ray_triangle_intersect.hpp

/*
 * eos - A 3D Morphable Model fitting library written in modern C++11/14.
 *
 * File: include/eos/render/ray_triangle_intersect.hpp
 *
 * Copyright 2016-2019 Patrik Huber
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
#pragma once
 
#ifndef EOS_RAY_TRIANGLE_INTERSECT_HPP
#define EOS_RAY_TRIANGLE_INTERSECT_HPP
 
#include "eos/cpp17/optional.hpp"
 
#include "Eigen/Core"
 
#include <utility>
 
namespace eos {
namespace render {
 
inline std::pair<bool, cpp17::optional<float>>
ray_triangle_intersect(const Eigen::Vector3f& ray_origin, const Eigen::Vector3f& ray_direction,
                       const Eigen::Vector3f& v0, const Eigen::Vector3f& v1, const Eigen::Vector3f& v2,
                       bool enable_backculling)
{
    using Eigen::Vector3f;
    const float epsilon = 1e-6f;
 
    const Vector3f v0v1 = v1 - v0;
    const Vector3f v0v2 = v2 - v0;
 
    const Vector3f pvec = ray_direction.cross(v0v2);
 
    const float det = v0v1.dot(pvec);
 
    if (enable_backculling)
    {
        // If det is negative, the triangle is back-facing.
        // If det is close to 0, the ray misses the triangle.
        if (det < epsilon)
            return {false, cpp17::nullopt};
    } else
    {
        // If det is close to 0, the ray and triangle are parallel.
        if (std::abs(det) < epsilon)
            return {false, cpp17::nullopt};
    }
    const float inv_det = 1 / det;
 
    const Vector3f tvec = ray_origin - v0;
    const auto u = tvec.dot(pvec) * inv_det;
    if (u < 0 || u > 1)
        return {false, cpp17::nullopt};
 
    const Vector3f qvec = tvec.cross(v0v1);
    const auto v = ray_direction.dot(qvec) * inv_det;
    if (v < 0 || u + v > 1)
        return {false, cpp17::nullopt};
 
    const auto t = v0v2.dot(qvec) * inv_det;
 
    return {true, t};
};
 
} /* namespace render */
} /* namespace eos */
 
#endif /* EOS_RAY_TRIANGLE_INTERSECT_HPP */