phase.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_PHYSICS_LIGHT_PHASE_HPP
#define ANTKEEPER_PHYSICS_LIGHT_PHASE_HPP
 
#include <engine/math/numbers.hpp>
#include <cmath>
 
namespace physics {
namespace light {
 
namespace phase {
 
template <class T>
T cornette_shanks(T mu, T g);
 
template <class T>
T henyey_greenstein(T mu, T g);
 
template <class T>
constexpr T isotropic()
{
    return T(1) / (T(4) * math::pi<T>);
}
 
template <class T>
T rayleigh(T mu);
 
template <class T>
T cornette_shanks(T mu, T g)
{
    static const T k = T(3) / (T(8) * math::pi<T>);
    const T gg = g * g;
    const T num = (T(1) - gg) * (T(1) + mu * mu);
    const T den = (T(2) + gg) * std::pow(T(1) + gg - T(2) * g * mu, T(1.5));
    return k * num / den;
}
 
template <class T>
T henyey_greenstein(T mu, T g)
{
    const T gg = g * g;
    return (T(1) - gg) / (T(4) * math::pi<T> * std::pow(T(1) + gg - T(2) * g * mu, T(1.5)));
}
 
template <class T>
T rayleigh(T mu)
{
    static const T k = T(3) / (T(16) * math::pi<T>);
    return k * (1.0 + mu * mu);
}
 
} // namespace phase
 
} // namespace light
} // namespace physics
 
#endif // ANTKEEPER_PHYSICS_LIGHT_PHASE_HPP