💿🐜 Antkeeper source code
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98 lines
2.6 KiB
98 lines
2.6 KiB
/*
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* Copyright (C) 2021 Christopher J. Howard
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*
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* This file is part of Antkeeper source code.
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*
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* Antkeeper source code is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* Antkeeper source code is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with Antkeeper source code. If not, see <http://www.gnu.org/licenses/>.
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*/
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#ifndef ANTKEEPER_PHYSICS_LIGHT_PHASE_HPP
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#define ANTKEEPER_PHYSICS_LIGHT_PHASE_HPP
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#include "math/constants.hpp"
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#include <cmath>
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namespace physics {
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namespace light {
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/// Light-scattering phase functions.
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namespace phase {
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/**
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* Cornette-Shanks phase function.
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*
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* @param mu Cosine of the angle between the light and view directions.
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* @param g Asymmetry factor, on [-1, 1]. Positive values cause forward scattering, negative values cause back scattering.
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*/
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template <class T>
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T cornette_shanks(T mu, T g);
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/**
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* Henyey–Greenstein phase function.
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*
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* @param mu Cosine of the angle between the light and view directions.
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* @param g Asymmetry factor, on `[-1, 1]`. Positive values cause forward scattering, negative values cause back scattering.
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*
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* @see http://www.pbr-book.org/3ed-2018/Volume_Scattering/Phase_Functions.html
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*/
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template <class T>
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T henyey_greenstein(T mu, T g);
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/**
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* Isotropic phase function. Causes light to be scattered uniformly in all directions.
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*/
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template <class T>
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constexpr T isotropic()
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{
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return T(1) / (T(4) * math::pi<T>);
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}
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/**
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* Rayleigh phase function.
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*
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* @param mu Cosine of the angle between the light and view directions.
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*/
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template <class T>
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T rayleigh(T mu);
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template <class T>
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T cornette_shanks(T mu, T g)
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{
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static const T k = T(3) / (T(8) * math::pi<T>);
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const T gg = g * g;
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const T num = (T(1) - gg) * (T(1) + mu * mu);
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const T den = (T(2) + gg) * std::pow(T(1) + gg - T(2) * g * mu, T(1.5));
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return k * num / den;
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}
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template <class T>
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T henyey_greenstein(T mu, T g)
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{
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const T gg = g * g;
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return (T(1) - gg) / (T(4) * math::pi<T> * std::pow(T(1) + gg - T(2) * g * mu, T(1.5)));
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}
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template <class T>
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T rayleigh(T mu)
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{
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static const T k = T(3) / (T(16) * math::pi<T>);
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return k * (1.0 + mu * mu);
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}
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} // namespace phase
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} // namespace light
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} // namespace physics
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#endif // ANTKEEPER_PHYSICS_LIGHT_PHASE_HPP
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