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 // Helper functions -----------------------------------------------------------
  25
  26 namespace {
  27
  28 int calcHue(double temp1, double temp2, double hue) {
  29   if (hue < 0.0)
  30     ++hue;
  31   else if (hue > 1.0)
  32     --hue;
  33
  34   double result = temp1;
  35   if (hue * 6.0 < 1.0)
  36     result = temp1 + (temp2 - temp1) * hue * 6.0;
  37   else if (hue * 2.0 < 1.0)
  38     result = temp2;
  39   else if (hue * 3.0 < 2.0)
  40     result = temp1 + (temp2 - temp1) * (2.0 / 3.0 - hue) * 6.0;
  41
  42   // Scale the result from 0 - 255 and round off the value.
  43   return static_cast<int>(result * 255 + .5);
  44 }
  45
  46 // Next two functions' formulas from:
  47 // http://www.w3.org/TR/WCAG20/#relativeluminancedef
  48 // http://www.w3.org/TR/WCAG20/#contrast-ratiodef
  49
  50 double ConvertSRGB(double eight_bit_component) {
  51   const double component = eight_bit_component / 255.0;
  52   return (component <= 0.03928) ?
  53       (component / 12.92) : pow((component + 0.055) / 1.055, 2.4);
  54 }
  55
  56 SkColor LumaInvertColor(SkColor color) {
  57   HSL hsl;
  58   SkColorToHSL(color, &hsl);
  59   hsl.l = 1.0 - hsl.l;
  60   return HSLToSkColor(hsl, 255);
  61 }
  62
  63 double ContrastRatio(double foreground_luminance, double background_luminance) {
  64   // NOTE: Only pass in numbers obtained from RelativeLuminance(), since those
  65   // are guaranteed to be > 0 and thus not cause a divide-by-zero error here.
  66   return (foreground_luminance > background_luminance) ?
  67       (foreground_luminance / background_luminance) :
  68       (background_luminance / foreground_luminance);
  69 }
  70
  71 }  // namespace
  72
  73 // ----------------------------------------------------------------------------
  74
  75 unsigned char GetLuminanceForColor(SkColor color) {
  76   int luma = static_cast<int>((0.3 * SkColorGetR(color)) +
  77                               (0.59 * SkColorGetG(color)) +
  78                               (0.11 * SkColorGetB(color)));
  79   return std::max(std::min(luma, 255), 0);
  80 }
  81
  82 double RelativeLuminance(SkColor color) {
  83   return (0.2126 * ConvertSRGB(SkColorGetR(color))) +
  84       (0.7152 * ConvertSRGB(SkColorGetG(color))) +
  85       (0.0722 * ConvertSRGB(SkColorGetB(color))) + 0.05;
  86 }
  87
  88 void SkColorToHSL(SkColor c, HSL* hsl) {
  89   double r = static_cast<double>(SkColorGetR(c)) / 255.0;
  90   double g = static_cast<double>(SkColorGetG(c)) / 255.0;
  91   double b = static_cast<double>(SkColorGetB(c)) / 255.0;
  92   double vmax = std::max(std::max(r, g), b);
  93   double vmin = std::min(std::min(r, g), b);
  94   double delta = vmax - vmin;
  95   hsl->l = (vmax + vmin) / 2;
  96   if (SkColorGetR(c) == SkColorGetG(c) && SkColorGetR(c) == SkColorGetB(c)) {
  97     hsl->h = hsl->s = 0;
  98   } else {
  99     double dr = (((vmax - r) / 6.0) + (delta / 2.0)) / delta;
 100     double dg = (((vmax - g) / 6.0) + (delta / 2.0)) / delta;
 101     double db = (((vmax - b) / 6.0) + (delta / 2.0)) / delta;
 102     // We need to compare for the max value because comparing vmax to r,
 103     // g or b can sometimes result in values overflowing registers.
 104     if (r >= g && r >= b)
 105       hsl->h = db - dg;
 106     else if (g >= r && g >= b)
 107       hsl->h = (1.0 / 3.0) + dr - db;
 108     else  // (b >= r && b >= g)
 109       hsl->h = (2.0 / 3.0) + dg - dr;
 110
 111     if (hsl->h < 0.0)
 112       ++hsl->h;
 113     else if (hsl->h > 1.0)
 114       --hsl->h;
 115
 116     hsl->s = delta / ((hsl->l < 0.5) ? (vmax + vmin) : (2 - vmax - vmin));
 117   }
 118 }
 119
 120 SkColor HSLToSkColor(const HSL& hsl, SkAlpha alpha) {
 121   double hue = hsl.h;
 122   double saturation = hsl.s;
 123   double lightness = hsl.l;
 124
 125   // If there's no color, we don't care about hue and can do everything based
 126   // on brightness.
 127   if (!saturation) {
 128     uint8 light;
 129
 130     if (lightness < 0)
 131       light = 0;
 132     else if (lightness >= 1.0)
 133       light = 255;
 134     else
 135       light = SkDoubleToFixed(lightness) >> 8;
 136
 137     return SkColorSetARGB(alpha, light, light, light);
 138   }
 139
 140   double temp2 = (lightness < 0.5) ?
 141       (lightness * (1.0 + saturation)) :
 142       (lightness + saturation - (lightness * saturation));
 143   double temp1 = 2.0 * lightness - temp2;
 144   return SkColorSetARGB(alpha,
 145       calcHue(temp1, temp2, hue + 1.0 / 3.0),
 146       calcHue(temp1, temp2, hue),
 147       calcHue(temp1, temp2, hue - 1.0 / 3.0));
 148 }
 149
 150 SkColor HSLShift(SkColor color, const HSL& shift) {
 151   HSL hsl;
 152   int alpha = SkColorGetA(color);
 153   SkColorToHSL(color, &hsl);
 154
 155   // Replace the hue with the tint's hue.
 156   if (shift.h >= 0)
 157     hsl.h = shift.h;
 158
 159   // Change the saturation.
 160   if (shift.s >= 0) {
 161     if (shift.s <= 0.5)
 162       hsl.s *= shift.s * 2.0;
 163     else
 164       hsl.s += (1.0 - hsl.s) * ((shift.s - 0.5) * 2.0);
 165   }
 166
 167   SkColor result = HSLToSkColor(hsl, alpha);
 168
 169   if (shift.l < 0)
 170     return result;
 171
 172   // Lightness shifts in the style of popular image editors aren't
 173   // actually represented in HSL - the L value does have some effect
 174   // on saturation.
 175   double r = static_cast<double>(SkColorGetR(result));
 176   double g = static_cast<double>(SkColorGetG(result));
 177   double b = static_cast<double>(SkColorGetB(result));
 178   if (shift.l <= 0.5) {
 179     r *= (shift.l * 2.0);
 180     g *= (shift.l * 2.0);
 181     b *= (shift.l * 2.0);
 182   } else {
 183     r += (255.0 - r) * ((shift.l - 0.5) * 2.0);
 184     g += (255.0 - g) * ((shift.l - 0.5) * 2.0);
 185     b += (255.0 - b) * ((shift.l - 0.5) * 2.0);
 186   }
 187   return SkColorSetARGB(alpha,
 188                         static_cast<int>(r),
 189                         static_cast<int>(g),
 190                         static_cast<int>(b));
 191 }
 192
 193 void BuildLumaHistogram(const SkBitmap& bitmap, int histogram[256]) {
 194   SkAutoLockPixels bitmap_lock(bitmap);
 195   if (!bitmap.getPixels())
 196     return;
 197
 198   // Assume ARGB_8888 format.
 199   DCHECK(bitmap.config() == SkBitmap::kARGB_8888_Config);
 200
 201   int pixel_width = bitmap.width();
 202   int pixel_height = bitmap.height();
 203   for (int y = 0; y < pixel_height; ++y) {
 204     SkColor* current_color = static_cast<uint32_t*>(bitmap.getAddr32(0, y));
 205     for (int x = 0; x < pixel_width; ++x, ++current_color)
 206       histogram[GetLuminanceForColor(*current_color)]++;
 207   }
 208 }
 209
 210 SkColor AlphaBlend(SkColor foreground, SkColor background, SkAlpha alpha) {
 211   if (alpha == 0)
 212     return background;
 213   if (alpha == 255)
 214     return foreground;
 215
 216   int f_alpha = SkColorGetA(foreground);
 217   int b_alpha = SkColorGetA(background);
 218
 219   double normalizer = (f_alpha * alpha + b_alpha * (255 - alpha)) / 255.0;
 220   if (normalizer == 0.0)
 221     return SkColorSetARGB(0, 0, 0, 0);
 222
 223   double f_weight = f_alpha * alpha / normalizer;
 224   double b_weight = b_alpha * (255 - alpha) / normalizer;
 225
 226   double r = (SkColorGetR(foreground) * f_weight +
 227               SkColorGetR(background) * b_weight) / 255.0;
 228   double g = (SkColorGetG(foreground) * f_weight +
 229               SkColorGetG(background) * b_weight) / 255.0;
 230   double b = (SkColorGetB(foreground) * f_weight +
 231               SkColorGetB(background) * b_weight) / 255.0;
 232
 233   return SkColorSetARGB(static_cast<int>(normalizer),
 234                         static_cast<int>(r),
 235                         static_cast<int>(g),
 236                         static_cast<int>(b));
 237 }
 238
 239 SkColor GetReadableColor(SkColor foreground, SkColor background) {
 240   const SkColor foreground2 = LumaInvertColor(foreground);
 241   const double background_luminance = RelativeLuminance(background);
 242   return (ContrastRatio(RelativeLuminance(foreground), background_luminance) >=
 243           ContrastRatio(RelativeLuminance(foreground2), background_luminance)) ?
 244       foreground : foreground2;
 245 }
 246
 247 SkColor InvertColor(SkColor color) {
 248   return SkColorSetARGB(
 249       SkColorGetA(color),
 250       255 - SkColorGetR(color),
 251       255 - SkColorGetG(color),
 252       255 - SkColorGetB(color));
 253 }
 254
 255 SkColor GetSysSkColor(int which) {
 256 #if defined(OS_WIN)
 257   return skia::COLORREFToSkColor(GetSysColor(which));
 258 #else
 259   NOTIMPLEMENTED();
 260   return SK_ColorLTGRAY;
 261 #endif
 262 }
 263
 264 }  // namespace color_utils