Soft Shadows by Ray Tracing Multilayer Transparent Shadow Maps

We present a method for high quality soft shadows for area lights in cinematic lighting. The method is an extension of traditional shadow maps, so it has the advantage of image based shadow methods; the algorithm’s complexity is independent of geometric complexity. We introduce multilayer transparent shadow maps, which can be used to produce high quality soft shadows for scenes with extremely complex geometry, fur, and volume objects. Instead of the traditional sampling and filtering of shadow maps, we compute the shadow factor by ray tracing the multilayer transparent shadow map. The result is soft shadows of quality similar to that achieved by stochastic ray tracing, but at a much lower cost.