Visibility layers and their applications to rendering

Abstract

It is one of the greatest challenges to improve rendering efficiency. An important issue in rendering is to develop a geometric data structure which provides efficient visibility operations, because the most of the rendering time is spent for performing them. In this thesis, we present new data structures, called {\it visibility layers},to efficiently handle the visibility operations originated from a given area light source. Our structures maintain scene polygons in a sequence of layers according to their visibility from the source. The polygons in a layer do not obscure each other with respect to the source. From this property, a balanced 3D BSP tree can be constructed to accelerate visibility queries for the layer. Moreover, the shadow volumes cast by the polygons in the layer can be efficiently merged into a composite shadow volume. Since the shadow volume is a simple polyhedron, its boundary can be represented as a planar graph. The balanced BSP tree together with this graph allow ray coherence and output-sensitive clipping for fast visibility operations. We then generalize the visibility layers to accelerate visibility operations not originated from the source. Finally, we explore the applications of the visibility layers to advanced rendering such as shadow generation with area light sources, ray tracing, radiosity and walkthrough. Our experiments indicate that the visibility layers greatly improve the efficiency of the rendering applications.