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//
// Created by Keuin on 2022/4/15.
//
#include "material_dielectric.h"
#include "tracelog.h"
bool material_dielectric::scatter(ray3d &r, const object &hit_obj, double hit_t, random_uv_gen_3d &ruvg) const {
const auto hit_p = r.at(hit_t);
assert(hit_obj.is_on(hit_p));
auto nv = hit_obj.normal_vector(hit_p);
const auto n1 = r.direction(); // incoming ray, unit vector
const bool outside = dot(nv, n1) < 0; // if the ray hits the outside of the surface
double rel_ri; // relative ri, source_ri/target_ri
if (!outside) {
nv = -nv; // use normal vector pointing to the inner
rel_ri = ri;
} else {
rel_ri = 1.0 / ri;
}
const auto cos_t1 = std::min(-dot(nv, n1), 1.0); // cos(theta1)
const auto sin_t1_s = 1 - cos_t1 * cos_t1; // sin(theta1)^2
const auto rel_ri_s = rel_ri * rel_ri;
const auto sin_t2_s = sin_t1_s * rel_ri_s;
double p_reflect; // probability of schlick reflection
bool reflect = false;
if (sin_t2_s > 1.0) {
TRACELOG(" reflect (TIR, ri=%f)\n", ri);
// sin(theta2)^2 > 1, no real solution
// TIR (total internal reflection)
reflect = true;
} else if ((p_reflect = reflectance(cos_t1, ri)) > ruvg.range01_scalar()) {
TRACELOG(" reflect (schlick, ri=%f, p=%f)\n", ri, p_reflect);
reflect = true;
}
if (reflect) {
r.direction(nv.reflect(n1));
r.source(hit_p);
return true;
} else {
// normal refract
TRACELOG(" refract (forced, ri=%f)\n", ri);
const auto sin_t2 = sqrt(sin_t2_s);
const auto cos_t2 = sqrt(1 - sin_t2_s);
const auto n2 = (-cos_t2 * nv) + (n1 + cos_t1 * nv).unit_vec() * sin_t2;
r.direction(n2);
r.source(hit_p);
return true;
}
}
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