color.h

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#ifndef BASE_COLOR_H
#define BASE_COLOR_H
 
#include <base/math.h>
 
#include <algorithm>
#include <optional>
#include <type_traits>
 
/*
    Title: Color handling
*/
/*
    Function: RgbToHue
        Determines the hue from RGB values
*/
constexpr float RgbToHue(float r, float g, float b)
{
    float h_min = std::min({r, g, b});
    float h_max = std::max({r, g, b});
 
    float hue = 0.0f;
    if(h_max != h_min)
    {
        float c = h_max - h_min;
        if(h_max == r)
            hue = (g - b) / c + (g < b ? 6 : 0);
        else if(h_max == g)
            hue = (b - r) / c + 2;
        else
            hue = (r - g) / c + 4;
    }
 
    return hue / 6.0f;
}
 
// Curiously Recurring Template Pattern for type safety
template<typename DerivedT>
class color4_base
{
public:
    union
    {
        float x, r, h;
    };
    union
    {
        float y, g, s;
    };
    union
    {
        float z, b, l, v;
    };
    union
    {
        float w, a;
    };
 
    constexpr color4_base() :
        x(), y(), z(), a()
    {
    }
 
    constexpr color4_base(float nx, float ny, float nz, float na) :
        x(nx), y(ny), z(nz), a(na)
    {
    }
 
    constexpr color4_base(float nx, float ny, float nz) :
        x(nx), y(ny), z(nz), a(1.0f)
    {
    }
 
    constexpr color4_base(unsigned col, bool alpha = false)
    {
        a = alpha ? ((col >> 24) & 0xFF) / 255.0f : 1.0f;
        x = ((col >> 16) & 0xFF) / 255.0f;
        y = ((col >> 8) & 0xFF) / 255.0f;
        z = ((col >> 0) & 0xFF) / 255.0f;
    }
 
    // Disallow casting between different instantiations of the color4_base template.
    // The color_cast functions below should be used to convert between colors.
    template<typename OtherDerivedT>
        requires(!std::is_same_v<DerivedT, OtherDerivedT>)
    color4_base(const color4_base<OtherDerivedT> &Other) = delete;
 
    constexpr float &operator[](int index)
    {
        return ((float *)this)[index];
    }
 
    constexpr bool operator==(const color4_base &col) const { return x == col.x && y == col.y && z == col.z && a == col.a; }
    constexpr bool operator!=(const color4_base &col) const { return x != col.x || y != col.y || z != col.z || a != col.a; }
 
    constexpr unsigned Pack(bool Alpha = true) const
    {
        return (Alpha ? ((unsigned)round_to_int(a * 255.0f) << 24) : 0) + ((unsigned)round_to_int(x * 255.0f) << 16) + ((unsigned)round_to_int(y * 255.0f) << 8) + (unsigned)round_to_int(z * 255.0f);
    }
 
    constexpr unsigned PackAlphaLast(bool Alpha = true) const
    {
        if(Alpha)
            return ((unsigned)round_to_int(x * 255.0f) << 24) + ((unsigned)round_to_int(y * 255.0f) << 16) + ((unsigned)round_to_int(z * 255.0f) << 8) + (unsigned)round_to_int(a * 255.0f);
        return ((unsigned)round_to_int(x * 255.0f) << 16) + ((unsigned)round_to_int(y * 255.0f) << 8) + (unsigned)round_to_int(z * 255.0f);
    }
 
    constexpr DerivedT WithAlpha(float alpha) const
    {
        DerivedT col(static_cast<const DerivedT &>(*this));
        col.a = alpha;
        return col;
    }
 
    constexpr DerivedT WithMultipliedAlpha(float alpha) const
    {
        DerivedT col(static_cast<const DerivedT &>(*this));
        col.a *= alpha;
        return col;
    }
 
    template<typename UnpackT>
    constexpr static UnpackT UnpackAlphaLast(unsigned Color, bool Alpha = true)
    {
        UnpackT Result;
        if(Alpha)
        {
            Result.x = ((Color >> 24) & 0xFF) / 255.0f;
            Result.y = ((Color >> 16) & 0xFF) / 255.0f;
            Result.z = ((Color >> 8) & 0xFF) / 255.0f;
            Result.a = ((Color >> 0) & 0xFF) / 255.0f;
        }
        else
        {
            Result.x = ((Color >> 16) & 0xFF) / 255.0f;
            Result.y = ((Color >> 8) & 0xFF) / 255.0f;
            Result.z = ((Color >> 0) & 0xFF) / 255.0f;
            Result.a = 1.0f;
        }
        return Result;
    }
};
 
class ColorHSLA : public color4_base<ColorHSLA>
{
public:
    using color4_base::color4_base;
    constexpr ColorHSLA() = default;
 
    constexpr static const float DARKEST_LGT = 0.5f;
    constexpr static const float DARKEST_LGT7 = 61.0f / 255.0f;
 
    constexpr ColorHSLA UnclampLighting(float Darkest) const
    {
        ColorHSLA col = *this;
        col.l = Darkest + col.l * (1.0f - Darkest);
        return col;
    }
 
    constexpr unsigned Pack(bool Alpha = true) const
    {
        return color4_base::Pack(Alpha);
    }
 
    constexpr unsigned Pack(float Darkest, bool Alpha = false) const
    {
        ColorHSLA col = *this;
        col.l = (l - Darkest) / (1 - Darkest);
        col.l = std::clamp(col.l, 0.0f, 1.0f);
        return col.Pack(Alpha);
    }
};
 
class ColorHSVA : public color4_base<ColorHSVA>
{
public:
    using color4_base::color4_base;
    constexpr ColorHSVA() = default;
};
 
class ColorRGBA : public color4_base<ColorRGBA>
{
public:
    using color4_base::color4_base;
    constexpr ColorRGBA() = default;
 
    constexpr ColorRGBA Multiply(const ColorRGBA &Other) const
    {
        ColorRGBA Color = *this;
        Color.r *= Other.r;
        Color.g *= Other.g;
        Color.b *= Other.b;
        Color.a *= Other.a;
        return Color;
    }
 
    template<Numeric T>
    constexpr ColorRGBA Multiply(const T &Factor) const
    {
        ColorRGBA Color = *this;
        Color.r *= Factor;
        Color.g *= Factor;
        Color.b *= Factor;
        Color.a *= Factor;
        return Color;
    }
};
 
template<typename T, typename F>
constexpr T color_cast(const F &) = delete;
 
template<>
constexpr ColorHSLA color_cast(const ColorRGBA &rgb)
{
    float Min = std::min({rgb.r, rgb.g, rgb.b});
    float Max = std::max({rgb.r, rgb.g, rgb.b});
 
    float c = Max - Min;
    float h = RgbToHue(rgb.r, rgb.g, rgb.b);
    float l = 0.5f * (Max + Min);
    float s = (Max != 0.0f && Min != 1.0f) ? (c / (1 - (absolute(2 * l - 1)))) : 0;
 
    return ColorHSLA(h, s, l, rgb.a);
}
 
template<>
constexpr ColorRGBA color_cast(const ColorHSLA &hsl)
{
    float h1 = hsl.h * 6;
    float c = (1.f - absolute(2 * hsl.l - 1)) * hsl.s;
    float x = c * (1.f - absolute(std::fmod(h1, 2) - 1.f));
 
    float r = 0.0f;
    float g = 0.0f;
    float b = 0.0f;
    switch(round_truncate(h1))
    {
    case 0:
        r = c;
        g = x;
        break;
    case 1:
        r = x;
        g = c;
        break;
    case 2:
        g = c;
        b = x;
        break;
    case 3:
        g = x;
        b = c;
        break;
    case 4:
        r = x;
        b = c;
        break;
    case 5:
    case 6:
        r = c;
        b = x;
        break;
    }
 
    float m = hsl.l - (c / 2);
    return ColorRGBA(r + m, g + m, b + m, hsl.a);
}
 
template<>
constexpr ColorHSLA color_cast(const ColorHSVA &hsv)
{
    float l = hsv.v * (1 - hsv.s * 0.5f);
    return ColorHSLA(hsv.h, (l == 0.0f || l == 1.0f) ? 0 : (hsv.v - l) / std::min(l, 1 - l), l, hsv.a);
}
 
template<>
constexpr ColorHSVA color_cast(const ColorHSLA &hsl)
{
    float v = hsl.l + hsl.s * std::min(hsl.l, 1 - hsl.l);
    return ColorHSVA(hsl.h, v == 0.0f ? 0 : 2 - (2 * hsl.l / v), v, hsl.a);
}
 
template<>
constexpr ColorRGBA color_cast(const ColorHSVA &hsv)
{
    return color_cast<ColorRGBA>(color_cast<ColorHSLA>(hsv));
}
 
template<>
constexpr ColorHSVA color_cast(const ColorRGBA &rgb)
{
    return color_cast<ColorHSVA>(color_cast<ColorHSLA>(rgb));
}
 
template<typename T>
constexpr T color_scale(const T &col, float s)
{
    return T(col.x * s, col.y * s, col.z * s, col.a * s);
}
 
template<typename T>
constexpr T color_invert(const T &col)
{
    return T(1.0f - col.x, 1.0f - col.y, 1.0f - col.z, 1.0f - col.a);
}
 
template<typename T>
std::optional<T> color_parse(const char *pStr);
 
#endif