1 files changed, 32 insertions, 5 deletions

diff --git a/src/material.rs b/src/material.rs
index a654f4d..833ef19 100644
--- a/src/material.rs
+++ b/src/material.rs
@@ -1,3 +1,4 @@
+use rand::Rng;
 use crate::calculus::calculus::{Ray, Vec3};
 use crate::common::Color;
 use crate::object::HitRecord;
@@ -5,7 +6,8 @@ use crate::object::HitRecord;
 #[derive(Clone)]
 pub enum MaterialType {
     Diffuse,
-    Metal(f32), // color fuzz
+    Metallic(f32), // fuzz
+    Transparent(f32), // refraction index
 }
 
 #[derive(Clone)]
@@ -17,9 +19,9 @@ pub struct Material {
 impl Material {
     pub fn new(albedo: Color, material_type: MaterialType) -> Self {
         let mut material_type = material_type;
-        if let MaterialType::Metal(fuzz) = material_type {
+        if let MaterialType::Metallic(fuzz) = material_type {
             let fuzz = if fuzz <  1.0 { fuzz } else { fuzz };
-            material_type = MaterialType::Metal(fuzz);
+            material_type = MaterialType::Metallic(fuzz);
         }
         Self { albedo, material_type }
     }
@@ -34,11 +36,30 @@ impl Material {
                     scatter_direction
                 }
             }
-            MaterialType::Metal(fuzz) => {
+            MaterialType::Metallic(fuzz) => {
                 let mut reflected = r_in.reflect(&rec.normal);
-                reflected.unit().add(&Vec3::random_unit().scalar_mul(fuzz))
+                reflected.add(&Vec3::random_unit().scalar_mul(fuzz))
 
             }
+            MaterialType::Transparent(refraction_index) => {
+                let ri = if rec.front_face {
+                    1.0 / refraction_index
+                } else {
+                    refraction_index
+                };
+                let cos_theta = f32::min(
+                    r_in.direction.unit().scalar_mul(-1.0).dot_prod(&rec.normal),
+                    1.0
+                );
+                let sin_theta = (1.0 - cos_theta * cos_theta).sqrt();
+                let cannot_refract = ri * sin_theta > 1.0;
+                let random: f32 = rand::rng().random();
+                if cannot_refract || Self::reflectance(cos_theta, ri) > random {
+                    r_in.direction.unit().reflect(&rec.normal)
+                } else {
+                    r_in.refract(&rec.normal, ri)
+                }
+            }
         };
         scattered.origin = rec.position;
         attenuation.r = self.albedo.r;
@@ -46,4 +67,10 @@ impl Material {
         attenuation.b = self.albedo.b;
         true
     }
+
+    fn reflectance(cosine: f32, refraction_index: f32) -> f32 {
+        let mut r0 = (1.0 - refraction_index) / (1.0 + refraction_index);
+        r0 = r0 * r0;
+        r0 + (1.0 - r0) * (1.0 - cosine).powi(5)
+    }
 }
\ No newline at end of file