Source/WebCore/platform/graphics/ColorUtilities.h

/*
 * Copyright (C) 2017-2021 Apple Inc. All rights reserved.
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 *     notice, this list of conditions and the following disclaimer in the
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 */

#pragma once

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

namespace WebCore {

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 convertPrescaledSRGBAFloatToSRGBAByte(float);

template<typename T> T convertByteAlphaTo(uint8_t);
template<typename T> T convertFloatAlphaTo(float);

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

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

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

template<typename ColorType, typename std::enable_if_t<UsesLabModel<ColorType> || UsesLCHModel<ColorType>>* = nullptr> constexpr bool isBlack(const ColorType&);
template<typename ColorType, typename std::enable_if_t<UsesRGBModel<ColorType>>* = nullptr> constexpr bool isBlack(const ColorType&);
template<WhitePoint W> constexpr bool isBlack(const XYZA<float, W>&);

template<typename ColorType, typename std::enable_if_t<UsesLabModel<ColorType> || UsesLCHModel<ColorType>>* = nullptr> constexpr bool isWhite(const ColorType&);
template<typename ColorType, typename std::enable_if_t<UsesRGBModel<ColorType>>* = nullptr> constexpr bool isWhite(const ColorType&);
template<WhitePoint W> constexpr bool isWhite(const XYZA<float, W>&);

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


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

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

template<> constexpr float convertByteAlphaTo<float>(uint8_t value)
{
    return value / 255.0f;
}

template<> inline uint8_t convertFloatAlphaTo<uint8_t>(float value)
{
    return std::clamp(std::lround(value * 255.0f), 0l, 255l);
}

template<> inline float convertFloatAlphaTo<float>(float value)
{
    return clampedAlpha(value);
}

template<typename ColorType, typename Functor> ColorType colorByModifingEachNonAlphaComponent(const ColorType& color, Functor&& functor)
{
    auto components = asColorComponents(color);
    auto copy = components;
    copy[0] = std::invoke(functor, components[0]);
    copy[1] = std::invoke(functor, components[1]);
    copy[2] = std::invoke(std::forward<Functor>(functor), components[2]);
    return { copy[0], copy[1], copy[2], copy[3] };
}

template<typename ColorType> constexpr ColorType colorWithOverriddenAlpha(const ColorType& color, uint8_t overrideAlpha)
{
    auto copy = color;
    copy.alpha = convertByteAlphaTo<typename ColorType::ComponentType>(overrideAlpha);
    return copy;
}

template<typename ColorType> ColorType colorWithOverriddenAlpha(const ColorType& color, float overrideAlpha)
{
    auto copy = color;
    copy.alpha = convertFloatAlphaTo<typename ColorType::ComponentType>(overrideAlpha);
    return copy;
}

template<typename ColorType> constexpr ColorType invertedColorWithOverriddenAlpha(const ColorType& color, uint8_t overrideAlpha)
{
    static_assert(ColorType::Model::isInvertible);

    auto components = asColorComponents(color);
    auto copy = components;

    for (unsigned i = 0; i < 3; ++i)
        copy[i] = ColorType::Model::componentInfo[i].max - components[i];
    copy[3] = convertByteAlphaTo<typename ColorType::ComponentType>(overrideAlpha);

    return makeFromComponents<ColorType>(copy);
}

template<typename ColorType> ColorType invertedColorWithOverriddenAlpha(const ColorType& color, float overrideAlpha)
{
    static_assert(ColorType::Model::isInvertible);

    auto components = asColorComponents(color);
    auto copy = components;

    for (unsigned i = 0; i < 3; ++i)
        copy[i] = ColorType::Model::componentInfo[i].max - components[i];
    copy[3] = convertFloatAlphaTo<typename ColorType::ComponentType>(overrideAlpha);

    return makeFromComponents<ColorType>(copy);
}

template<WhitePoint W> constexpr bool isBlack(const XYZA<float, W>& color)
{
    return color.y == 0 && color.alpha == AlphaTraits<float>::opaque;
}

template<typename ColorType, typename std::enable_if_t<UsesLabModel<ColorType> || UsesLCHModel<ColorType>>*>
constexpr bool isBlack(const ColorType& color)
{
    return color.lightness == 0 && color.alpha == AlphaTraits<float>::opaque;
}

template<typename ColorType, typename std::enable_if_t<UsesRGBModel<ColorType>>*>
constexpr bool isBlack(const ColorType& color)
{
    auto [c1, c2, c3, alpha] = color;
    constexpr auto componentInfo = ColorType::Model::componentInfo;
    return c1 == componentInfo[0].min && c2 == componentInfo[1].min && c3 == componentInfo[2].min && alpha == AlphaTraits<typename ColorType::ComponentType>::opaque;
}

template<WhitePoint W> constexpr bool isWhite(const XYZA<float, W>& color)
{
    return color.y == 1 && color.alpha == AlphaTraits<float>::opaque;
}

template<typename ColorType, typename std::enable_if_t<UsesLabModel<ColorType> || UsesLCHModel<ColorType>>*>
constexpr bool isWhite(const ColorType& color)
{
    return color.lightness == 100 && color.alpha == AlphaTraits<float>::opaque;
}

template<typename ColorType, typename std::enable_if_t<UsesRGBModel<ColorType>>*>
constexpr bool isWhite(const ColorType& color)
{
    auto [c1, c2, c3, alpha] = color;
    constexpr auto componentInfo = ColorType::Model::componentInfo;
    return c1 == componentInfo[0].max && c2 == componentInfo[1].max && c3 == componentInfo[2].max && alpha == AlphaTraits<typename ColorType::ComponentType>::opaque;
}

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