForColor(bitmap.getColor(x, y))];
 206   }
 207 }
 208
 209 SkColor AlphaBlend(SkColor foreground, SkColor background, SkAlpha alpha) {
 210   if (alpha == 0)
 211     return background;
 212   if (alpha == 255)
 213     return foreground;
 214
 215   int f_alpha = SkColorGetA(foreground);
 216   int b_alpha = SkColorGetA(background);
 217
 218   double normalizer = (f_alpha * alpha + b_alpha * (255 - alpha)) / 255.0;
 219   if (normalizer == 0.0)
 220     return SK_ColorTRANSPARENT;
 221
 222   double f_weight = f_alpha * alpha / normalizer;
 223   double b_weight = b_alpha * (255 - alpha) / normalizer;
 224
 225   double r = (SkColorGetR(foreground) * f_weight +
 226               SkColorGetR(background) * b_weight) / 255.0;
 227   double g = (SkColorGetG(foreground) * f_weight +
 228               SkColorGetG(background) * b_weight) / 255.0;
 229   double b = (SkColorGetB(foreground) * f_weight +
 230               SkColorGetB(background) * b_weight) / 255.0;
 231
 232   return SkColorSetARGB(static_cast<int>(normalizer),
 233                         static_cast<int>(r),
 234                         static_cast<int>(g),
 235                         static_cast<int>(b));
 236 }
 237
 238 SkColor BlendTowardOppositeLuminance(SkColor color, SkAlpha alpha) {
 239   unsigned char background_luminance =
 240       color_utils::GetLuminanceForColor(color);
 241   const SkColor blend_color =
 242       (background_luminance < 128) ? SK_ColorWHITE : SK_ColorBLACK;
 243   return color_utils::AlphaBlend(blend_color, color, alpha);
 244 }
 245
 246 SkColor GetReadableColor(SkColor foreground, SkColor background) {
 247   const SkColor foreground2 = LumaInvertColor(foreground);
 248   const double background_luminance = RelativeLuminance(background);
 249   return (ContrastRatio(RelativeLuminance(foreground), background_luminance) >=
 250           ContrastRatio(RelativeLuminance(foreground2), background_luminance)) ?
 251       foreground : foreground2;
 252 }
 253
 254 SkColor InvertColor(SkColor color) {
 255   return SkColorSetARGB(
 256       SkColorGetA(color),
 257       255 - SkColorGetR(color),
 258       255 - SkColorGetG(color),
 259       255 - SkColorGetB(color));
 260 }
 261
 262 SkColor GetSysSkColor(int which) {
 263 #if defined(OS_WIN)
 264   return skia::COLORREFToSkColor(GetSysColor(which));
 265 #else
 266   NOTIMPLEMENTED();
 267   return SK_ColorLTGRAY;
 268 #endif
 269 }
 270
 271 }  // namespace color_utils