BEAM TRACING POLYGONAL OBJECTS.

Abstract

An algorithm is described that utilizes the spatial coherence of polygonal environments by combining features of both image and object space hidden surface algorithms. Instead of tracing infinitesimally thin rays of light, we sweep areas through a scene to form beams. This technique works particularly well for polygonal models since for this case the reflections are linear transformations, and refractions are often approximately so. The recursive beam tracer begins by sweeping the projection plane through the scene. Beam-surface intersections are computed using two-dimensional polygonal set operations and an occlusion algorithm similar to the Weiler-Atherton hidden surface algorithm. For each beam-polygon intersection the beam is fragmented and new beams created for the reflected and transmitted swaths of light. These sub-beams are redirected with a 4 multiplied by 4 matrix transformation and recursively traced. This beam tree is an object space representation of the entire picture.