rgb.hpp

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/*
 * Copyright (C) 2023  Christopher J. Howard
 *
 * This file is part of Antkeeper source code.
 *
 * Antkeeper source code is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Antkeeper source code is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Antkeeper source code.  If not, see <http://www.gnu.org/licenses/>.
 */
 
#ifndef ANTKEEPER_COLOR_RGB_HPP
#define ANTKEEPER_COLOR_RGB_HPP
 
#include <engine/color/cat.hpp>
#include <engine/math/matrix.hpp>
#include <engine/math/vector.hpp>
 
namespace color {
 
 
template <class T>
[[nodiscard]] constexpr math::mat3<T> rgb_to_xyz(const math::vec2<T>& r, const math::vec2<T>& g, const math::vec2<T>& b, const math::vec2<T>& w)
{
    const math::mat3<T> m = 
    {
        r[0], r[1], T{1} - r[0] - r[1],
        g[0], g[1], T{1} - g[0] - g[1],
        b[0], b[1], T{1} - b[0] - b[1]
    };
    
    const math::vec3<T> scale = math::inverse(m) * math::vec3<T>{w[0] / w[1], T{1}, (T{1} - w[0] - w[1]) / w[1]};
    
    return math::mat3<T>
    {
        m[0][0] * scale[0], m[0][1] * scale[0], m[0][2] * scale[0],
        m[1][0] * scale[1], m[1][1] * scale[1], m[1][2] * scale[1],
        m[2][0] * scale[2], m[2][1] * scale[2], m[2][2] * scale[2],
    };
}
 
template <class T>
struct rgb_color_space
{
    using transfer_function_type = math::vec3<T> (*)(const math::vec3<T>&);
    
    const math::vec2<T> r;
    
    const math::vec2<T> g;
    
    const math::vec2<T> b;
    
    const math::vec2<T> w;
    
    const transfer_function_type eotf;
    
    const transfer_function_type oetf;
    
    const math::mat3<T> to_xyz;
    
    const math::mat3<T> from_xyz;
    
    const math::vec3<T> to_y;
    
    constexpr rgb_color_space(const math::vec2<T>& r, const math::vec2<T>& g, const math::vec2<T>& b, const math::vec2<T>& w, transfer_function_type eotf, transfer_function_type oetf):
        r(r),
        g(g),
        b(b),
        w(w),
        eotf(eotf),
        oetf(oetf),
        to_xyz(rgb_to_xyz<T>(r, g, b, w)),
        from_xyz(math::inverse(to_xyz)),
        to_y{to_xyz[0][1], to_xyz[1][1], to_xyz[2][1]}
    {}
    
    [[nodiscard]] inline constexpr T luminance(const math::vec3<T>& x) const noexcept
    {
        return math::dot(x, to_y);
    }
};
 
template <class T>
[[nodiscard]] constexpr math::mat3<T> rgb_to_rgb(const rgb_color_space<T>& s0, const rgb_color_space<T>& s1, const math::mat3<T>& cone_response = bradford_cone_response<T>)
{
    return s1.from_xyz * cat_matrix(s0.w, s1.w, cone_response) * s0.to_xyz;
}
 
 
} // namespace color
 
#endif // ANTKEEPER_COLOR_RGB_HPP