Conservative Volumetric Visibility with Occluder Fusion

Visibility determination is a key requirement in a wide range of graphics applications. This work introduces a new approach to the computation of volumetric visibility, the detection of occluded portions of space as seen from a given region. The method is conservative and classifies regions as occluded only then they are guatanteed to be invisible. It operates on a discrete representation of space and uses the opaque interior of objects as occluders. This choice of occluders facilitates their extension into opaque regions of space, in essence maximizing their size and impact. Out method efficiently detects and represents the regions of space hidden by such occluders and is the first one to use the property that occluders can also be extended into empty space provides that space is itself occluded as seen from the viewing volume. This proves extremely effective for computing the occlusion by a set of occluders, effectively realizing occluder fusion. An auxiliary data structure represents occlusion in the scene, which can then be querried to answer volume visibility questions. We demonstrate the applicability to visibility preprocessing for real-time walkthroughs anbd to shadow-ray acceleration for extended light sources in ray tracing, with significant speed-up in all cases.