Fast object-precision shadow generation for area light source

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Abstract
This paper introduces an efficient object-precision shadow generation algorithm for static polygonal environments directly illuminated by convex area light sources. Penumbra and umbra regions are calculated analytically and represented as a pair of BSP trees for each light source. As the trees are built, convex scene polygons are filtered down the trees, and split into fragments that are wholly lit, in penumbra, or in umbra. The illumination due to the light source is calculated at selected points within the wholly lit and penumbra regions by contour integration with the visible parts of the light source. We use a fast analytic algorithm to compute the fragments of the area light source visible from a point in penumbra. Rendering is done using hardwaresupported linear interpblated shading on a 3D graphics workstation. Because the scene itself is represented as a BSP tree, visible-surface determination may be performed by using either workstation-supported hardware (e.g., a z-buffer) or software BSP-tree traversal. We provide sample images created by our implementation, including timings and polygon counts.

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