72 lines
2.9 KiB
C++
72 lines
2.9 KiB
C++
/*
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* Copyright (C) 2021 Apple Inc. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
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* THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
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* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
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* THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#pragma once
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#include "ColorConversion.h"
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namespace WebCore {
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class Color;
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template<typename ColorType> inline double relativeLuminance(const ColorType& color)
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{
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// https://en.wikipedia.org/wiki/Relative_luminance
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// FIXME: This can be optimized a bit by observing that in some cases the conversion
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// to XYZA<float, WhitePoint::D65> in its entirety is unnecessary to get just the Y
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// component. For instance, for SRGBA<float>, this could be done as:
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//
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// convertColor<LinearSRGBA<float>>(color) * LinearSRGBA<float>::linearToXYZ.row(1)
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//
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// (for a hypothetical row() function on ColorMatrix). We would probably want to implement
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// this in ColorConversion.h as a sibling function to convertColor which can get a channel
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// of a color in another space in this kind of optimal way.
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return convertColor<XYZA<float, WhitePoint::D65>>(color).y;
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}
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inline double contrastRatio(double relativeLuminanceA, double relativeLuminanceB)
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{
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// Uses the WCAG 2.0 definition of contrast ratio.
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// https://www.w3.org/TR/WCAG20/#contrast-ratiodef
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auto lighterLuminance = relativeLuminanceA;
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auto darkerLuminance = relativeLuminanceB;
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if (lighterLuminance < darkerLuminance)
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std::swap(lighterLuminance, darkerLuminance);
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return (lighterLuminance + 0.05) / (darkerLuminance + 0.05);
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}
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template<typename ColorTypeA, typename ColorTypeB> inline double contrastRatio(const ColorTypeA& colorA, const ColorTypeB& colorB)
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{
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return contrastRatio(relativeLuminance(colorA), relativeLuminance(colorB));
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}
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double contrastRatio(const Color&, const Color&);
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}
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