Shadows on bump-mapped surfaces in ray tracing

This paper presents a method of generating shadows on bump-mapped surfaces in ray tracing. The method yields images with realistic shadows influenced by bumpy surface geometry. In our method, intersections are calculated between eye/reflection/refraction rays and smooth original surfaces as usual, and the surfaces and shaded according to Blinn's bump mapping. For shadowing, however, we shift the intersection points based on the approximated bumpy surface shape, and the shadow rays are fired from the shifted intersection points. Since the method involves no explicit intersection calculation between rays and bumpy surfaces, it requires only a small amount of computation in addition to conventional ray tracting. It is easy to insert the method into existing ray tracers, and it can be applied to variants of ray tracing algorithms that use shadow rays.