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 <string> 9 #include <tuple> 10 11 #include "base/optional.h" 12 #include "third_party/skia/include/core/SkColor.h" 13 #include "ui/gfx/gfx_export.h" 14 15 class SkBitmap; 16 17 namespace color_utils { 18 19 // Represents an HSL color. 20 struct HSL { 21 double h; 22 double s; 23 double l; 24 }; 25 26 // The blend alpha and resulting color when blending to achieve a desired 27 // contrast raio. 28 struct BlendResult { 29 SkAlpha alpha; 30 SkColor color; 31 }; 32 33 // The minimum contrast between text and background that is still readable. 34 // This value is taken from w3c accessibility guidelines. 35 constexpr float kMinimumReadableContrastRatio = 4.5f; 36 37 // Determines the contrast ratio of two colors or two relative luminance values 38 // (as computed by RelativeLuminance()), calculated according to 39 // http://www.w3.org/TR/WCAG20/#contrast-ratiodef . 40 GFX_EXPORT float GetContrastRatio(SkColor color_a, SkColor color_b); 41 GFX_EXPORT float GetContrastRatio(float luminance_a, float luminance_b); 42 43 // The relative luminance of |color|, that is, the weighted sum of the 44 // linearized RGB components, normalized to 0..1, per BT.709. See 45 // http://www.w3.org/TR/WCAG20/#relativeluminancedef . 46 GFX_EXPORT float GetRelativeLuminance(SkColor color); 47 48 // The luma of |color|, that is, the weighted sum of the gamma-compressed R'G'B' 49 // components, per BT.601, a.k.a. the Y' in Y'UV. See 50 // https://en.wikipedia.org/wiki/Luma_(video). 51 GFX_EXPORT uint8_t GetLuma(SkColor color); 52 53 // Note: these transformations assume sRGB as the source color space 54 GFX_EXPORT void SkColorToHSL(SkColor c, HSL* hsl); 55 GFX_EXPORT SkColor HSLToSkColor(const HSL& hsl, SkAlpha alpha); 56 57 // Determines whether the given |hsl| falls within the given range for each 58 // component. All components of |hsl| are expected to be in the range [0, 1]. 59 // 60 // If a component is negative in either |lower_bound| or |upper_bound|, that 61 // component will be ignored. 62 // 63 // For hue, the lower bound should be in the range [0, 1] and the upper bound 64 // should be in the range [(lower bound), (lower bound + 1)]. 65 // For saturation and value, bounds should be specified in the range [0, 1], 66 // with the lower bound less than the upper bound. 67 GFX_EXPORT bool IsWithinHSLRange(const HSL& hsl, 68 const HSL& lower_bound, 69 const HSL& upper_bound); 70 71 // Makes |hsl| valid input for HSLShift(). Sets values of hue, saturation 72 // and lightness which are outside of the valid range [0, 1] to -1. -1 is a 73 // special value which indicates 'no change'. 74 GFX_EXPORT void MakeHSLShiftValid(HSL* hsl); 75 76 // Returns whether pasing |hsl| to HSLShift() would have any effect. Assumes 77 // |hsl| is a valid shift (as defined by MakeHSLShiftValid()). 78 GFX_EXPORT bool IsHSLShiftMeaningful(const HSL& hsl); 79 80 // HSL-Shift an SkColor. The shift values are in the range of 0-1, with the 81 // option to specify -1 for 'no change'. The shift values are defined as: 82 // hsl_shift[0] (hue): The absolute hue value - 0 and 1 map 83 // to 0 and 360 on the hue color wheel (red). 84 // hsl_shift[1] (saturation): A saturation shift, with the 85 // following key values: 86 // 0 = remove all color. 87 // 0.5 = leave unchanged. 88 // 1 = fully saturate the image. 89 // hsl_shift[2] (lightness): A lightness shift, with the 90 // following key values: 91 // 0 = remove all lightness (make all pixels black). 92 // 0.5 = leave unchanged. 93 // 1 = full lightness (make all pixels white). 94 GFX_EXPORT SkColor HSLShift(SkColor color, const HSL& shift); 95 96 // Builds a histogram based on the Y' of the Y'UV representation of this image. 97 GFX_EXPORT void BuildLumaHistogram(const SkBitmap& bitmap, int histogram[256]); 98 99 // Calculates how "boring" an image is. The boring score is the 100 // 0,1 ranged percentage of pixels that are the most common 101 // luma. Higher boring scores indicate that a higher percentage of a 102 // bitmap are all the same brightness. 103 GFX_EXPORT double CalculateBoringScore(const SkBitmap& bitmap); 104 105 // Returns a blend of the supplied colors, ranging from |background| (for 106 // |alpha| == 0) to |foreground| (for |alpha| == 255). The alpha channels of 107 // the supplied colors are also taken into account, so the returned color may 108 // be partially transparent. 109 GFX_EXPORT SkColor AlphaBlend(SkColor foreground, 110 SkColor background, 111 SkAlpha alpha); 112 113 // As above, but with alpha specified as 0..1. 114 GFX_EXPORT SkColor AlphaBlend(SkColor foreground, 115 SkColor background, 116 float alpha); 117 118 // Returns the color that results from painting |foreground| on top of 119 // |background|. 120 GFX_EXPORT SkColor GetResultingPaintColor(SkColor foreground, 121 SkColor background); 122 123 // Returns true if |color| contrasts more with white than the darkest color. 124 GFX_EXPORT bool IsDark(SkColor color); 125 126 // Returns whichever of white or the darkest available color contrasts more with 127 // |color|. 128 GFX_EXPORT SkColor GetColorWithMaxContrast(SkColor color); 129 130 // Returns whichever of white or the darkest available color contrasts less with 131 // |color|. 132 GFX_EXPORT SkColor GetEndpointColorWithMinContrast(SkColor color); 133 134 // Blends towards the color with max contrast by |alpha|. The alpha of 135 // the original color is preserved. 136 GFX_EXPORT SkColor BlendTowardMaxContrast(SkColor color, SkAlpha alpha); 137 138 // Returns whichever of |foreground1| or |foreground2| has higher contrast with 139 // |background|. 140 GFX_EXPORT SkColor PickContrastingColor(SkColor foreground1, 141 SkColor foreground2, 142 SkColor background); 143 144 // Alpha-blends |default_foreground| toward either |high_contrast_foreground| 145 // (if specified) or the color with max contrast with |background| until either 146 // the result has a contrast ratio against |background| of at least 147 // |contrast_ratio| or the blend can go no further. Returns the blended color 148 // and the alpha used to achieve that blend. If |default_foreground| already 149 // has sufficient contrast, returns an alpha of 0 and color of 150 // |default_foreground|. 151 GFX_EXPORT BlendResult BlendForMinContrast( 152 SkColor default_foreground, 153 SkColor background, 154 base::Optional<SkColor> high_contrast_foreground = base::nullopt, 155 float contrast_ratio = kMinimumReadableContrastRatio); 156 157 // Invert a color. 158 GFX_EXPORT SkColor InvertColor(SkColor color); 159 160 // Gets a Windows system color as a SkColor 161 GFX_EXPORT SkColor GetSysSkColor(int which); 162 163 // Derives a color for icons on a UI surface based on the text color on the same 164 // surface. 165 GFX_EXPORT SkColor DeriveDefaultIconColor(SkColor text_color); 166 167 // Creates an rgba string for an SkColor. For example: 'rgba(255,0,255,0.5)'. 168 GFX_EXPORT std::string SkColorToRgbaString(SkColor color); 169 170 // Creates an rgb string for an SkColor. For example: '255,0,255'. 171 GFX_EXPORT std::string SkColorToRgbString(SkColor color); 172 173 // Sets the darkest available color to |color|. Returns the previous darkest 174 // color. 175 GFX_EXPORT SkColor SetDarkestColorForTesting(SkColor color); 176 177 // Returns the luminance of the darkest, midpoint, and lightest colors. 178 GFX_EXPORT std::tuple<float, float, float> GetLuminancesForTesting(); 179 180 } // namespace color_utils 181 182 #endif // UI_GFX_COLOR_UTILS_H_ 183