forked from mirrors/gecko-dev
78 lines
2.6 KiB
C++
78 lines
2.6 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef mozilla_RelativeLuminanceUtils_h
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#define mozilla_RelativeLuminanceUtils_h
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#include "nsColor.h"
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namespace mozilla {
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// Utilities for calculating relative luminance based on the algorithm
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// defined in https://www.w3.org/TR/WCAG20/#relativeluminancedef
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class RelativeLuminanceUtils {
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public:
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// Compute the relative luminance.
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static float Compute(nscolor aColor) {
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float r = ComputeComponent(NS_GET_R(aColor));
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float g = ComputeComponent(NS_GET_G(aColor));
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float b = ComputeComponent(NS_GET_B(aColor));
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return ComputeFromComponents(r, g, b);
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}
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// Adjust the relative luminance of the given color.
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static nscolor Adjust(nscolor aColor, float aLuminance) {
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float r = ComputeComponent(NS_GET_R(aColor));
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float g = ComputeComponent(NS_GET_G(aColor));
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float b = ComputeComponent(NS_GET_B(aColor));
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float luminance = ComputeFromComponents(r, g, b);
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float factor = (aLuminance + 0.05f) / (luminance + 0.05f);
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uint8_t r1 =
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DecomputeComponent(std::max(0.0f, (r + 0.05f) * factor - 0.05f));
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uint8_t g1 =
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DecomputeComponent(std::max(0.0f, (g + 0.05f) * factor - 0.05f));
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uint8_t b1 =
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DecomputeComponent(std::max(0.0f, (b + 0.05f) * factor - 0.05f));
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return NS_RGBA(r1, g1, b1, NS_GET_A(aColor));
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}
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// https://www.w3.org/TR/WCAG21/#dfn-contrast-ratio
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static float ContrastRatio(nscolor aColor1, nscolor aColor2) {
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float l1 = Compute(aColor1);
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float l2 = Compute(aColor2);
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if (l1 < l2) {
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std::swap(l1, l2);
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}
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return (l1 + 0.05f) / (l2 + 0.05f);
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}
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private:
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static float ComputeComponent(uint8_t aComponent) {
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float v = float(aComponent) / 255.0f;
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if (v <= 0.03928f) {
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return v / 12.92f;
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}
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return std::pow((v + 0.055f) / 1.055f, 2.4f);
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}
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static constexpr float ComputeFromComponents(float aR, float aG, float aB) {
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return 0.2126f * aR + 0.7152f * aG + 0.0722f * aB;
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}
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// Inverse function of ComputeComponent.
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static uint8_t DecomputeComponent(float aComponent) {
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if (aComponent <= 0.03928f / 12.92f) {
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aComponent *= 12.92f;
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} else {
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aComponent = std::pow(aComponent, 1.0f / 2.4f) * 1.055f - 0.055f;
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}
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return ClampColor(aComponent * 255.0f);
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}
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};
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} // namespace mozilla
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#endif // mozilla_RelativeLuminanceUtils_h
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