From 1920376e342cc968e00fe2dadf375195fb82d605 Mon Sep 17 00:00:00 2001
From: djairoh <djairoh@mykolab.com>
Date: Thu, 16 Apr 2026 15:38:01 +0200
Subject: [PATCH] ft (wip): 10: dielectrics

---
 src/main.rs                         |  3 ++-
 src/objects/hit.rs                  | 10 ++++++++--
 src/objects/materials.rs            |  1 +
 src/objects/materials/dielectric.rs | 30 +++++++++++++++++++++++++++++
 src/objects/sphere.rs               | 12 ++++++++++--
 src/vec3.rs                         | 22 +++++++++++++++++++--
 6 files changed, 71 insertions(+), 7 deletions(-)
 create mode 100644 src/objects/materials/dielectric.rs

diff --git a/src/main.rs b/src/main.rs
index 12af2af..1b6d294 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -8,6 +8,7 @@ mod vec3;
 use std::sync::Arc;
 
 use crate::camera::Camera;
+use crate::objects::materials::dielectric::Dielectric;
 use crate::objects::materials::lambertian::{Lambertian, Metal};
 use crate::objects::sphere::Sphere;
 use crate::ray::Ray;
@@ -21,7 +22,7 @@ fn main() {
     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(Metal::rgb(0.8, 0.8, 0.8, 1., 0.3));
+    let left = Arc::new(Dielectric::new(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())];
diff --git a/src/objects/hit.rs b/src/objects/hit.rs
index 633510e..b1caaba 100644
--- a/src/objects/hit.rs
+++ b/src/objects/hit.rs
@@ -11,15 +11,17 @@ pub struct Hit {
     p: Vec3,
     n: Vec3,
     mat: Arc<dyn Material>,
+    front_face: bool,
 }
 
 impl Hit {
-    pub fn new(t: f32, p: Vec3, n: Vec3, mat: Arc<dyn Material>) -> Self {
+    pub fn new(t: f32, p: Vec3, n: Vec3, mat: Arc<dyn Material>, front_face: bool) -> Self {
         Self {
             t: t,
             p: p,
-            n: n,
+            n: if front_face { n } else { -n },
             mat: mat,
+            front_face: front_face,
         }
     }
 
@@ -39,6 +41,10 @@ impl Hit {
         self.mat.clone()
     }
 
+    pub fn front_face(&self) -> bool {
+        self.front_face
+    }
+
     pub fn hit_list<T: Hittable>(hittables: &Vec<T>, r: &Ray) -> Option<Hit> {
         let mut closest: Option<Hit> = None;
         for hittable in hittables {
diff --git a/src/objects/materials.rs b/src/objects/materials.rs
index 39a34e0..ba0b2cd 100644
--- a/src/objects/materials.rs
+++ b/src/objects/materials.rs
@@ -1,2 +1,3 @@
+pub mod dielectric;
 pub mod lambertian;
 pub mod traits;
diff --git a/src/objects/materials/dielectric.rs b/src/objects/materials/dielectric.rs
new file mode 100644
index 0000000..441b252
--- /dev/null
+++ b/src/objects/materials/dielectric.rs
@@ -0,0 +1,30 @@
+use crate::{
+    objects::{hit::Hit, materials::traits::Material},
+    ray::Ray,
+    vec3::Colour,
+};
+
+pub struct Dielectric {
+    refraction_index: f32,
+}
+
+impl Dielectric {
+    pub fn new(refraction_index: f32) -> Self {
+        Self {
+            refraction_index: refraction_index,
+        }
+    }
+}
+
+impl Material for Dielectric {
+    fn scatter(&self, hit: &Hit, ray: &Ray) -> Option<(Ray, Colour)> {
+        let ri = if hit.front_face() {
+            1. / self.refraction_index
+        } else {
+            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.)))
+    }
+}
diff --git a/src/objects/sphere.rs b/src/objects/sphere.rs
index 19bdbee..1a64a09 100644
--- a/src/objects/sphere.rs
+++ b/src/objects/sphere.rs
@@ -4,6 +4,7 @@ use std::sync::Arc;
 use crate::objects::hit::Hit;
 use crate::objects::materials::traits::Material;
 use crate::objects::traits::Hittable;
+use crate::ray::Ray;
 use crate::Vec3;
 
 pub struct Sphere {
@@ -31,7 +32,7 @@ impl Sphere {
 }
 
 impl Hittable for Sphere {
-    fn hit(&self, r: &crate::ray::Ray) -> Option<Hit> {
+    fn hit(&self, r: &Ray) -> Option<Hit> {
         let oc = self.center - r.origin();
         let a = r.dir().length_squared();
         let h = r.dir().dot(&oc);
@@ -43,7 +44,14 @@ impl Hittable for Sphere {
         } else {
             let t = (h - sqrt(d)) / a;
             let p = r.at(t);
-            Some(Hit::new(t, p, self.normal_at(&p), self.material.clone()))
+            let out_n = (p - self.center) / self.radius;
+            Some(Hit::new(
+                t,
+                p,
+                self.normal_at(&p),
+                self.material.clone(),
+                out_n.dot(r.dir()) < 0.,
+            ))
         }
     }
 
diff --git a/src/vec3.rs b/src/vec3.rs
index 6b355b9..0e35b8b 100644
--- a/src/vec3.rs
+++ b/src/vec3.rs
@@ -101,8 +101,18 @@ impl Vec3 {
             && default().is_close(self.b, 0.)
     }
 
-    pub fn reflect(&self, o: &Vec3) -> Vec3 {
-        *self - 2. * self.dot(o) * o
+    pub fn reflect(&self, n: &Self) -> Self {
+        *self - 2. * self.dot(n) * n
+    }
+
+    pub fn refract(&self, n: &Self, etai_over_etat: f32) -> Self {
+        let mut cos_theta = -self.dot(n);
+        cos_theta = if cos_theta > 1.0 { 1.0 } else { cos_theta };
+
+        let r_out_perp = etai_over_etat * (*self + cos_theta * n);
+        let r_out_parr = -sqrt((1. - r_out_perp.length_squared()).abs()) * n;
+
+        return r_out_perp + r_out_parr;
     }
 
     pub fn output(self) -> image::Rgb<u8> {
@@ -139,6 +149,14 @@ impl Vec3 {
     }
 }
 
+impl Neg for &Vec3 {
+    type Output = Vec3;
+
+    fn neg(self) -> Self::Output {
+        -*self
+    }
+}
+
 impl Neg for Vec3 {
     type Output = Self;