Temporally coherent conservative visibility

EEciently identifying polygons that are visible from a changing synthetic viewpoint is an important problem in computer graphics. Even with hardware support, simple algorithms like depth-buuering cannot achieve interactive frame rates when applied to geometric models with many polygons. However, a visibility algorithm that exploits the occlu-sion properties of the scene to identify a superset of visible polygons, without touching most invisible polygons, could achieve fast frame rates while viewing such models. In this paper, we present a new approach to the visibility problem. The novel aspects of our algorithm are that it is temporally coherent and conservative; for all viewpoints the algorithm overestimates the set of visible polygons. As the synthetic viewpoint moves, the algorithm reuses visibility information computed for previous viewpoints. It does so by computing visual events at which visibility changes occur , and eeciently identifying and discarding these events as the viewpoint changes. In essence, the algorithm implicitly constructs and maintains a linearized portion of an aspect graph, a data structure for representing visual events. 1 Introduction In computer graphics, identifying visible polygons or eliminating hidden polygons is an important component of ef-cient scene rendering algorithms. Despite the availability of the depth-buuer algorithm in hardware 2], the number of polygons in many geometric models is larger than hardware alone can process at interactive frame rates. One way to address this problem is by developing algorithms that resolve visibility at a higher level, and render only the visible portions of the model. Approximation algorithms that overestimate the set of visible polygons are useful, if they