From 2269bd102dbfcedea20504692977a15a6040393f Mon Sep 17 00:00:00 2001
From: hal8174 <henning.lindemann@pm.me>
Date: Thu, 28 Aug 2025 00:22:58 +0200
Subject: [PATCH] Add dielectric pbrt material

---
 ray-tracing-core/src/math/material.rs         | 15 ++++++++
 ray-tracing-core/src/math/mod.rs              |  1 +
 .../src/bin/fresnel.rs                        |  3 +-
 ray-tracing-material/src/microfacet.rs        | 16 +--------
 ray-tracing-pbrt-scene/src/material.rs        | 35 +++++++++++++------
 5 files changed, 43 insertions(+), 27 deletions(-)
 create mode 100644 ray-tracing-core/src/math/material.rs

diff --git a/ray-tracing-core/src/math/material.rs b/ray-tracing-core/src/math/material.rs
new file mode 100644
index 0000000..7300c7a
--- /dev/null
+++ b/ray-tracing-core/src/math/material.rs
@@ -0,0 +1,15 @@
+use crate::prelude::*;
+
+pub fn fresnel_real(cos_theta_in: Float, nu1: Float, nu2: Float) -> Float {
+    let nu_rel = nu1 / nu2;
+    let cos_theta_tr = Float::sqrt(1.0 - nu_rel * nu_rel * (1.0 - cos_theta_in * cos_theta_in));
+
+    let rs = ((nu1 * cos_theta_in - nu2 * cos_theta_tr)
+        / (nu1 * cos_theta_in + nu2 * cos_theta_tr))
+        .powi(2);
+    let rp = ((nu1 * cos_theta_tr - nu2 * cos_theta_in)
+        / (nu1 * cos_theta_tr + nu2 * cos_theta_in))
+        .powi(2);
+
+    0.5 * (rs + rp)
+}
diff --git a/ray-tracing-core/src/math/mod.rs b/ray-tracing-core/src/math/mod.rs
index be5acb3..8fa1126 100644
--- a/ray-tracing-core/src/math/mod.rs
+++ b/ray-tracing-core/src/math/mod.rs
@@ -1,6 +1,7 @@
 pub mod dir3;
 pub mod frame;
 pub mod mat3;
+pub mod material;
 pub mod pos3;
 pub mod sampling;
 
diff --git a/ray-tracing-material-visualizer/src/bin/fresnel.rs b/ray-tracing-material-visualizer/src/bin/fresnel.rs
index 90ae34c..2c32c52 100644
--- a/ray-tracing-material-visualizer/src/bin/fresnel.rs
+++ b/ray-tracing-material-visualizer/src/bin/fresnel.rs
@@ -1,6 +1,5 @@
 use plotters::prelude::*;
-use ray_tracing_core::prelude::*;
-use ray_tracing_material::microfacet::fresnel_real;
+use ray_tracing_core::{math::material::fresnel_real, prelude::*};
 
 fn main() -> Result<(), Box<dyn std::error::Error>> {
     let root = BitMapBackend::new("fresnel.png", (640, 480)).into_drawing_area();
diff --git a/ray-tracing-material/src/microfacet.rs b/ray-tracing-material/src/microfacet.rs
index 9f37681..afed1b0 100644
--- a/ray-tracing-material/src/microfacet.rs
+++ b/ray-tracing-material/src/microfacet.rs
@@ -1,5 +1,5 @@
 use rand_distr::{Distribution, Normal};
-use ray_tracing_core::{material::Material, prelude::*};
+use ray_tracing_core::{material::Material, math::material::fresnel_real, prelude::*};
 use std::fmt::Debug;
 
 #[derive(Debug)]
@@ -14,20 +14,6 @@ impl<D: MicrofacetDistribution + Debug> Microfacet<D> {
     }
 }
 
-pub fn fresnel_real(cos_theta_in: Float, nu1: Float, nu2: Float) -> Float {
-    let nu_rel = nu1 / nu2;
-    let cos_theta_tr = Float::sqrt(1.0 - nu_rel * nu_rel * (1.0 - cos_theta_in * cos_theta_in));
-
-    let rs = ((nu1 * cos_theta_in - nu2 * cos_theta_tr)
-        / (nu1 * cos_theta_in + nu2 * cos_theta_tr))
-        .powi(2);
-    let rp = ((nu1 * cos_theta_tr - nu2 * cos_theta_in)
-        / (nu1 * cos_theta_tr + nu2 * cos_theta_in))
-        .powi(2);
-
-    0.5 * (rs + rp)
-}
-
 impl<R: Rng, D: MicrofacetDistribution + Debug + Sync + Send> Material<R> for Microfacet<D> {
     fn eval(&self, w_in: Dir3, w_out: Dir3, _rng: &mut R) -> ray_tracing_core::prelude::Color {
         if w_out.y() > 0.0 && w_in.y() > 0.0 {
diff --git a/ray-tracing-pbrt-scene/src/material.rs b/ray-tracing-pbrt-scene/src/material.rs
index 4c837da..f9902fc 100644
--- a/ray-tracing-pbrt-scene/src/material.rs
+++ b/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 {