ui/gfx/color_utils.h

   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 #ifndef UI_GFX_COLOR_UTILS_H_
   6 #define UI_GFX_COLOR_UTILS_H_
   7
   8 #include "base/basictypes.h"
   9 #include "third_party/skia/include/core/SkColor.h"
  10 #include "ui/gfx/gfx_export.h"
  11
  12 class SkBitmap;
  13
  14 namespace color_utils {
  15
  16 // Represents an HSL color.
  17 struct HSL {
  18   double h;
  19   double s;
  20   double l;
  21 };
  22
  23 GFX_EXPORT unsigned char GetLuminanceForColor(SkColor color);
  24
  25 // Calculated according to http://www.w3.org/TR/WCAG20/#relativeluminancedef
  26 GFX_EXPORT double RelativeLuminance(SkColor color);
  27
  28 // Note: these transformations assume sRGB as the source color space
  29 GFX_EXPORT void SkColorToHSL(SkColor c, HSL* hsl);
  30 GFX_EXPORT SkColor HSLToSkColor(const HSL& hsl, SkAlpha alpha);
  31
  32 // HSL-Shift an SkColor. The shift values are in the range of 0-1, with the
  33 // option to specify -1 for 'no change'. The shift values are defined as:
  34 // hsl_shift[0] (hue): The absolute hue value - 0 and 1 map
  35 //    to 0 and 360 on the hue color wheel (red).
  36 // hsl_shift[1] (saturation): A saturation shift, with the
  37 //    following key values:
  38 //    0 = remove all color.
  39 //    0.5 = leave unchanged.
  40 //    1 = fully saturate the image.
  41 // hsl_shift[2] (lightness): A lightness shift, with the
  42 //    following key values:
  43 //    0 = remove all lightness (make all pixels black).
  44 //    0.5 = leave unchanged.
  45 //    1 = full lightness (make all pixels white).
  46 GFX_EXPORT SkColor HSLShift(SkColor color, const HSL& shift);
  47
  48 // Builds a histogram based on the Y' of the Y'UV representation of
  49 // this image.
  50 GFX_EXPORT void BuildLumaHistogram(const SkBitmap& bitmap, int histogram[256]);
  51
  52 // Returns a blend of the supplied colors, ranging from |background| (for
  53 // |alpha| == 0) to |foreground| (for |alpha| == 255). The alpha channels of
  54 // the supplied colors are also taken into account, so the returned color may
  55 // be partially transparent.
  56 GFX_EXPORT SkColor AlphaBlend(SkColor foreground, SkColor background,
  57                               SkAlpha alpha);
  58
  59 // Makes a dark color lighter or a light color darker by blending |color| with
  60 // white or black depending on its current luminance.  |alpha| controls the
  61 // amount of white or black that will be alpha-blended into |color|.
  62 GFX_EXPORT SkColor BlendTowardOppositeLuminance(SkColor color, SkAlpha alpha);
  63
  64 // Given an opaque foreground and background color, try to return a foreground
  65 // color that is "readable" over the background color by luma-inverting the
  66 // foreground color and then picking whichever foreground color has higher
  67 // contrast against the background color.  You should not pass colors with
  68 // non-255 alpha to this routine, since determining the correct behavior in such
  69 // cases can be impossible.
  70 //
  71 // NOTE: This won't do anything but waste time if the supplied foreground color
  72 // has a luma value close to the midpoint (0.5 in the HSL representation).
  73 GFX_EXPORT SkColor GetReadableColor(SkColor foreground, SkColor background);
  74
  75 // Invert a color.
  76 GFX_EXPORT SkColor InvertColor(SkColor color);
  77
  78 // Gets a Windows system color as a SkColor
  79 GFX_EXPORT SkColor GetSysSkColor(int which);
  80
  81 }  // namespace color_utils
  82
  83 #endif  // UI_GFX_COLOR_UTILS_H_