implement beer's law for colourful dielectrics

2 files changed, 25 insertions, 1 deletions

diff --git a/src/material/dielectric.rs b/src/material/dielectric.rs
index bcacb78..1a49f73 100644
--- a/src/material/dielectric.rs
+++ b/src/material/dielectric.rs
@@ -1,10 +1,18 @@
+use std::ops::Neg;
+
 use super::Material;
 use crate::{hittable::HitRecord, vec3::Vec3};
 use crate::vec3::Color;
 use crate::ray::Ray;
 
+pub struct DielectricAttenuation {
+    pub albedo: Color,
+    pub constant: f64,
+}
+
 pub struct Dielectric {
     pub index_of_refraction: f64,
+    pub attenuation: Option<DielectricAttenuation>,
 }
 
 impl Dielectric {
@@ -18,7 +26,22 @@ impl Dielectric {
 
 impl Material for Dielectric {
     fn scatter(&self, ray_in: &Ray, hit_record: &HitRecord, attenuation: &mut Color, scattered: &mut Ray) -> bool {
-        *attenuation = Color { x: 1.0, y: 1.0, z: 1.0 };
+        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);
diff --git a/src/material/mod.rs b/src/material/mod.rs
index bf1eb24..c292ea1 100644
--- a/src/material/mod.rs
+++ b/src/material/mod.rs
@@ -4,6 +4,7 @@ mod metal;
 pub use metal::Metal;
 mod dielectric;
 pub use dielectric::Dielectric;
+pub use dielectric::DielectricAttenuation;
 mod diffuse_light;
 pub use diffuse_light::DiffuseLight;
 mod isotropic;