这一章实现了密度恒定的雾。
光线可以穿过雾,也可能会在雾的里面折射,这个折射点可以在雾里面的任何地方。
hit函数
bool constant_medium::hit(const ray& r, double t_min, double t_max, hit_record& rec) const {
// Print occasional samples when debugging. To enable, set enableDebug true.
const bool enableDebug = false;
const bool debugging = enableDebug && random_double() < 0.00001;
hit_record rec1, rec2;
if (!boundary->hit(r, -infinity, infinity, rec1))
return false;
if (!boundary->hit(r, rec1.t+0.0001, infinity, rec2))
return false;
if (debugging) std::cerr << "\nt_min=" << rec1.t << ", t_max=" << rec2.t << '\n';
if (rec1.t < t_min) rec1.t = t_min;
if (rec2.t > t_max) rec2.t = t_max;
if (rec1.t >= rec2.t)
return false;
if (rec1.t < 0)
rec1.t = 0;
const auto ray_length = r.direction().length();
const auto distance_inside_boundary = (rec2.t - rec1.t) * ray_length;
const auto hit_distance = neg_inv_density * log(random_double());
if (hit_distance > distance_inside_boundary)
return false;
rec.t = rec1.t + hit_distance / ray_length;
rec.p = r.at(rec.t);
if (debugging) {
std::cerr << "hit_distance = " << hit_distance << '\n'
<< "rec.t = " << rec.t << '\n'
<< "rec.p = " << rec.p << '\n';
}
rec.normal = vec3(1,0,0); // arbitrary
rec.front_face = true; // also arbitrary
rec.mat_ptr = phase_function;
return true;
}
先算出了光线和物体的两个交点,然后根据设定好的密度,随机取一段距离加到第一个光线和物体交点上,作为折射点。如果折射点在物体之外,说明光线穿了过去,反之说明光线发生了折射。
250spp才勉强能看,一个半小时,造孽啊