material.h

#ifndef MATERIAL_H
#define MATERIAL_H
//==============================================================================================
// Originally written in 2016 by Peter Shirley <ptrshrl@gmail.com>
//
// To the extent possible under law, the author(s) have dedicated all copyright and related and
// neighboring rights to this software to the public domain worldwide. This software is
// distributed without any warranty.
//
// You should have received a copy (see file COPYING.txt) of the CC0 Public Domain Dedication
// along with this software. If not, see <http://creativecommons.org/publicdomain/zero/1.0/>.
//==============================================================================================

#include "rtweekend.h"

#include "hittable.h"
#include "texture.h"


class material {
  public:
    virtual ~material() = default;

    virtual color emitted(double u, double v, const point3& p) const {
        return color(0,0,0);
    }

    virtual bool scatter(
        const ray& r_in, const hit_record& rec, color& attenuation, ray& scattered
    ) const = 0;
};


class lambertian : public material {
  public:
    lambertian(const color& a) : albedo(make_shared<solid_color>(a)) {}
    lambertian(shared_ptr<texture> a) : albedo(a) {}

    bool scatter(const ray& r_in, const hit_record& rec, color& attenuation, ray& scattered)
    const override {
        auto scatter_direction = rec.normal + random_unit_vector();

        if (scatter_direction.near_zero())
            scatter_direction = rec.normal;

        scattered = ray(rec.p, scatter_direction, r_in.time());
        attenuation = albedo->value(rec.u, rec.v, rec.p);
        return true;
    }

  private:
    shared_ptr<texture> albedo;
};


class metal : public material {
  public:
    metal(const color& a, double f) : albedo(a), fuzz(f < 1 ? f : 1) {}

    bool scatter(const ray& r_in, const hit_record& rec, color& attenuation, ray& scattered)
    const override {
        vec3 reflected = reflect(unit_vector(r_in.direction()), rec.normal);
        scattered = ray(rec.p, reflected + fuzz*random_in_unit_sphere(), r_in.time());
        attenuation = albedo;
        return (dot(scattered.direction(), rec.normal) > 0);
    }

  private:
    color albedo;
    double fuzz;
};


class dielectric : public material {
  public:
    dielectric(double index_of_refraction) : ir(index_of_refraction) {}

    bool scatter(const ray& r_in, const hit_record& rec, color& attenuation, ray& scattered)
    const override {
        attenuation = color(1.0, 1.0, 1.0);
        double refraction_ratio = rec.front_face ? (1.0/ir) : ir;

        vec3 unit_direction = unit_vector(r_in.direction());
        double cos_theta = fmin(dot(-unit_direction, rec.normal), 1.0);
        double sin_theta = sqrt(1.0 - cos_theta*cos_theta);

        bool cannot_refract = refraction_ratio * sin_theta > 1.0;
        vec3 direction;

        if (cannot_refract || reflectance(cos_theta, refraction_ratio) > random_double())
            direction = reflect(unit_direction, rec.normal);
        else
            direction = refract(unit_direction, rec.normal, refraction_ratio);

        scattered = ray(rec.p, direction, r_in.time());
        return true;
    }

  private:
    double ir;

    static double reflectance(double cosine, double ref_idx) {

        auto r0 = (1-ref_idx) / (1+ref_idx);
        r0 = r0*r0;
        return r0 + (1-r0)*pow((1 - cosine),5);
    }
};


class diffuse_light : public material {
  public:
    diffuse_light(shared_ptr<texture> a) : emit(a) {}
    diffuse_light(const color& c) : emit(make_shared<solid_color>(c)) {}

    bool scatter(const ray& r_in, const hit_record& rec, color& attenuation, ray& scattered)
    const override {
        return false;
    }

    color emitted(double u, double v, const point3& p) const override {
        return emit->value(u, v, p);
    }

  private:
    shared_ptr<texture> emit;
};


class isotropic : public material {
  public:
    isotropic(const color& c) : albedo(make_shared<solid_color>(c)) {}
    isotropic(shared_ptr<texture> a) : albedo(a) {}

    bool scatter(const ray& r_in, const hit_record& rec, color& attenuation, ray& scattered)
    const override {
        scattered = ray(rec.p, random_unit_vector(), r_in.time());
        attenuation = albedo->value(rec.u, rec.v, rec.p);
        return true;
    }

  private:
    shared_ptr<texture> albedo;
};


#endif