🎨 Add dialectric material

5 files changed, 99 insertions, 6 deletions

diff --git a/racer-tracer/src/main.rs b/racer-tracer/src/main.rs
index d95717d..5331fd1 100644
--- a/racer-tracer/src/main.rs
+++ b/racer-tracer/src/main.rs
@@ -16,7 +16,7 @@ use std::{
     vec::Vec,
 };
 
-use material::{lambertian::Lambertian, metal::Metal, Material};
+use material::{dialectric::Dialectric, lambertian::Lambertian, metal::Metal, Material};
 use minifb::{Key, Window, WindowOptions};
 use synchronoise::SignalEvent;
 
@@ -39,11 +39,11 @@ fn create_scene() -> Scene {
     let material_ground: SharedMaterial =
         Arc::new(Box::new(Lambertian::new(Color::new(0.8, 0.8, 0.0))));
     let material_center: SharedMaterial =
-        Arc::new(Box::new(Lambertian::new(Color::new(0.7, 0.3, 0.3))));
-    let material_left: SharedMaterial =
-        Arc::new(Box::new(Metal::new(Color::new(0.8, 0.8, 0.8), 0.3)));
+        Arc::new(Box::new(Lambertian::new(Color::new(0.1, 0.2, 0.5))));
+    let material_left: SharedMaterial = Arc::new(Box::new(Dialectric::new(1.5)));
+
     let material_right: SharedMaterial =
-        Arc::new(Box::new(Metal::new(Color::new(0.8, 0.6, 0.2), 0.1)));
+        Arc::new(Box::new(Metal::new(Color::new(0.8, 0.6, 0.2), 0.0)));
 
     scene.add(Box::new(Sphere::new(
         Vec3::new(0.0, -100.5, -1.0),
@@ -60,6 +60,13 @@ fn create_scene() -> Scene {
         0.5,
         Arc::clone(&material_left),
     )));
+
+    scene.add(Box::new(Sphere::new(
+        Vec3::new(-1.0, 0.0, -1.0),
+        -0.4,
+        Arc::clone(&material_left),
+    )));
+
     scene.add(Box::new(Sphere::new(
         Vec3::new(1.0, 0.0, -1.0),
         0.5,
diff --git a/racer-tracer/src/material.rs b/racer-tracer/src/material.rs
index b6ce418..a43b29f 100644
--- a/racer-tracer/src/material.rs
+++ b/racer-tracer/src/material.rs
@@ -1,3 +1,4 @@
+pub mod dialectric;
 pub mod lambertian;
 pub mod metal;
 
diff --git a/racer-tracer/src/material/dialectric.rs b/racer-tracer/src/material/dialectric.rs
new file mode 100644
index 0000000..5f3aa02
--- /dev/null
+++ b/racer-tracer/src/material/dialectric.rs
@@ -0,0 +1,53 @@
+use crate::{
+    material::Material,
+    ray::Ray,
+    util::random_double,
+    vec3::{dot, reflect, refract, Color},
+};
+
+pub struct Dialectric {
+    refraction_index: f64,
+}
+
+impl Dialectric {
+    pub fn new(refraction_index: f64) -> Self {
+        Self { refraction_index }
+    }
+
+    fn reflectance(cosine: f64, refraction_index: f64) -> f64 {
+        // Schlick approximation
+        let mut r0 = (1.0 - refraction_index) / (1.0 + refraction_index);
+        r0 = r0 * r0;
+        r0 + (1.0 - r0) * (1.0 - cosine).powf(5.0)
+    }
+}
+
+impl Material for Dialectric {
+    fn scatter(
+        &self,
+        ray: &crate::ray::Ray,
+        rec: &crate::geometry::HitRecord,
+    ) -> Option<(Ray, Color)> {
+        let refraction_ratio = if rec.front_face {
+            1.0 / self.refraction_index
+        } else {
+            self.refraction_index
+        };
+
+        let unit_direction = &ray.direction().unit_vector();
+        let cos_theta = f64::min(dot(&-unit_direction, &rec.normal), 1.0);
+        let sin_theta = f64::sqrt(1.0 - cos_theta * cos_theta);
+
+        let cannot_refract = refraction_ratio * sin_theta > 1.0;
+
+        let direction = if cannot_refract
+            || Dialectric::reflectance(cos_theta, refraction_ratio) > random_double()
+        {
+            reflect(unit_direction, &rec.normal)
+        } else {
+            refract(unit_direction, &rec.normal, refraction_ratio)
+        };
+
+        Some((Ray::new(rec.point, direction), Color::new(1.0, 1.0, 1.0)))
+    }
+}
diff --git a/racer-tracer/src/render.rs b/racer-tracer/src/render.rs
index 9d029e3..c5013cf 100644
--- a/racer-tracer/src/render.rs
+++ b/racer-tracer/src/render.rs
@@ -50,6 +50,10 @@ pub fn raytrace(
     scale: usize,
     max_depth: usize,
 ) {
+    // TODO: This scale shit doesn't work.
+    // Just force power of two or other solutions to avoid this.
+    // Can be ok for preview but the actual render could use a different function.
+
     let mut scaled_width = image.width / scale;
     let mut scaled_height = image.height / scale;
     // In the case where we get an odd one out we patch the widht and
@@ -66,7 +70,7 @@ pub fn raytrace(
         scaled_width += 1;
     }
 
-    if scaled_width * scale != image.height
+    if scaled_height * scale != image.height
         && (image.y + scaled_height * scale + 1 < image.screen_height)
     {
         scaled_height += 1;
diff --git a/racer-tracer/src/vec3.rs b/racer-tracer/src/vec3.rs
index 659d3ed..9061eba 100644
--- a/racer-tracer/src/vec3.rs
+++ b/racer-tracer/src/vec3.rs
@@ -146,6 +146,18 @@ impl ops::Add<Vec3> for Vec3 {
     }
 }
 
+impl ops::Add<Vec3> for &Vec3 {
+    type Output = Vec3;
+
+    fn add(self, rhs: Vec3) -> Self::Output {
+        Vec3::new(
+            self.data[0] + rhs.data[0],
+            self.data[1] + rhs.data[1],
+            self.data[2] + rhs.data[2],
+        )
+    }
+}
+
 impl ops::AddAssign<Vec3> for Vec3 {
     fn add_assign(&mut self, rhs: Vec3) {
         self.data[0] += rhs.data[0];
@@ -275,6 +287,14 @@ impl ops::Neg for Vec3 {
     }
 }
 
+impl ops::Neg for &Vec3 {
+    type Output = Vec3;
+
+    fn neg(self) -> Self::Output {
+        Vec3::new(-self.data[0], -self.data[1], -self.data[2])
+    }
+}
+
 impl PartialEq for Vec3 {
     fn eq(&self, other: &Self) -> bool {
         self.data[0] == other.data[0]
@@ -305,6 +325,14 @@ pub fn reflect(v1: &Vec3, v2: &Vec3) -> Vec3 {
     v1 - 2.0 * v1.dot(v2) * v2
 }
 
+pub fn refract(uv: &Vec3, n: &Vec3, etai_over_etat: f64) -> Vec3 {
+    let cos_theta = f64::min(dot(&-uv, n), 1.0);
+
+    let r_out_perp = etai_over_etat * (uv + (cos_theta * n));
+    let r_out_parallel = -f64::sqrt(f64::abs(1.0 - r_out_perp.length_squared())) * n;
+    r_out_perp + r_out_parallel
+}
+
 pub fn random_in_unit_sphere() -> Vec3 {
     let mut v = Vec3::random_range(-1.0, 1.0);
     while v.length_squared() >= 1.0 {