From aeaf4994fe98c7ab49eab53c89f1ead1a013b92b Mon Sep 17 00:00:00 2001
From: Bill Thiede <git@xinu.tv>
Date: Fri, 5 Oct 2018 18:16:42 -0700
Subject: [PATCH] Implement isotropic scattering for ConstantMedium volumes.

---
 rtiow/src/constant_medium.rs      | 24 ++++++++++++++----------
 rtiow/src/material.rs             | 31 ++++++++++++++++++++++++++++++-
 rtiow/src/scenes/cornell_smoke.rs |  4 ++--
 3 files changed, 46 insertions(+), 13 deletions(-)

diff --git a/rtiow/src/constant_medium.rs b/rtiow/src/constant_medium.rs
index 5d5cb07..13b22a8 100644
--- a/rtiow/src/constant_medium.rs
+++ b/rtiow/src/constant_medium.rs
@@ -6,38 +6,42 @@ use rand::Rng;
 use aabb::AABB;
 use hitable::Hit;
 use hitable::HitRecord;
-use material::Material;
+use material::Isotropic;
 use ray::Ray;
+use texture::Texture;
 use vec3::Vec3;
 
-pub struct ConstantMedium<H, M>
+pub struct ConstantMedium<H, T>
 where
     H: Hit,
-    M: Material,
+    T: Texture,
 {
     density: f32,
-    material: M,
+    material: Isotropic<T>,
     hitable: H,
 }
 
-impl<H, M> ConstantMedium<H, M>
+impl<H, T> ConstantMedium<H, T>
 where
     H: Hit,
-    M: Material,
+    T: Texture,
 {
-    pub fn new(hitable: H, density: f32, material: M) -> ConstantMedium<H, M> {
+    pub fn new(hitable: H, density: f32, texture: T) -> ConstantMedium<H, T>
+    where
+        T: Texture,
+    {
         ConstantMedium {
             density,
-            material,
+            material: Isotropic::new(texture),
             hitable,
         }
     }
 }
 
-impl<H, M> Hit for ConstantMedium<H, M>
+impl<H, T> Hit for ConstantMedium<H, T>
 where
     H: Hit,
-    M: Material,
+    T: Texture,
 {
     fn hit(&self, r: Ray, t_min: f32, t_max: f32) -> Option<HitRecord> {
         let mut rng = rand::thread_rng();
diff --git a/rtiow/src/material.rs b/rtiow/src/material.rs
index 277b393..0a24ded 100644
--- a/rtiow/src/material.rs
+++ b/rtiow/src/material.rs
@@ -56,11 +56,40 @@ impl Material for Box<Material> {
     }
 }
 
+pub struct Isotropic<T>
+where
+    T: Texture,
+{
+    albedo: T,
+}
+
+impl<T> Isotropic<T>
+where
+    T: Texture,
+{
+    pub fn new(texture: T) -> Isotropic<T> {
+        Isotropic { albedo: texture }
+    }
+}
+
+impl<T> Material for Isotropic<T>
+where
+    T: Texture,
+{
+    fn scatter(&self, _r_in: &Ray, rec: &HitRecord) -> ScatterResponse {
+        let (u, v) = rec.uv;
+        ScatterResponse {
+            attenutation: self.albedo.value(u, v, rec.p),
+            scattered: Ray::new(rec.p, random_in_unit_sphere(), 0.),
+            reflected: true,
+        }
+    }
+}
+
 pub struct Lambertian<T>
 where
     T: Texture,
 {
-    // TODO(wathiede): implement texture sharing via references
     albedo: T,
 }
 
diff --git a/rtiow/src/scenes/cornell_smoke.rs b/rtiow/src/scenes/cornell_smoke.rs
index 6f5b05b..470ede0 100644
--- a/rtiow/src/scenes/cornell_smoke.rs
+++ b/rtiow/src/scenes/cornell_smoke.rs
@@ -59,7 +59,7 @@ pub fn new(opt: &Opt) -> Scene {
                 Vec3::new(130., 0., 65.),
             ),
             0.01,
-            Lambertian::new(ConstantTexture::new([1., 1., 1.])),
+            ConstantTexture::new([1., 1., 1.]),
         )),
         // Black smoke box on the left
         Box::new(ConstantMedium::new(
@@ -75,7 +75,7 @@ pub fn new(opt: &Opt) -> Scene {
                 Vec3::new(265., 0., 295.),
             ),
             0.01,
-            Lambertian::new(ConstantTexture::new([0., 0., 0.])),
+            ConstantTexture::new([0., 0., 0.]),
         )),
         // Green wall left
         Box::new(FlipNormals::new(YZRect::new(