5 files changed, 34 insertions, 13 deletions
diff --git a/src/core/ray.rs b/src/core/ray.rs
index 0517e50..19d3cf1 100644
--- a/src/core/ray.rs
+++ b/src/core/ray.rs
@@ -2,8 +2,12 @@
 use crate::core::Vector3f;
 use crate::Float;
 
+/// A ray that is sent into the world.
+/// This is the main type used for testing intersections.
 pub struct Ray {
+    /// Origin of the ray
     pub origin: Vector3f,
+    /// Direction is assumed to be a unit vector.
     pub direction: Vector3f,
 }
 
@@ -23,6 +27,7 @@ impl Ray {
         }
     }
 
+    /// Resolve a point on the ray at time t
     pub fn at(&self, t: Float) -> Vector3f {
         self.origin + self.direction * t
     }
diff --git a/src/core/spectrum.rs b/src/core/spectrum.rs
index bea056e..ed3505b 100644
--- a/src/core/spectrum.rs
+++ b/src/core/spectrum.rs
@@ -12,6 +12,7 @@ pub struct Spectrum {
 
 impl Spectrum {
     pub const ZERO: Self = Spectrum { c: [0.0; 3] };
+    pub const WHITE: Self = Spectrum { c: [1.0; 3] };
 
     pub fn new_rgb(r: Float, g: Float, b: Float) -> Spectrum {
         Spectrum { c: [r, g, b] }
diff --git a/src/world/hittable.rs b/src/world/hittable.rs
index c5a353e..e11a3bc 100644
--- a/src/world/hittable.rs
+++ b/src/world/hittable.rs
@@ -7,16 +7,26 @@ pub struct Intersection<'a> {
     /// Normal vector at intersection
     pub n: Vector3f,
     pub p: Vector3f,
+    pub front: bool,
     pub t: Float,
     pub m: Option<&'a dyn Material>,
 }
 
-impl Intersection<'_> {
-    pub fn norm_against_ray(&self, r: &Ray) -> Vector3f {
-        if self.n.dot(&r.direction) < 0.0 {
-            self.n
-        } else {
-            -self.n
+impl<'a> Intersection<'a> {
+    pub fn new(out_normal: Vector3f, point: Vector3f, ray: &Ray, t: Float) -> Self {
+        let front = ray.direction.dot(&out_normal) < 0.0;
+        Intersection {
+            n: { if front { out_normal } else { -out_normal } },
+            front,
+            p: point,
+            m: None,
+            t,
+        }
+    }
+
+    pub fn add_material_if_none(&mut self, mat: &'a dyn Material) {
+        if let None = self.m {
+            self.m = Some(mat);
         }
     }
 }
diff --git a/src/world/mod.rs b/src/world/mod.rs
index 53d8ad3..3a09522 100644
--- a/src/world/mod.rs
+++ b/src/world/mod.rs
@@ -27,7 +27,12 @@ impl Object {
 
 impl Hittable for Object {
     fn intersect(&self, ray: &Ray) -> Option<Intersection> {
-        self.shape.intersect(ray).map(|mut i| {i.m = Some(self.mat.as_ref()); i})
+        if let Some(mut inter) = self.shape.intersect(ray) {
+            inter.add_material_if_none(self.mat.as_ref());
+           Some(inter)
+        } else {
+            None
+        }
     }
 
     fn bounding_box(&self) -> Bound3f {
diff --git a/src/world/shapes/sphere.rs b/src/world/shapes/sphere.rs
index e3348de..9ecedd6 100644
--- a/src/world/shapes/sphere.rs
+++ b/src/world/shapes/sphere.rs
@@ -42,12 +42,12 @@ impl Hittable for Sphere {
                 return None
             }
             let w = ray.at(distance);
-            Some(Intersection {
-                n: self.norm_at(&w),
-                p: w,
-                t: distance,
-                m: None,
-            })
+            Some(Intersection::new(
+                    self.norm_at(&w),
+                    w,
+                    ray,
+                    distance,
+                    ))
         }
 
     }