Abstract c
Abstract:
Ray tracing has produced some of the most realisti omputer generated pictures to date. They contain surface T texturing, local shading, shadows, reflections and refractions he major disadvantage of ray tracing results from its pointt e sampling approach. Because calculation proceeds ab initio a ach pixel it is very CPU intensive and may contain notice-t able aliasing artifacts. It is difficult to take advantage of spa ial coherence because the shapes of reflections and refractions from curved surfaces are so complex. In this paper we describe an algorithm that utilizes the f spatial coherence of polygonal environments by combining eatures of both image and object space hidden surface algo-w rithms. Instead of tracing infinitesimally thin rays of light e sweep areas through a scene to form "beams. " This techr t nique works particularly well for polygonal models since fo his case the reflections are linear transformations, and refractions are often approximately so. The recursive beam tracer begins by sweeping the proa jection plane through the scene. Beam-surface intersections re computed using two-dimensional polygonal set operations h and an occlusion algorithm similar to the Weiler-Atherton idden surface algorithm. For each beam-polygon intersecr tion the beam is fragmented and new beams created for the eflected and transmitted swaths of light. These sub-beams s are redirected with a 4x4 matrix transformation and recur ively traced. This beam tree is an object space representa-
