Variance Soft Shadow Mapping

Abstract

We present variance soft shadow mapping (VSSM) for rendering plausible soft shadow in real-time. VSSM is based on the theoretical framework of percentage-closer soft shadows (PCSS) and exploits recent advances in variance shadow mapping (VSM). Our new formulation allows for the efficient computation of (average) blocker distances, a common bottleneck in PCSS-based methods. Furthermore, we avoid incorrectly lit pixels commonly encountered in VSM-based methods by appropriately subdividing the filter kernel. We demonstrate that VSSM renders high-quality soft shadows efficiently (usually over 100 fps) for complex scene settings. Its speed is at least one order of magnitude faster than PCSS for large penumbra.