Add Oren-Nayar and fix bugs

ray-tracing-material/src/microfacet.rs

@@ -2,34 +2,57 @@ use ray_tracing_core::{material::Material, prelude::*};
 use std::fmt::Debug;
 
 #[derive(Debug)]
-struct Microfacet<D: MicrofacetDistribution + Debug> {
+pub struct Microfacet<D: MicrofacetDistribution + Debug> {
     dist: D,
     color: Color,
 }
 
-fn fresnel(w_in: Dir3, n: Dir3, nu_rel: Float) -> Float {
-    todo!()
-}
-
-impl<R: Rng, D: MicrofacetDistribution + Debug + Sync> Material<R> for Microfacet<D> {
-    fn eval(
-        &self,
-        w_in: ray_tracing_core::prelude::Dir3,
-        w_out: ray_tracing_core::prelude::Dir3,
-        _rng: &mut R,
-    ) -> ray_tracing_core::prelude::Color {
-        let w_h = (w_in + w_out).normalize();
-
-        let g = self.dist.g1(w_in, w_h) * self.dist.g1(w_out, w_h);
-
-        self.color * fresnel(w_in, w_h, 1.0) * g * self.dist.d(w_h) / (4.0 * w_in.y() * w_out.y())
+impl<D: MicrofacetDistribution + Debug> Microfacet<D> {
+    pub fn new(dist: D, color: Color) -> Self {
+        Self { dist, color }
     }
 }
 
-struct BeckmannDistribution {
+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> 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 {
+            let w_h = (w_in + w_out).normalize();
+
+            let g = self.dist.g1(w_in, w_h) * self.dist.g1(w_out, w_h);
+
+            self.color * fresnel_real(Dir3::dot(w_in, w_h), 1.0, 1.3) * g * self.dist.d(w_h)
+                / (4.0 * w_in.y() * w_out.y()).max(0.0)
+        } else {
+            Color::black()
+        }
+    }
+}
+
+#[derive(Debug)]
+pub struct BeckmannDistribution {
     alpha: Float,
 }
 
+impl BeckmannDistribution {
+    pub fn new(alpha: Float) -> Self {
+        Self { alpha }
+    }
+}
+
 impl MicrofacetDistribution for BeckmannDistribution {
     fn g1(&self, w: Dir3, w_h: Dir3) -> Float {
         if w.y() > 0.0 && Dir3::dot(w, w_h) > 0.0 {
@@ -55,7 +78,7 @@ impl MicrofacetDistribution for BeckmannDistribution {
     }
 }
 
-trait MicrofacetDistribution {
+pub trait MicrofacetDistribution {
     fn g1(&self, w: Dir3, w_h: Dir3) -> Float;
 
     fn d(&self, w_h: Dir3) -> Float;