1 files changed, 7 insertions, 0 deletions
diff --git a/lib/vec3.rb b/lib/vec3.rb
index 3069b65..478fe4c 100644
--- a/lib/vec3.rb
+++ b/lib/vec3.rb
@@ -60,6 +60,13 @@ class Vec3
     self - normal * dot(normal) * 2
   end
 
+  def refract(normal, etaratio)
+    costheta = [(-self).dot(normal), 1.0].min
+    rout_perp = (self + normal * costheta) * etaratio
+    rout_parr = normal * -((1.0 - rout_perp.mag_sqr).abs ** 0.5)
+    rout_perp + rout_parr
+  end
+
   def in_unit_sphere?
     mag_sqr < 1
   end