The Ray Tracer Challenge

Normal Perturbation

Hark back to ​Smooth Triangles​, when you made triangles appear curved by modifying the normal that was reported to the renderer. It turns out that this technique can be used in a variety of ways, basically “lying” to the renderer so that the surface shading is done with modified normals. Check out the image, showing this technique applied to spheres and a plane.

By attaching a function to the shape (perhaps directly, or maybe via the material), you can have your normal_at function call the attached function to perturb, or add a small vector to, the normal at the given point. In the preceding image, the red sphere uses a sine ...