Real-time Soft Shadow Mapping by Backprojection
Eurographics Symposium on Rendering 2006, Nicosia, Cyprus.
We present a new real-time soft shadow algorithm using a single shadow map per light source. Therefore, our algorithm is well suited to render both complex and dynamic scenes, and it handles all rasterizable geometries. The key idea of our method is to use the shadow map as a simple and uniform discretized represention of the scene, thus allowing us to generate realistic soft shadows in most cases. In particular it naturally handles occluder fusion. Also, our algorithm deals with rectangular light sources as well as textured light sources with high precision, and it maps well to programmable graphics hardware.
See also our paper High-Quality Adaptive Soft Shadow Mapping (EG2007) that significantly improves this approach using a contour detection algorithm with radial integration and various adaptive precision strategies.
A scene including alpha-textured meshes (foliage and wire netting). Left: illustration of realistic soft shadows produced by the average of 1024 hard shadows (2.5s per frame). Right: our new soft shadow algorithm rendering the same scene at 25 fps without any precomputation.
Quality comparison - From left to right: our algorithm, reference image, the penumbra wedges [SIG03] and the flood-fill algorithm [EG04].