ColorUtilities.h   [plain text]

/*
 * Copyright (C) 2017, 2020 Apple Inc. All rights reserved.
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 *     notice, this list of conditions and the following disclaimer in the
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 *
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 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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 */

#pragma once

#include "ColorTypes.h"
#include <algorithm>
#include <cmath>
#include <functional>
#include <math.h>

namespace WebCore {

template<typename> struct SRGBA;

float lightness(const SRGBA<float>&);
float luminance(const SRGBA<float>&);
float contrastRatio(const SRGBA<float>&, const SRGBA<float>&);

SRGBA<float> premultiplied(const SRGBA<float>&);
SRGBA<float> unpremultiplied(const SRGBA<float>&);

SRGBA<uint8_t> premultipliedFlooring(SRGBA<uint8_t>);
SRGBA<uint8_t> premultipliedCeiling(SRGBA<uint8_t>);
SRGBA<uint8_t> unpremultiplied(SRGBA<uint8_t>);

uint8_t convertPrescaledToComponentByte(float);

uint8_t convertToComponentByte(float);
constexpr float convertToComponentFloat(uint8_t);

template<typename ComponentType> constexpr uint8_t clampToComponentByte(ComponentType);
template<typename ComponentType> constexpr float clampToComponentFloat(ComponentType);

template<typename T> T convertComponentByteTo(uint8_t);
template<typename T> T convertComponentFloatTo(float);

template<template<typename> typename ColorType> ColorType<uint8_t> convertToComponentBytes(const ColorType<float>&);
template<template<typename> typename ColorType> constexpr ColorType<float> convertToComponentFloats(const ColorType<uint8_t>&);

template<template<typename> typename ColorType, typename... ComponentType> constexpr ColorType<uint8_t> clampToComponentBytes(ComponentType...);
template<template<typename> typename ColorType, typename... ComponentType> constexpr ColorType<float> clampToComponentFloats(ComponentType...);

template<typename ColorType, typename Functor> ColorType colorByModifingEachNonAlphaComponent(const ColorType&, Functor&&);

template<typename ColorType> constexpr ColorType colorWithOverridenAlpha(const ColorType&, uint8_t overrideAlpha);
template<typename ColorType> ColorType colorWithOverridenAlpha(const ColorType&, float overrideAlpha);

template<typename ColorType> constexpr ColorType invertedColorWithOverridenAlpha(const ColorType&, uint8_t overrideAlpha);
template<typename ColorType> ColorType invertedColorWithOverridenAlpha(const ColorType&, float overrideAlpha);

template<typename ColorType> constexpr bool isBlack(const ColorType&);
template<typename ColorType> constexpr bool isWhite(const ColorType&);

constexpr uint16_t fastMultiplyBy255(uint16_t);
constexpr uint16_t fastDivideBy255(uint16_t);


inline uint8_t convertPrescaledToComponentByte(float f)
{
    return std::clamp(std::lround(f), 0l, 255l);
}

inline uint8_t convertToComponentByte(float f)
{
    return std::clamp(std::lround(f * 255.0f), 0l, 255l);
}

constexpr float convertToComponentFloat(uint8_t byte)
{
    return byte / 255.0f;
}

template<typename ComponentType> constexpr uint8_t clampToComponentByte(ComponentType component)
{
    return std::clamp<ComponentType>(component, 0, 255);
}

template<typename ComponentType> constexpr float clampToComponentFloat(ComponentType component)
{
    return std::clamp<ComponentType>(component, 0, 1);
}

template<> constexpr uint8_t convertComponentByteTo<uint8_t>(uint8_t value)
{
    return value;
}

template<> constexpr float convertComponentByteTo<float>(uint8_t value)
{
    return convertToComponentFloat(value);
}

template<> inline uint8_t convertComponentFloatTo<uint8_t>(float value)
{
    return convertToComponentByte(value);
}

template<> inline float convertComponentFloatTo<float>(float value)
{
    return clampToComponentFloat(value);
}

template<template<typename> typename ColorType> inline ColorType<uint8_t> convertToComponentBytes(const ColorType<float>& color)
{
    auto components = asColorComponents(color);
    return { convertToComponentByte(components[0]), convertToComponentByte(components[1]), convertToComponentByte(components[2]), convertToComponentByte(components[3]) };
}

template<template<typename> typename ColorType> constexpr ColorType<float> convertToComponentFloats(const ColorType<uint8_t>& color)
{
    auto components = asColorComponents(color);
    return { convertToComponentFloat(components[0]), convertToComponentFloat(components[1]), convertToComponentFloat(components[2]), convertToComponentFloat(components[3]) };
}

template<template<typename> typename ColorType, typename... ComponentType> constexpr ColorType<uint8_t> clampToComponentBytes(ComponentType... components)
{
    return { clampToComponentByte(components)... };
}

template<template<typename> typename ColorType, typename... ComponentType> constexpr ColorType<float> clampToComponentFloats(ComponentType... components)
{
    return { clampToComponentFloat(components)... };
}

template<typename ColorType, typename Functor> ColorType colorByModifingEachNonAlphaComponent(const ColorType& color, Functor&& functor)
{
    // FIXME: This should be made to work with colors that don't use the names red, green, and blue for their channels.
    auto copy = color;
    copy.red = std::invoke(functor, color.red);
    copy.green = std::invoke(functor, color.green);
    copy.blue = std::invoke(std::forward<Functor>(functor), color.blue);
    return copy;
}

template<typename ColorType> constexpr ColorType colorWithOverridenAlpha(const ColorType& color, uint8_t overrideAlpha)
{
    auto copy = color;
    copy.alpha = convertComponentByteTo<decltype(copy.alpha)>(overrideAlpha);
    return copy;
}

template<typename ColorType> ColorType colorWithOverridenAlpha(const ColorType& color, float overrideAlpha)
{
    auto copy = color;
    copy.alpha = convertComponentFloatTo<decltype(copy.alpha)>(overrideAlpha);
    return copy;
}

template<typename ColorType> constexpr ColorType invertedColorWithOverridenAlpha(const ColorType& color, uint8_t overrideAlpha)
{
    auto copy = colorByModifingEachNonAlphaComponent(color, [] (auto component) {
        return ComponentTraits<decltype(component)>::maxValue - component;
    });
    copy.alpha = convertComponentByteTo<decltype(copy.alpha)>(overrideAlpha);
    return copy;
}

template<typename ColorType> ColorType invertedColorWithOverridenAlpha(const ColorType& color, float overrideAlpha)
{
    auto copy = colorByModifingEachNonAlphaComponent(color, [] (auto component) {
        return ComponentTraits<decltype(component)>::maxValue - component;
    });
    copy.alpha = convertComponentFloatTo<decltype(copy.alpha)>(overrideAlpha);
    return copy;
}

template<typename ColorType> constexpr bool isBlack(const ColorType& color)
{
    constexpr auto min = ComponentTraits<typename ColorType::ComponentType>::minValue;
    constexpr auto max = ComponentTraits<typename ColorType::ComponentType>::maxValue;

    auto [c1, c2, c3, alpha] = color;
    return c1 == min && c2 == min && c3 == min && alpha == max;
}

template<typename ColorType> constexpr bool isWhite(const ColorType& color)
{
    constexpr auto max = ComponentTraits<typename ColorType::ComponentType>::maxValue;

    auto [c1, c2, c3, alpha] = color;
    return c1 == max && c2 == max && c3 == max && alpha == max;
}

constexpr uint16_t fastMultiplyBy255(uint16_t value)
{
    return (value << 8) - value;
}

constexpr uint16_t fastDivideBy255(uint16_t value)
{
    // While this is an approximate algorithm for division by 255, it gives perfectly accurate results for 16-bit values.
    // FIXME: Since this gives accurate results for 16-bit values, we should get this optimization into compilers like clang.
    uint16_t approximation = value >> 8;
    uint16_t remainder = value - (approximation * 255) + 1;
    return approximation + (remainder >> 8);
}

} // namespace WebCore