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 // Validates an |hsl| value passed in from an untrusted source.
  33 //
  34 // If we were starting from scratch, we'd throw some sort of exception to the
  35 // user here, but there's already code out there that acts as if -1 == 0 and
  36 // 1 == 2, so just Clamp the values to [0, 1] instead.
  37 GFX_EXPORT void ClampHSL(HSL* hsl);
  38
  39 // Determines whether the given |hsl| falls within the given range for each
  40 // component. All components of |hsl| are expected to be in the range [0, 1].
  41 //
  42 // If a component is negative in either |lower_bound| or |upper_bound|, that
  43 // component will be ignored.
  44 //
  45 // For hue, the lower bound should be in the range [0, 1] and the upper bound
  46 // should be in the range [(lower bound), (lower bound + 1)].
  47 // For saturation and value, bounds should be specified in the range [0, 1],
  48 // with the lower bound less than the upper bound.
  49 GFX_EXPORT bool IsWithinHSLRange(const HSL& hsl,
  50                                  const HSL& lower_bound,
  51                                  const HSL& upper_bound);
  52
  53 // HSL-Shift an SkColor. The shift values are in the range of 0-1, with the
  54 // option to specify -1 for 'no change'. The shift values are defined as:
  55 // hsl_shift[0] (hue): The absolute hue value - 0 and 1 map
  56 //    to 0 and 360 on the hue color wheel (red).
  57 // hsl_shift[1] (saturation): A saturation shift, with the
  58 //    following key values:
  59 //    0 = remove all color.
  60 //    0.5 = leave unchanged.
  61 //    1 = fully saturate the image.
  62 // hsl_shift[2] (lightness): A lightness shift, with the
  63 //    following key values:
  64 //    0 = remove all lightness (make all pixels black).
  65 //    0.5 = leave unchanged.
  66 //    1 = full lightness (make all pixels white).
  67 GFX_EXPORT SkColor HSLShift(SkColor color, const HSL& shift);
  68
  69 // Builds a histogram based on the Y' of the Y'UV representation of
  70 // this image.
  71 GFX_EXPORT void BuildLumaHistogram(const SkBitmap& bitmap, int histogram[256]);
  72
  73 // Returns a blend of the supplied colors, ranging from |background| (for
  74 // |alpha| == 0) to |foreground| (for |alpha| == 255). The alpha channels of
  75 // the supplied colors are also taken into account, so the returned color may
  76 // be partially transparent.
  77 GFX_EXPORT SkColor AlphaBlend(SkColor foreground, SkColor background,
  78                               SkAlpha alpha);
  79
  80 // Makes a dark color lighter or a light color darker by blending |color| with
  81 // white or black depending on its current luminance.  |alpha| controls the
  82 // amount of white or black that will be alpha-blended into |color|.
  83 GFX_EXPORT SkColor BlendTowardOppositeLuminance(SkColor color, SkAlpha alpha);
  84
  85 // Given an opaque foreground and background color, try to return a foreground
  86 // color that is "readable" over the background color by luma-inverting the
  87 // foreground color and then picking whichever foreground color has higher
  88 // contrast against the background color.  You should not pass colors with
  89 // non-255 alpha to this routine, since determining the correct behavior in such
  90 // cases can be impossible.
  91 //
  92 // NOTE: This won't do anything but waste time if the supplied foreground color
  93 // has a luma value close to the midpoint (0.5 in the HSL representation).
  94 GFX_EXPORT SkColor GetReadableColor(SkColor foreground, SkColor background);
  95
  96 // Invert a color.
  97 GFX_EXPORT SkColor InvertColor(SkColor color);
  98
  99 // Gets a Windows system color as a SkColor
 100 GFX_EXPORT SkColor GetSysSkColor(int which);
 101
 102 }  // namespace color_utils
 103
 104 #endif  // UI_GFX_COLOR_UTILS_H_