xyz.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_XYZ_HPP
#define ANTKEEPER_COLOR_XYZ_HPP
 
#include <engine/math/vector.hpp>
 
namespace color {
 
 
template <class T>
[[nodiscard]] inline constexpr T xyz_to_luminance(const math::vec3<T>& x) noexcept
{
    return x[1];
}
 
template <class T>
[[nodiscard]] constexpr math::vec3<T> xyz_to_xyy(const math::vec3<T>& x) noexcept
{
    const T sum = x[0] + x[1] + x[2];
    return math::vec3<T>{x[0] / sum, x[1] / sum, x[1]};
}
 
template <class T>
[[nodiscard]] T xyz_match_x(T lambda)
{
    const T t0 = (lambda - T{442.0}) * ((lambda < T{442.0}) ? T{0.0624} : T{0.0374});
    const T t1 = (lambda - T{599.8}) * ((lambda < T{599.8}) ? T{0.0264} : T{0.0323});
    const T t2 = (lambda - T{501.1}) * ((lambda < T{501.1}) ? T{0.0490} : T{0.0382});
    
    const T x0 = T{ 0.362} * std::exp(T{-0.5} * t0 * t0);
    const T x1 = T{ 1.056} * std::exp(T{-0.5} * t1 * t1);
    const T x2 = T{-0.065} * std::exp(T{-0.5} * t2 * t2);
    
    return x0 + x1 + x2;
}
 
template <class T>
[[nodiscard]] T xyz_match_y(T lambda)
{
    const T t0 = (lambda - T{568.8}) * ((lambda < T{568.8}) ? T{0.0213} : T{0.0247});
    const T t1 = (lambda - T{530.9}) * ((lambda < T{530.9}) ? T{0.0613} : T{0.0322});
    
    const T y0 = T{0.821} * std::exp(T{-0.5} * t0 * t0);
    const T y1 = T{0.286} * std::exp(T{-0.5} * t1 * t1);
    
    return y0 + y1;
}
 
template <class T>
[[nodiscard]] T xyz_match_z(T lambda)
{
    const T t0 = (lambda - T{437.0}) * ((lambda < T{437.0}) ? T{0.0845} : T{0.0278});
    const T t1 = (lambda - T{459.0}) * ((lambda < T{459.0}) ? T{0.0385} : T{0.0725});
    
    const T z0 = T{1.217} * std::exp(T{-0.5} * t0 * t0);
    const T z1 = T{0.681} * std::exp(T{-0.5} * t1 * t1);
    
    return z0 + z1;
}
 
template <class T>
[[nodiscard]] math::vec3<T> xyz_match(T lambda)
{
    return math::vec3<T>
    {
        xyz_match_x<T>(lambda),
        xyz_match_y<T>(lambda),
        xyz_match_z<T>(lambda)
    };
}
 
 
} // namespace color
 
#endif // ANTKEEPER_COLOR_XYZ_HPP