From 79e6d04e504d70542684999dc035907e523f9de6 Mon Sep 17 00:00:00 2001
From: djairoh <djairoh@mykolab.com>
Date: Tue, 21 Apr 2026 23:03:46 +0200
Subject: [PATCH] ft: 11: dielectrics

---
 src/main.rs                         |  6 +++++-
 src/objects/materials/dielectric.rs | 31 ++++++++++++++++++++++++++---
 2 files changed, 33 insertions(+), 4 deletions(-)

diff --git a/src/main.rs b/src/main.rs
index 56ba16e..908463e 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -21,18 +21,22 @@ fn main() {
     pretty_env_logger::init();
 
     // setup objects
+    let blue = Arc::new(Metal::rgb(0.2, 0.4, 0.8, 1., 0.1));
     let metal = Arc::new(Metal::rgb(0.7, 0.4, 0.2, 1., 0.1));
     let ground = Arc::new(Lambertian::rgb(0.8, 0.8, 0., 1.0));
     let center = Arc::new(Lambertian::rgb(0.1, 0.2, 0.5, 1.));
     let left = Arc::new(Dielectric::new(1.5));
+    let bubble = Arc::new(Dielectric::new(1. / 1.5));
     let right = Arc::new(Metal::rgb(0.8, 0.6, 0.2, 1., 1.0));
 
     let mut world = vec![Sphere::xyz(0., 0.5, -0.8, 0.1, metal.clone())];
     world.push(Sphere::xyz(0., -100.5, -1., 100., ground.clone()));
     world.push(Sphere::xyz(0., 0., -1.2, 0.5, center.clone()));
     world.push(Sphere::xyz(-1., 0., -1.0, 0.5, left.clone()));
+    world.push(Sphere::xyz(-1., 0., -1.0, 0.4, bubble.clone()));
     world.push(Sphere::xyz(1., 0., -1.0, 0.5, right.clone()));
+    world.push(Sphere::xyz(0., 0.7, -0.4, 0.2, blue.clone()));
 
-    let c = Camera::new(16. / 9., 800, 2, 50);
+    let c = Camera::new(16. / 9., 1920, 3, 50);
     c.render(&world);
 }
diff --git a/src/objects/materials/dielectric.rs b/src/objects/materials/dielectric.rs
index 441b252..dfb8fd1 100644
--- a/src/objects/materials/dielectric.rs
+++ b/src/objects/materials/dielectric.rs
@@ -1,7 +1,11 @@
+use core::f32::math::sqrt;
+
+use rand::RngExt;
+
 use crate::{
     objects::{hit::Hit, materials::traits::Material},
     ray::Ray,
-    vec3::Colour,
+    vec3::{Colour, Vec3},
 };
 
 pub struct Dielectric {
@@ -14,6 +18,13 @@ impl Dielectric {
             refraction_index: refraction_index,
         }
     }
+
+    fn _reflectance(cos: f32, refraction_index: f32) -> f32 {
+        // Shlick's approximation
+        let mut r0 = (1. - refraction_index) / (1. + refraction_index);
+        r0 *= r0;
+        return r0 + (1. - r0) * (1. - cos).powf(5.);
+    }
 }
 
 impl Material for Dielectric {
@@ -24,7 +35,21 @@ impl Material for Dielectric {
             self.refraction_index
         };
         let unit = ray.dir().get_unit();
-        let refr = unit.refract(hit.n(), ri);
-        Some((Ray::new(*hit.p(), refr), Colour::new(1., 1., 1.)))
+        let cos_theta = if -unit.dot(hit.n()) > 1. {
+            1.
+        } else {
+            -unit.dot(hit.n())
+        };
+        let sin_theta = sqrt(1. - cos_theta * cos_theta);
+        let cannot_refract = ri * sin_theta > 1.;
+
+        let dir: Vec3;
+        let mut rng = rand::rng();
+        if cannot_refract || Dielectric::_reflectance(cos_theta, ri) > rng.random::<f32>() {
+            dir = unit.reflect(hit.n());
+        } else {
+            dir = unit.refract(hit.n(), ri);
+        }
+        Some((Ray::new(*hit.p(), dir), Colour::new(1., 1., 1.)))
     }
 }