Abstract: Soft shadow mapping is an attractive solution to the problem of real-time soft shadows because it works with any kind of rasterizable geometry (in particular alpha-transparent textures and hair), it does not require any precomputation, and it is simple to implement on the GPU. However, state-of-the-art approaches have several limitations that prevent them from being practical for all scenes. First, parameter tuning is required to avoid surface acne. Second, gaps between shadow-map pixels are either ignored, which results in light bleeding, or handled using gap filling, which results in overshadowing.

We present a more robust soft shadow mapping technique, based on a recent backprojection algorithm, that uses depth peeling to address the problems of surface acne and light bleeding. Our algorithm uses a multi-layer shadow map to reduce light bleeding, and midpoint shadow maps to handle self-shadowing more robustly. It provides high-quality soft shadowing for complex scenes, while still maintaining interactive rendering rates. Source code is available online.