The Irregular Z-Buffer and its Application to Shadow Mapping

Gregory S. Johnson, William R. Mark, and Christopher A. Burns

The University of Texas at Austin, Department of Computer Sciences. Technical Report TR-04-09
April 15, 2004


The classical Z-buffer algorithm samples a scene at regularly spaced points on an image plane. We present an extension of this algorithm called the irregular Z-buffer that permits sampling of the scene at arbitrary points on the image plane. The sample points are stored in a two-dimensional spatial data structure which is queried during rasterization. The irregular Z-buffer can be applied to shadow rendering, where we demonstrate that it eliminates the sampling artifacts previously associated with shadow mapping. We describe the extensions to modern graphics hardware necessary to support efficient operation of the irregular Z-buffer, and simulate the performance on the extended hardware. Our results indicate that the irregular Z-buffer can be used to produce hard shadows that are as accurate as those produced by a ray tracer or shadow volume-based renderer. We also find that shadow mapping on the irregular Z-buffer retains many of the performance and applicationdevelopment simplicity advantages of standard shadow mapping.

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