From 03e5a88f9b7da79749370685e8f5afaf03a25b4a Mon Sep 17 00:00:00 2001
From: Sakarias Johansson <sakarias.johansson@goodbyekansas.com>
Date: Mon, 16 Jan 2023 20:58:55 +0100
Subject: =?UTF-8?q?=F0=9F=8E=A8=20Add=20dialectric=20material?=
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---
 racer-tracer/src/material/dialectric.rs | 53 +++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)
 create mode 100644 racer-tracer/src/material/dialectric.rs

(limited to 'racer-tracer/src/material')

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)))
+    }
+}
-- 
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