Abstract : This paper describes an new and optimized direct ray tracing algorithm over complex implicit surfaces generated by skeletons. Its main originality is its ability to avoid unwanted blending between parts of the same object, thank to the portioning of the surface into several pieces, so called Implicit Patches. Moreover, these patches enable to exploit the properties of local field functions, and to speed-up considerably the rendering. Extensive statistics of the various optimizations proposed are given and discussed. The implantation into public domain software RayShade is sketched.