blob: 5838b5279ebc6e73415d7b221340fbf0438af192 [file] [log] [blame]
// 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.
#include <string>
#include <tuple>
#include "base/optional.h"
#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 blend alpha and resulting color when blending to achieve a desired
// contrast raio.
struct BlendResult {
SkAlpha alpha;
SkColor color;
// 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
// .
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
// .
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
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);
// Returns whichever of white or the darkest available color contrasts less with
// |color|.
GFX_EXPORT SkColor GetEndpointColorWithMinContrast(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);
// Alpha-blends |default_foreground| toward either |high_contrast_foreground|
// (if specified) or the color with max contrast with |background| until either
// the result has a contrast ratio against |background| of at least
// |contrast_ratio| or the blend can go no further. Returns the blended color
// and the alpha used to achieve that blend. If |default_foreground| already
// has sufficient contrast, returns an alpha of 0 and color of
// |default_foreground|.
GFX_EXPORT BlendResult BlendForMinContrast(
SkColor default_foreground,
SkColor background,
base::Optional<SkColor> high_contrast_foreground = base::nullopt,
float contrast_ratio = kMinimumReadableContrastRatio);
// Invert a color.
GFX_EXPORT SkColor InvertColor(SkColor color);
// Gets a Windows system color as a SkColor
GFX_EXPORT SkColor GetSysSkColor(int which);
// 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