2 files changed, 13 insertions, 1 deletions
diff --git a/src/scene/shapes/mod.rs b/src/scene/shapes/mod.rs
index 7fbb8db..9b6bdfd 100644
--- a/src/scene/shapes/mod.rs
+++ b/src/scene/shapes/mod.rs
@@ -2,9 +2,15 @@ mod sphere;
 
 pub use sphere::Sphere;
 
-use crate::core::Ray;
+use crate::core::{Vector3f, Ray};
 use crate::Float;
 
 pub trait Shape {
     fn intersect(&self, ray: &Ray) -> Option<Float>;
+
+    /// Calculates the normal at point
+    ///
+    /// Point is assumed to be on the circle.
+    /// The resulting vector is assumed to be normalized.
+    fn norm_at(&self, point: &Vector3f) -> Vector3f;
 }
diff --git a/src/scene/shapes/sphere.rs b/src/scene/shapes/sphere.rs
index e30c1ec..da7f321 100644
--- a/src/scene/shapes/sphere.rs
+++ b/src/scene/shapes/sphere.rs
@@ -35,6 +35,12 @@ impl Shape for Sphere {
         }
 
     }
+
+    fn norm_at(&self, point: &Vector3f) -> Vector3f {
+        let mut v = *point - self.center;
+        v /= self.radius;
+        v
+    }
 }
 
 #[cfg(test)]