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use std::ops::Neg;
use super::Material;
use crate::ray::Ray;
use crate::vec3::Color;
use crate::{hittable::HitRecord, vec3::Vec3};
pub struct DielectricAttenuation {
pub albedo: Color,
pub constant: f64,
}
pub struct Dielectric {
pub index_of_refraction: f64,
pub attenuation: Option<DielectricAttenuation>,
}
impl Dielectric {
fn reflectance(cosine: f64, ref_idx: f64) -> f64 {
// Using Schlick's Approximation:
let mut r0 = (1.0 - ref_idx) / (1.0 + ref_idx);
r0 *= r0;
r0 + (1.0 - r0) * (1.0 - cosine).powi(5)
}
}
impl Material for Dielectric {
fn scatter(
&self,
ray_in: &Ray,
hit_record: &HitRecord,
attenuation: &mut Color,
scattered: &mut Ray,
) -> bool {
if let Some(props) = &self.attenuation {
let outward_normal = if hit_record.front_face {
hit_record.normal.clone()
} else {
-&hit_record.normal
};
if outward_normal.dot(&ray_in.direction) > 0.0 {
let distance = (&ray_in.origin - &hit_record.p).length();
let falloff_ratio = (props.constant * distance).neg().exp();
*attenuation = &props.albedo * falloff_ratio;
} else {
*attenuation = props.albedo.clone();
}
} else {
*attenuation = Color {
x: 1.0,
y: 1.0,
z: 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_in.direction.unit_vector();
let cos_theta = hit_record.normal.dot(&-&unit_direction).min(1.0);
let sin_theta = (1.0 - cos_theta * cos_theta).sqrt();
let cannot_refract = refraction_ratio * sin_theta > 1.0;
let direction: Vec3;
if cannot_refract || Self::reflectance(cos_theta, refraction_ratio) > rand::random::<f64>()
{
direction = unit_direction.reflect(&hit_record.normal)
} else {
direction = unit_direction.refract(&hit_record.normal, refraction_ratio)
}
*scattered = Ray {
origin: hit_record.p.clone(),
direction,
time: ray_in.time,
};
true
}
}
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