Add dielectric pbrt material

ray-tracing-pbrt-scene/src/material.rs

@@ -1,4 +1,6 @@
-use ray_tracing_core::{color::Color, material::SampleResult, prelude::*};
+use ray_tracing_core::{
+    color::Color, material::SampleResult, math::material::fresnel_real, prelude::*,
+};
 
 use crate::{
     either::Either,
@@ -103,20 +105,33 @@ impl<R: Rng> PbrtMaterial<R> for PbrtDielectricMaterial {
         let _ = rng;
         let _ = v;
         let _ = u;
-        let _ = match self.eta {
+        let eta = match self.eta {
             Either::A(Either::A(eta)) => eta,
             _ => todo!(),
         };
 
-        // let c = w_in.y();
-        // let w_out = -w_in * eta
-        //     + (eta * c - Float::sqrt(1.0 - eta * eta * (1.0 - c * c))) * Dir3::new(0.0, -1.0, 1.0);
+        let (n1, n2) = if w_in.y() >= 0.0 {
+            (1.0, eta)
+        } else {
+            (eta, 1.0)
+        };
 
-        SampleResult::new(
-            Dir3::new(0.0, 2.0 * w_in.y(), 0.0) - w_in,
-            Color::white(),
-            true,
-        )
+        let r = fresnel_real(w_in.y().abs(), n1, n2);
+
+        if r >= rng.r#gen() {
+            SampleResult::new(
+                Dir3::new(0.0, 2.0 * w_in.y(), 0.0) - w_in,
+                Color::white(),
+                true,
+            )
+        } else {
+            let r = n1 / n2;
+            let w_out = -w_in * r
+                + (r * w_in.y().abs() - Float::sqrt(1.0 - r * r * (1.0 - w_in.y() * w_in.y())))
+                    * Dir3::new(0.0, if w_in.y() > 0.0 { 1.0 } else { -1.0 }, 0.0);
+
+            SampleResult::new(w_out, Color::white(), true)
+        }
     }
 
     fn pdf(&self, u: Float, v: Float, w_in: Dir3, w_out: Dir3) -> Float {