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 // Determines whether the given |hsl| falls within the given range for each
  33 // component. All components of |hsl| are expected to be in the range [0, 1].
  34 //
  35 // If a component is negative in either |lower_bound| or |upper_bound|, that
  36 // component will be ignored.
  37 //
  38 // For hue, the lower bound should be in the range [0, 1] and the upper bound
  39 // should be in the range [(lower bound), (lower bound + 1)].
  40 // For saturation and value, bounds should be specified in the range [0, 1],
  41 // with the lower bound less than the upper bound.
  42 GFX_EXPORT bool IsWithinHSLRange(const HSL& hsl,
  43                                  const HSL& lower_bound,
  44                                  const HSL& upper_bound);
  45
  46 // HSL-Shift an SkColor. The shift values are in the range of 0-1, with the
  47 // option to specify -1 for 'no change'. The shift values are defined as:
  48 // hsl_shift[0] (hue): The absolute hue value - 0 and 1 map
  49 //    to 0 and 360 on the hue color wheel (red).
  50 // hsl_shift[1] (saturation): A saturation shift, with the
  51 //    following key values:
  52 //    0 = remove all color.
  53 //    0.5 = leave unchanged.
  54 //    1 = fully saturate the image.
  55 // hsl_shift[2] (lightness): A lightness shift, with the
  56 //    following key values:
  57 //    0 = remove all lightness (make all pixels black).
  58 //    0.5 = leave unchanged.
  59 //    1 = full lightness (make all pixels white).
  60 GFX_EXPORT SkColor HSLShift(SkColor color, const HSL& shift);
  61
  62 // Builds a histogram based on the Y' of the Y'UV representation of
  63 // this image.
  64 GFX_EXPORT void BuildLumaHistogram(const SkBitmap& bitmap, int histogram[256]);
  65
  66 // Returns a blend of the supplied colors, ranging from |background| (for
  67 // |alpha| == 0) to |foreground| (for |alpha| == 255). The alpha channels of
  68 // the supplied colors are also taken into account, so the returned color may
  69 // be partially transparent.
  70 GFX_EXPORT SkColor AlphaBlend(SkColor foreground, SkColor background,
  71                               SkAlpha alpha);
  72
  73 // Makes a dark color lighter or a light color darker by blending |color| with
  74 // white or black depending on its current luminance.  |alpha| controls the
  75 // amount of white or black that will be alpha-blended into |color|.
  76 GFX_EXPORT SkColor BlendTowardOppositeLuminance(SkColor color, SkAlpha alpha);
  77
  78 // Given an opaque foreground and background color, try to return a foreground
  79 // color that is "readable" over the background color by luma-inverting the
  80 // foreground color and then picking whichever foreground color has higher
  81 // contrast against the background color.  You should not pass colors with
  82 // non-255 alpha to this routine, since determining the correct behavior in such
  83 // cases can be impossible.
  84 //
  85 // NOTE: This won't do anything but waste time if the supplied foreground color
  86 // has a luma value close to the midpoint (0.5 in the HSL representation).
  87 GFX_EXPORT SkColor GetReadableColor(SkColor foreground, SkColor background);
  88
  89 // Invert a color.
  90 GFX_EXPORT SkColor InvertColor(SkColor color);
  91
  92 // Gets a Windows system color as a SkColor
  93 GFX_EXPORT SkColor GetSysSkColor(int which);
  94
  95 }  // namespace color_utils
  96
  97 #endif  // UI_GFX_COLOR_UTILS_H_