1 files changed, 20 insertions, 1 deletions
diff --git a/src/calculus.rs b/src/calculus.rs
index 568eb60..2e8a1d5 100644
--- a/src/calculus.rs
+++ b/src/calculus.rs
@@ -119,6 +119,19 @@ pub mod calculus {
                 )
             )
         }
+
+        pub fn refract(&self, normal: &Self, etai_over_etat: f32) -> Self {
+            let cos_theta = f32::min(
+                1.0,
+                self.scalar_mul(-1.0).dot_prod(&normal)
+            );
+            let r_out_perp = self
+                .add(&normal.scalar_mul(cos_theta))
+                .scalar_mul(etai_over_etat);
+            let f = (1.0 - r_out_perp.mag_sqr()).abs().sqrt();
+            let r_out_parallel = normal.scalar_mul(-1.0 * f);
+            r_out_perp.add(&r_out_parallel)
+        }
     }
 
     pub struct Ray {
@@ -133,7 +146,13 @@ pub mod calculus {
         }
 
         pub fn reflect(&self, normal: &Vec3) -> Vec3 {
-            self.direction.reflect(&normal)
+            // return unit direction vector
+            self.direction.reflect(&normal).unit()
+        }
+
+        pub fn refract(&self, normal: &Vec3, etai_over_etat: f32) -> Vec3 {
+            // return unit direction vector
+            self.direction.unit().refract(&normal, etai_over_etat)
         }
     }