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// 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 "ui/gfx/color_utils.h"
#include <stdint.h>
#include <algorithm>
#include <cmath>
#include "base/logging.h"
#include "base/numerics/safe_conversions.h"
#include "base/strings/string_number_conversions.h"
#include "base/strings/stringprintf.h"
#include "build/build_config.h"
#include "third_party/skia/include/core/SkBitmap.h"
#include "ui/gfx/color_palette.h"
#include "ui/gfx/geometry/safe_integer_conversions.h"
#if defined(OS_WIN)
#include <windows.h>
#include "skia/ext/skia_utils_win.h"
#endif
namespace color_utils {
namespace {
// The darkest reference color in color_utils.
SkColor g_darkest_color = gfx::kGoogleGrey900;
// The luminance midpoint for determining if a color is light or dark. This is
// the value where white and g_darkest_color contrast equally. This default
// value is the midpoint given kGoogleGrey900 as the darkest color.
float g_luminance_midpoint = 0.211692036f;
constexpr float kWhiteLuminance = 1.0f;
int calcHue(float temp1, float temp2, float hue) {
if (hue < 0.0f)
++hue;
else if (hue > 1.0f)
--hue;
float result = temp1;
if (hue * 6.0f < 1.0f)
result = temp1 + (temp2 - temp1) * hue * 6.0f;
else if (hue * 2.0f < 1.0f)
result = temp2;
else if (hue * 3.0f < 2.0f)
result = temp1 + (temp2 - temp1) * (2.0f / 3.0f - hue) * 6.0f;
return static_cast<int>(std::round(result * 255));
}
// Assumes sRGB.
float Linearize(float eight_bit_component) {
const float component = eight_bit_component / 255.0f;
// The W3C link in the header uses 0.03928 here. See
// https://en.wikipedia.org/wiki/SRGB#Theory_of_the_transformation for
// discussion of why we use this value rather than that one.
return (component <= 0.04045f) ? (component / 12.92f)
: pow((component + 0.055f) / 1.055f, 2.4f);
}
} // namespace
float GetContrastRatio(SkColor color_a, SkColor color_b) {
return GetContrastRatio(GetRelativeLuminance(color_a),
GetRelativeLuminance(color_b));
}
float GetContrastRatio(float luminance_a, float luminance_b) {
DCHECK_GE(luminance_a, 0.0f);
DCHECK_GE(luminance_b, 0.0f);
luminance_a += 0.05f;
luminance_b += 0.05f;
return (luminance_a > luminance_b) ? (luminance_a / luminance_b)
: (luminance_b / luminance_a);
}
float GetRelativeLuminance(SkColor color) {
return (0.2126f * Linearize(SkColorGetR(color))) +
(0.7152f * Linearize(SkColorGetG(color))) +
(0.0722f * Linearize(SkColorGetB(color)));
}
uint8_t GetLuma(SkColor color) {
return static_cast<uint8_t>(std::round((0.299f * SkColorGetR(color)) +
(0.587f * SkColorGetG(color)) +
(0.114f * SkColorGetB(color))));
}
void SkColorToHSL(SkColor c, HSL* hsl) {
float r = SkColorGetR(c) / 255.0f;
float g = SkColorGetG(c) / 255.0f;
float b = SkColorGetB(c) / 255.0f;
float vmax = std::max({r, g, b});
float vmin = std::min({r, g, b});
float delta = vmax - vmin;
hsl->l = (vmax + vmin) / 2;
if (SkColorGetR(c) == SkColorGetG(c) && SkColorGetR(c) == SkColorGetB(c)) {
hsl->h = hsl->s = 0;
} else {
float dr = (((vmax - r) / 6.0f) + (delta / 2.0f)) / delta;
float dg = (((vmax - g) / 6.0f) + (delta / 2.0f)) / delta;
float db = (((vmax - b) / 6.0f) + (delta / 2.0f)) / delta;
// We need to compare for the max value because comparing vmax to r, g, or b
// can sometimes result in values overflowing registers.
if (r >= g && r >= b)
hsl->h = db - dg;
else if (g >= r && g >= b)
hsl->h = (1.0f / 3.0f) + dr - db;
else // (b >= r && b >= g)
hsl->h = (2.0f / 3.0f) + dg - dr;
if (hsl->h < 0.0f)
++hsl->h;
else if (hsl->h > 1.0f)
--hsl->h;
hsl->s = delta / ((hsl->l < 0.5f) ? (vmax + vmin) : (2 - vmax - vmin));
}
}
SkColor HSLToSkColor(const HSL& hsl, SkAlpha alpha) {
float hue = hsl.h;
float saturation = hsl.s;
float lightness = hsl.l;
// If there's no color, we don't care about hue and can do everything based on
// brightness.
if (!saturation) {
const uint8_t light =
base::saturated_cast<uint8_t>(gfx::ToRoundedInt(lightness * 255));
return SkColorSetARGB(alpha, light, light, light);
}
float temp2 = (lightness < 0.5f)
? (lightness * (1.0f + saturation))
: (lightness + saturation - (lightness * saturation));
float temp1 = 2.0f * lightness - temp2;
return SkColorSetARGB(alpha, calcHue(temp1, temp2, hue + 1.0f / 3.0f),
calcHue(temp1, temp2, hue),
calcHue(temp1, temp2, hue - 1.0f / 3.0f));
}
bool IsWithinHSLRange(const HSL& hsl,
const HSL& lower_bound,
const HSL& upper_bound) {
DCHECK(hsl.h >= 0 && hsl.h <= 1) << hsl.h;
DCHECK(hsl.s >= 0 && hsl.s <= 1) << hsl.s;
DCHECK(hsl.l >= 0 && hsl.l <= 1) << hsl.l;
DCHECK(lower_bound.h < 0 || upper_bound.h < 0 ||
(lower_bound.h <= 1 && upper_bound.h <= lower_bound.h + 1))
<< "lower_bound.h: " << lower_bound.h
<< ", upper_bound.h: " << upper_bound.h;
DCHECK(lower_bound.s < 0 || upper_bound.s < 0 ||
(lower_bound.s <= upper_bound.s && upper_bound.s <= 1))
<< "lower_bound.s: " << lower_bound.s
<< ", upper_bound.s: " << upper_bound.s;
DCHECK(lower_bound.l < 0 || upper_bound.l < 0 ||
(lower_bound.l <= upper_bound.l && upper_bound.l <= 1))
<< "lower_bound.l: " << lower_bound.l
<< ", upper_bound.l: " << upper_bound.l;
// If the upper hue is >1, the given hue bounds wrap around at 1.
bool matches_hue = upper_bound.h > 1
? hsl.h >= lower_bound.h || hsl.h <= upper_bound.h - 1
: hsl.h >= lower_bound.h && hsl.h <= upper_bound.h;
return (upper_bound.h < 0 || lower_bound.h < 0 || matches_hue) &&
(upper_bound.s < 0 || lower_bound.s < 0 ||
(hsl.s >= lower_bound.s && hsl.s <= upper_bound.s)) &&
(upper_bound.l < 0 || lower_bound.l < 0 ||
(hsl.l >= lower_bound.l && hsl.l <= upper_bound.l));
}
void MakeHSLShiftValid(HSL* hsl) {
if (hsl->h < 0 || hsl->h > 1)
hsl->h = -1;
if (hsl->s < 0 || hsl->s > 1)
hsl->s = -1;
if (hsl->l < 0 || hsl->l > 1)
hsl->l = -1;
}
bool IsHSLShiftMeaningful(const HSL& hsl) {
// -1 in any channel has no effect, and 0.5 has no effect for S/L. A shift
// with an effective value in ANY channel is meaningful.
return hsl.h != -1 || (hsl.s != -1 && hsl.s != 0.5) ||
(hsl.l != -1 && hsl.l != 0.5);
}
SkColor HSLShift(SkColor color, const HSL& shift) {
SkAlpha alpha = SkColorGetA(color);
if (shift.h >= 0 || shift.s >= 0) {
HSL hsl;
SkColorToHSL(color, &hsl);
// Replace the hue with the tint's hue.
if (shift.h >= 0)
hsl.h = shift.h;
// Change the saturation.
if (shift.s >= 0) {
if (shift.s <= 0.5f)
hsl.s *= shift.s * 2.0f;
else
hsl.s += (1.0f - hsl.s) * ((shift.s - 0.5f) * 2.0f);
}
color = HSLToSkColor(hsl, alpha);
}
if (shift.l < 0)
return color;
// Lightness shifts in the style of popular image editors aren't actually
// represented in HSL - the L value does have some effect on saturation.
float r = static_cast<float>(SkColorGetR(color));
float g = static_cast<float>(SkColorGetG(color));
float b = static_cast<float>(SkColorGetB(color));
if (shift.l <= 0.5f) {
r *= (shift.l * 2.0f);
g *= (shift.l * 2.0f);
b *= (shift.l * 2.0f);
} else {
r += (255.0f - r) * ((shift.l - 0.5f) * 2.0f);
g += (255.0f - g) * ((shift.l - 0.5f) * 2.0f);
b += (255.0f - b) * ((shift.l - 0.5f) * 2.0f);
}
return SkColorSetARGB(alpha,
static_cast<int>(std::round(r)),
static_cast<int>(std::round(g)),
static_cast<int>(std::round(b)));
}
void BuildLumaHistogram(const SkBitmap& bitmap, int histogram[256]) {
DCHECK_EQ(kN32_SkColorType, bitmap.colorType());
int pixel_width = bitmap.width();
int pixel_height = bitmap.height();
for (int y = 0; y < pixel_height; ++y) {
for (int x = 0; x < pixel_width; ++x)
++histogram[GetLuma(bitmap.getColor(x, y))];
}
}
double CalculateBoringScore(const SkBitmap& bitmap) {
if (bitmap.isNull() || bitmap.empty())
return 1.0;
int histogram[256] = {0};
BuildLumaHistogram(bitmap, histogram);
int color_count = *std::max_element(histogram, histogram + 256);
int pixel_count = bitmap.width() * bitmap.height();
return static_cast<double>(color_count) / pixel_count;
}
SkColor AlphaBlend(SkColor foreground, SkColor background, SkAlpha alpha) {
return AlphaBlend(foreground, background, alpha / 255.0f);
}
SkColor AlphaBlend(SkColor foreground, SkColor background, float alpha) {
DCHECK_GE(alpha, 0.0f);
DCHECK_LE(alpha, 1.0f);
if (alpha == 0.0f)
return background;
if (alpha == 1.0f)
return foreground;
int f_alpha = SkColorGetA(foreground);
int b_alpha = SkColorGetA(background);
float normalizer = f_alpha * alpha + b_alpha * (1.0f - alpha);
if (normalizer == 0.0f)
return SK_ColorTRANSPARENT;
float f_weight = f_alpha * alpha / normalizer;
float b_weight = b_alpha * (1.0f - alpha) / normalizer;
float r =
SkColorGetR(foreground) * f_weight + SkColorGetR(background) * b_weight;
float g =
SkColorGetG(foreground) * f_weight + SkColorGetG(background) * b_weight;
float b =
SkColorGetB(foreground) * f_weight + SkColorGetB(background) * b_weight;
return SkColorSetARGB(gfx::ToRoundedInt(normalizer), gfx::ToRoundedInt(r),
gfx::ToRoundedInt(g), gfx::ToRoundedInt(b));
}
SkColor GetResultingPaintColor(SkColor foreground, SkColor background) {
return AlphaBlend(SkColorSetA(foreground, SK_AlphaOPAQUE), background,
SkAlpha{SkColorGetA(foreground)});
}
bool IsDark(SkColor color) {
return GetRelativeLuminance(color) < g_luminance_midpoint;
}
SkColor GetColorWithMaxContrast(SkColor color) {
return IsDark(color) ? SK_ColorWHITE : g_darkest_color;
}
SkColor BlendTowardMaxContrast(SkColor color, SkAlpha alpha) {
SkAlpha original_alpha = SkColorGetA(color);
SkColor blended_color = AlphaBlend(GetColorWithMaxContrast(color),
SkColorSetA(color, SK_AlphaOPAQUE), alpha);
return SkColorSetA(blended_color, original_alpha);
}
SkColor PickContrastingColor(SkColor foreground1,
SkColor foreground2,
SkColor background) {
const float background_luminance = GetRelativeLuminance(background);
return (GetContrastRatio(GetRelativeLuminance(foreground1),
background_luminance) >=
GetContrastRatio(GetRelativeLuminance(foreground2),
background_luminance)) ?
foreground1 : foreground2;
}
SkColor GetColorWithMinimumContrast(SkColor default_foreground,
SkColor background) {
const SkColor contrasting_color = GetColorWithMaxContrast(background);
const SkAlpha alpha = GetBlendValueWithMinimumContrast(
default_foreground, contrasting_color, background,
kMinimumReadableContrastRatio);
return AlphaBlend(contrasting_color, default_foreground, alpha);
}
SkAlpha GetBlendValueWithMinimumContrast(SkColor source,
SkColor target,
SkColor base,
float contrast_ratio) {
DCHECK_EQ(SkColorGetA(base), SK_AlphaOPAQUE);
source = GetResultingPaintColor(source, base);
if (GetContrastRatio(source, base) >= contrast_ratio)
return 0;
target = GetResultingPaintColor(target, base);
constexpr int kCloseEnoughAlphaDelta = 0x04;
return FindBlendValueForContrastRatio(source, target, base, contrast_ratio,
kCloseEnoughAlphaDelta);
}
SkAlpha FindBlendValueForContrastRatio(SkColor source,
SkColor target,
SkColor base,
float contrast_ratio,
int alpha_error_tolerance) {
DCHECK_EQ(SkColorGetA(source), SK_AlphaOPAQUE);
DCHECK_EQ(SkColorGetA(target), SK_AlphaOPAQUE);
DCHECK_EQ(SkColorGetA(base), SK_AlphaOPAQUE);
DCHECK_GE(alpha_error_tolerance, 0);
const float base_luminance = GetRelativeLuminance(base);
// Use int for inclusive lower bound and exclusive upper bound, reserving
// conversion to SkAlpha for the end (reduces casts).
int low = SK_AlphaTRANSPARENT;
int high = SK_AlphaOPAQUE + 1;
SkAlpha best = SK_AlphaOPAQUE;
while (low + alpha_error_tolerance < high) {
const SkAlpha alpha = (low + high) / 2;
const SkColor blended = AlphaBlend(target, source, alpha);
const float luminance = GetRelativeLuminance(blended);
const float contrast = GetContrastRatio(luminance, base_luminance);
if (contrast >= contrast_ratio) {
best = alpha;
high = alpha;
} else {
low = alpha + 1;
}
}
return best;
}
SkColor InvertColor(SkColor color) {
return SkColorSetARGB(SkColorGetA(color), 255 - SkColorGetR(color),
255 - SkColorGetG(color), 255 - SkColorGetB(color));
}
SkColor GetSysSkColor(int which) {
#if defined(OS_WIN)
return skia::COLORREFToSkColor(GetSysColor(which));
#else
NOTIMPLEMENTED();
return SK_ColorLTGRAY;
#endif
}
// OS_WIN implementation lives in sys_color_change_listener.cc
#if !defined(OS_WIN)
bool IsInvertedColorScheme() {
return false;
}
#endif // !defined(OS_WIN)
SkColor DeriveDefaultIconColor(SkColor text_color) {
// Lighten dark colors and brighten light colors. The alpha value here (0x4c)
// is chosen to generate a value close to GoogleGrey700 from GoogleGrey900.
return BlendTowardMaxContrast(text_color, 0x4c);
}
std::string SkColorToRgbaString(SkColor color) {
// We convert the alpha using NumberToString because StringPrintf will use
// locale specific formatters (e.g., use , instead of . in German).
return base::StringPrintf(
"rgba(%s,%s)", SkColorToRgbString(color).c_str(),
base::NumberToString(SkColorGetA(color) / 255.0).c_str());
}
std::string SkColorToRgbString(SkColor color) {
return base::StringPrintf("%d,%d,%d", SkColorGetR(color), SkColorGetG(color),
SkColorGetB(color));
}
SkColor SetDarkestColorForTesting(SkColor color) {
const SkColor previous_darkest_color = g_darkest_color;
g_darkest_color = color;
const float dark_luminance = GetRelativeLuminance(color);
// We want to compute |g_luminance_midpoint| such that
// GetContrastRatio(dark_luminance, g_luminance_midpoint) ==
// GetContrastRatio(kWhiteLuminance, g_luminance_midpoint). The formula below
// can be verified by plugging it into how GetContrastRatio() operates.
g_luminance_midpoint =
sqrtf((dark_luminance + 0.05f) * (kWhiteLuminance + 0.05f)) - 0.05f;
return previous_darkest_color;
}
std::tuple<float, float, float> GetLuminancesForTesting() {
return std::make_tuple(GetRelativeLuminance(g_darkest_color),
g_luminance_midpoint, kWhiteLuminance);
}
} // namespace color_utils
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