toytracer/material.cpp

#include "material.h"

#include <cmath>

bool Lambertian::scatter(const Ray& r_in, const hit_record& rec, Color& attenuation, Ray& scattered) const {
  //Vec3 scatter_direction = rec.normal + random_in_unit_sphere();
  Vec3 scatter_direction = rec.normal + random_unit_vector();
  //Vec3 scatter_direction = random_in_hemisphere(rec.normal);
  scattered = Ray(rec.p, scatter_direction);
  attenuation = albedo;
  return true;
}

bool Metal::scatter(const Ray& r_in, const hit_record& rec, Color& attenuation, Ray& scattered) const {
  Vec3 reflected = reflect(unit_vector(r_in.direction()), rec.normal);
  scattered = Ray(rec.p, reflected + fuzz * random_in_unit_sphere());
  attenuation = albedo;
  return (dot(scattered.direction(), rec.normal) > 0);
}

double schlick(double cosine, double ref_idx) {
  auto r0 = (1 - ref_idx) / (1 + ref_idx);
  r0 = r0 * r0;
  return r0 + (1 - r0) * std::pow((1 - cosine), 5);
}

bool Dielectric::scatter(const Ray& r_in, const hit_record& rec, Color& attenuation, Ray& scattered) const {
    attenuation = Color(1.0, 1.0, 1.0);
    double etai_over_etat = rec.front_face ? 1.0 / ref_idx : ref_idx;

    Vec3 unit_direction = unit_vector(r_in.direction());
    double cos_theta = std::fmin(dot(-unit_direction, rec.normal), 1.0);
    double sin_theta = std::sqrt(1.0 - cos_theta*cos_theta);
    double reflect_prob = schlick(cos_theta, etai_over_etat);
    if (etai_over_etat * sin_theta > 1.0 || random_double() < reflect_prob) {
        Vec3 reflected = reflect(unit_direction, rec.normal);
        scattered = Ray(rec.p, reflected);
        return true;
    }

    Vec3 refracted = refract(unit_direction, rec.normal, etai_over_etat);
    scattered = Ray(rec.p, refracted);
    return true;
}