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