| // Copyright (c) 2012 The Chromium Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #ifndef UI_GFX_COLOR_UTILS_H_ |
| #define UI_GFX_COLOR_UTILS_H_ |
| |
| #include <string> |
| #include <tuple> |
| |
| #include "third_party/skia/include/core/SkColor.h" |
| #include "ui/gfx/gfx_export.h" |
| |
| class SkBitmap; |
| |
| namespace color_utils { |
| |
| // Represents an HSL color. |
| struct HSL { |
| double h; |
| double s; |
| double l; |
| }; |
| |
| // The minimum contrast between text and background that is still readable. |
| // This value is taken from w3c accessibility guidelines. |
| constexpr float kMinimumReadableContrastRatio = 4.5f; |
| |
| // Determines the contrast ratio of two colors or two relative luminance values |
| // (as computed by RelativeLuminance()), calculated according to |
| // http://www.w3.org/TR/WCAG20/#contrast-ratiodef . |
| GFX_EXPORT float GetContrastRatio(SkColor color_a, SkColor color_b); |
| GFX_EXPORT float GetContrastRatio(float luminance_a, float luminance_b); |
| |
| // The relative luminance of |color|, that is, the weighted sum of the |
| // linearized RGB components, normalized to 0..1, per BT.709. See |
| // http://www.w3.org/TR/WCAG20/#relativeluminancedef . |
| GFX_EXPORT float GetRelativeLuminance(SkColor color); |
| |
| // The luma of |color|, that is, the weighted sum of the gamma-compressed R'G'B' |
| // components, per BT.601, a.k.a. the Y' in Y'UV. See |
| // https://en.wikipedia.org/wiki/Luma_(video). |
| GFX_EXPORT uint8_t GetLuma(SkColor color); |
| |
| // Note: these transformations assume sRGB as the source color space |
| GFX_EXPORT void SkColorToHSL(SkColor c, HSL* hsl); |
| GFX_EXPORT SkColor HSLToSkColor(const HSL& hsl, SkAlpha alpha); |
| |
| // Determines whether the given |hsl| falls within the given range for each |
| // component. All components of |hsl| are expected to be in the range [0, 1]. |
| // |
| // If a component is negative in either |lower_bound| or |upper_bound|, that |
| // component will be ignored. |
| // |
| // For hue, the lower bound should be in the range [0, 1] and the upper bound |
| // should be in the range [(lower bound), (lower bound + 1)]. |
| // For saturation and value, bounds should be specified in the range [0, 1], |
| // with the lower bound less than the upper bound. |
| GFX_EXPORT bool IsWithinHSLRange(const HSL& hsl, |
| const HSL& lower_bound, |
| const HSL& upper_bound); |
| |
| // Makes |hsl| valid input for HSLShift(). Sets values of hue, saturation |
| // and lightness which are outside of the valid range [0, 1] to -1. -1 is a |
| // special value which indicates 'no change'. |
| GFX_EXPORT void MakeHSLShiftValid(HSL* hsl); |
| |
| // Returns whether pasing |hsl| to HSLShift() would have any effect. Assumes |
| // |hsl| is a valid shift (as defined by MakeHSLShiftValid()). |
| GFX_EXPORT bool IsHSLShiftMeaningful(const HSL& hsl); |
| |
| // HSL-Shift an SkColor. The shift values are in the range of 0-1, with the |
| // option to specify -1 for 'no change'. The shift values are defined as: |
| // hsl_shift[0] (hue): The absolute hue value - 0 and 1 map |
| // to 0 and 360 on the hue color wheel (red). |
| // hsl_shift[1] (saturation): A saturation shift, with the |
| // following key values: |
| // 0 = remove all color. |
| // 0.5 = leave unchanged. |
| // 1 = fully saturate the image. |
| // hsl_shift[2] (lightness): A lightness shift, with the |
| // following key values: |
| // 0 = remove all lightness (make all pixels black). |
| // 0.5 = leave unchanged. |
| // 1 = full lightness (make all pixels white). |
| GFX_EXPORT SkColor HSLShift(SkColor color, const HSL& shift); |
| |
| // Builds a histogram based on the Y' of the Y'UV representation of this image. |
| GFX_EXPORT void BuildLumaHistogram(const SkBitmap& bitmap, int histogram[256]); |
| |
| // Calculates how "boring" an image is. The boring score is the |
| // 0,1 ranged percentage of pixels that are the most common |
| // luma. Higher boring scores indicate that a higher percentage of a |
| // bitmap are all the same brightness. |
| GFX_EXPORT double CalculateBoringScore(const SkBitmap& bitmap); |
| |
| // Returns a blend of the supplied colors, ranging from |background| (for |
| // |alpha| == 0) to |foreground| (for |alpha| == 255). The alpha channels of |
| // the supplied colors are also taken into account, so the returned color may |
| // be partially transparent. |
| GFX_EXPORT SkColor AlphaBlend(SkColor foreground, |
| SkColor background, |
| SkAlpha alpha); |
| |
| // As above, but with alpha specified as 0..1. |
| GFX_EXPORT SkColor AlphaBlend(SkColor foreground, |
| SkColor background, |
| float alpha); |
| |
| // Returns the color that results from painting |foreground| on top of |
| // |background|. |
| GFX_EXPORT SkColor GetResultingPaintColor(SkColor foreground, |
| SkColor background); |
| |
| // Returns true if |color| contrasts more with white than the darkest color. |
| GFX_EXPORT bool IsDark(SkColor color); |
| |
| // Returns whichever of white or the darkest available color contrasts more with |
| // |color|. |
| GFX_EXPORT SkColor GetColorWithMaxContrast(SkColor color); |
| |
| // Blends towards the color with max contrast by |alpha|. The alpha of |
| // the original color is preserved. |
| GFX_EXPORT SkColor BlendTowardMaxContrast(SkColor color, SkAlpha alpha); |
| |
| // Returns whichever of |foreground1| or |foreground2| has higher contrast with |
| // |background|. |
| GFX_EXPORT SkColor PickContrastingColor(SkColor foreground1, |
| SkColor foreground2, |
| SkColor background); |
| |
| // This function attempts to select a color based on |default_foreground| that |
| // will meet the minimum contrast ratio when used as a text color on top of |
| // |background|. If |default_foreground| already meets the minimum contrast |
| // ratio, this function will simply return it. Otherwise it will blend the color |
| // darker/lighter until either the contrast ratio is acceptable or the color |
| // cannot become any more extreme. Only use with opaque background. |
| GFX_EXPORT SkColor GetColorWithMinimumContrast(SkColor default_foreground, |
| SkColor background); |
| |
| // Attempts to select an alpha value such that blending |target| onto |source| |
| // with that alpha produces a color of at least |contrast_ratio| against |base|. |
| // If |source| already meets the minimum contrast ratio, this function will |
| // simply return 0. Otherwise it will blend the |target| onto |source| until |
| // either the contrast ratio is acceptable or the color cannot become any more |
| // extreme. |base| must be opaque. |
| GFX_EXPORT SkAlpha GetBlendValueWithMinimumContrast(SkColor source, |
| SkColor target, |
| SkColor base, |
| float contrast_ratio); |
| |
| // Returns the minimum alpha value such that blending |target| onto |source| |
| // produces a color that contrasts against |base| with at least |contrast_ratio| |
| // unless this is impossible, in which case SK_AlphaOPAQUE is returned. |
| // Use only with opaque colors. |alpha_error_tolerance| should normally be 0 for |
| // best accuracy, but if performance is critical then it can be a positive value |
| // (4 is recommended) to save a few cycles and give "close enough" alpha. |
| GFX_EXPORT SkAlpha FindBlendValueForContrastRatio(SkColor source, |
| SkColor target, |
| SkColor base, |
| float contrast_ratio, |
| int alpha_error_tolerance); |
| |
| // Invert a color. |
| GFX_EXPORT SkColor InvertColor(SkColor color); |
| |
| // Gets a Windows system color as a SkColor |
| GFX_EXPORT SkColor GetSysSkColor(int which); |
| |
| // Returns true only if Chrome should use an inverted color scheme - which is |
| // only true if the system has high-contrast mode enabled and and is using a |
| // light-on-dark color scheme. |
| GFX_EXPORT bool IsInvertedColorScheme(); |
| |
| // Derives a color for icons on a UI surface based on the text color on the same |
| // surface. |
| GFX_EXPORT SkColor DeriveDefaultIconColor(SkColor text_color); |
| |
| // Creates an rgba string for an SkColor. For example: 'rgba(255,0,255,0.5)'. |
| GFX_EXPORT std::string SkColorToRgbaString(SkColor color); |
| |
| // Creates an rgb string for an SkColor. For example: '255,0,255'. |
| GFX_EXPORT std::string SkColorToRgbString(SkColor color); |
| |
| // Sets the darkest available color to |color|. Returns the previous darkest |
| // color. |
| GFX_EXPORT SkColor SetDarkestColorForTesting(SkColor color); |
| |
| // Returns the luminance of the darkest, midpoint, and lightest colors. |
| GFX_EXPORT std::tuple<float, float, float> GetLuminancesForTesting(); |
| |
| } // namespace color_utils |
| |
| #endif // UI_GFX_COLOR_UTILS_H_ |