Realtime Shading of Folded Surfaces

In this paper we present a new, simple, and efficient way to illuminate folded surfaces with extended light sources in realtime including shadows. In a preprocessing step we compute the parts of the surrounding environment that are visible from a set of points on the surface and represent this information in a binary visibility map. The illumination of the scene, i.e., incoming light from different directions, is encoded in an environment map. This way, extended light sources and complex illumination conditions of the surface can be simulated. The binary visibility information stored in the visibility maps is used during runtime to calculate the incoming and outgoing radiance in the direction of the viewer for each sample point. Various reflection models like the Phong or Lafortune model can be incorporated into these calculations. After computing the radiance values in each sample point, the surface is shaded using simple Gouraud interpolation. Using the pre-computed visibility information, the whole shading and even the change of lighting conditions can be simulated in realtime by modifying the environment map. As an extension to the environment map we support additional point light sources whose parameters and positions can also be manipulated in realtime. Several examples of mesh illumination and shading are demonstrated. keywords: folded surfaces, cloth shading, shadowing, illumination