E ective Occlusion Culling for the Interactive Display of Arbitrary Models

HANSONG ZHANG: E ective Occlusion Culling for the Interactive Display of Arbitrary Models. (Under the direction of Dinesh Manocha.) As an advanced form of visibility culling, occlusion culling detects hidden objects and prevents them from being rendered. An occlusion-culling algorithm that can e ectively accelerate interactive graphics must simultaneously satisfy the following criteria: Generality. It should be applicable to arbitrary models, not limited to architectural models or models with many large, polygonal occluders. Signi cant Speed-up. It should not only be able to cull away large portions of a model, but do so fast enough to accelerate rendering. Portability and Ease of Implementation. It should contain as few assumptions as possible on special hardware support. It must also be robust (i.e. insensitive to oating-point errors). Based on proper problem decomposition and e cient representations of cumulative occlusion, this dissertation presents algorithms that satisfy all three of the criteria listed above. Occlusion culling is decomposed into two sub-problems|in order for an object to be occluded by the occluders, its screen-space projection must be inside the cumulative projection of the occluders, and it must not occlude any visible parts of the occluders. These two necessary conditions are veri ed by the overlap tests and the depth tests, respectively. The cumulative projection and the depth of the occluders are represented separately to support these tests. Hierarchical occlusion maps represent the cumulative projection to multiple resolutions. The overlap tests are performed hierarchically through the pyramid. The multi-resolution representation supports such unique features as aggressive approximate culling (i.e. culling away barely-visible objects), and leads to the concept of levels of visibility.