Global visibility algorithms for illumination computations
SIGGRAPH '93 Proceedings of the 20th annual conference on Computer graphics and interactive techniques
A fast shadow algorithm for area light sources using backprojection
SIGGRAPH '94 Proceedings of the 21st annual conference on Computer graphics and interactive techniques
Fast computation of shadow boundaries using spatial coherence and backprojections
SIGGRAPH '94 Proceedings of the 21st annual conference on Computer graphics and interactive techniques
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Modeling the effects of area light sources has been an active area of research for many years. Most methods simplify the problem by approximating the area source with a collection of point sources. The only existing analytic methods work in screen space to compute a single image. This paper presents an object-space algorithm to model illumination from polygonal light sources, as well as point sources. The result is a collection of smooth-shaded polygonal facets that may be rendered from any viewing position. Binary Space Partitioning trees are used to compute the umbra and penumbra boundaries efficiently. Fast analytic techniques are developed for illumination calculations. Numerical optimization techniques are used to sample the shading function finely enough to find all significant illumination gradations. Illumination calculations are optimized to concentrate computational effort on parts of the scene where they are most needed.