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
12class SkBitmap;
13
14namespace color_utils {
15
16// Represents an HSL color.
17struct HSL {
18  double h;
19  double s;
20  double l;
21};
22
23GFX_EXPORT unsigned char GetLuminanceForColor(SkColor color);
24
25// Calculated according to http://www.w3.org/TR/WCAG20/#relativeluminancedef
26GFX_EXPORT double RelativeLuminance(SkColor color);
27
28// Note: these transformations assume sRGB as the source color space
29GFX_EXPORT void SkColorToHSL(SkColor c, HSL* hsl);
30GFX_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.
42GFX_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).
60GFX_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.
64GFX_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.
70GFX_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|.
76GFX_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).
87GFX_EXPORT SkColor GetReadableColor(SkColor foreground, SkColor background);
88
89// Invert a color.
90GFX_EXPORT SkColor InvertColor(SkColor color);
91
92// Gets a Windows system color as a SkColor
93GFX_EXPORT SkColor GetSysSkColor(int which);
94
95}  // namespace color_utils
96
97#endif  // UI_GFX_COLOR_UTILS_H_
98