In this paper we propose a new method for rendering soft shadows at interactive frame rates. Although the algorithm only uses information obtained from a single light source sample, it is capable of producing subjectively realistic penumbra regions. We do not claim that the proposed method is physically correct but rather that it is aesthetically correct. Since the algorithm operates on sampled representations of the scene, the shadow computation does not directly depend on the scene complexity. Having only a single depth and object ID map representing the pixels seen by the light source, we can approximate penumbrae by searching the neighborhood of pixels warped from the camera view for relevant blocker information. We explain the basic technique in detail, showing how simple observations can yield satisfying results. We also address sampling issues relevant to the quality of the computed shadows, as well as speed-up techniques that are able to bring the performance up to interactive frame rates.
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