rustracer/src/material.rs

use rand::Rng;
use crate::hittable::HitRecord;
use crate::{Color, Ray, Vec3};

pub trait Scatterable {
    fn scatter(&self, ray: &Ray, hit_record: &HitRecord) -> Option<(Option<Ray>, Color)>;
}

#[derive(Debug, Clone)]
pub enum Material {
    Lambertian(Lambertian),
    Metal(Metal),
    Dielectric(Dielectric)
}

impl Default for Material {
    fn default() -> Self {
        Material::Lambertian(Lambertian::new(Color::default()))
    }
}

impl Scatterable for Material {
    fn scatter(&self, ray: &Ray, hit_record: &HitRecord) -> Option<(Option<Ray>, Color)> {
        match self {
            Material::Lambertian(l) => l.scatter(ray, hit_record),
            Material::Metal(m) => m.scatter(ray, hit_record),
            Material::Dielectric(d) => d.scatter(ray, hit_record)
        }
    }
}

#[derive(Debug, Clone)]
pub struct Lambertian {
    pub albedo: Color
}
impl Lambertian {
    pub fn new(albedo: Color) -> Self {
        Lambertian { albedo }
    }
}

impl Scatterable for Lambertian {
    fn scatter(&self, ray: &Ray, hit_record: &HitRecord) -> Option<(Option<Ray>, Color)> {
        let mut direction = hit_record.normal + Vec3::random_unit_vector();
        if direction.near_zero() {
            direction = hit_record.normal;
        }
        let scattered = Ray::new(hit_record.point, direction);
        Some((Some(scattered), self.albedo))
    }
}

#[derive(Debug, Clone)]
pub struct Metal {
    pub albedo: Color,
    pub fuzz: f64
}

impl Metal {
    pub fn new(albedo: Color, fuzz: f64) -> Self {
        Metal {
            albedo,
            fuzz: if fuzz < 1.0 { fuzz} else { 1.0 }
        }
    }
}

impl Scatterable for Metal {
    fn scatter(&self, ray: &Ray, hit_record: &HitRecord) -> Option<(Option<Ray>, Color)> {
        let reflected = ray.direction().unit_vector().reflected(&hit_record.normal);
        let scattered = Ray::new(
            hit_record.point,
            reflected + self.fuzz * Vec3::random_in_unit_sphere());
        if scattered.direction().dot(&hit_record.normal) > 0.0 {
            Some((Some(scattered), self.albedo))
        } else {
            None
        }
    }
}

#[derive(Debug, Clone)]
pub struct Dielectric { // Glass
    pub index_of_refraction: f64
}

impl Dielectric {
    pub fn new(index_of_refraction: f64) -> Self {
        Dielectric { index_of_refraction }
    }
    fn reflectance(cosine: f64, ref_idx: f64) -> f64 {
        let r0 = (1.0-ref_idx) / (1.0+ref_idx);
        let r0 = r0*r0;
        r0 + (1.0-r0)*((1.0-cosine).powi(5))
    }
}

impl Scatterable for Dielectric {
    fn scatter(&self, ray: &Ray, hit_record: &HitRecord) -> Option<(Option<Ray>, Color)> {
        let color = Color::new(1.0, 1.0, 1.0);
        let refraction_ratio = if hit_record.front_face {
            1.0/self.index_of_refraction
        } else {
            self.index_of_refraction
        };
        let unit_direction = ray.direction().unit_vector();
        let cos_theta = ((-unit_direction).dot(&hit_record.normal)).min(1.0);
        let sin_theta = (1.0 - cos_theta*cos_theta).sqrt();
        let cannot_refract = refraction_ratio * sin_theta > 1.0;
        let reflectance = Dielectric::reflectance(cos_theta, refraction_ratio);
        let mut rng = rand::thread_rng();

        if cannot_refract || reflectance > rng.gen::<f64>() {
            let reflected = unit_direction.reflected(&hit_record.normal);
            let reflected = Vec3::new(-reflected.x(), reflected.y(), -reflected.z());
            let scattered = Ray::new(hit_record.point, reflected);
            Some((Some(scattered), color))
        } else {
            let direction = unit_direction.refract_orig(&hit_record.normal, refraction_ratio);
            let scattered = Ray::new(hit_record.point, direction);
            Some((Some(scattered), color))
        }
    }
}