Multi-pass Gaussian Contact-hardening Soft Shadows

Real-time soft shadows have seen numerous improvements over the years. Post-process blurring of shadow edges are commonly used to hide aliasing artifacts, but in some cases, such as ours, it is used to mimic physical processes. Instead of generating penumbra regions uniformly, we scale key algorithmic components in screen space to allow the penumbra region to grow in accordance with occluder/receiver distance. This form of soft shadowing is known to some as contact-hardening and has been explored in various ways. We present an algorithm that explores three ways of achieving contact-hardening soft shadows. Two of those ways are similar in nature to previous works while the third is a novel approach that utilizes occluder distance as a counter for multiple Gaussian passes. Our main contributions are fast occluder approximation and the use of occluder distance to control the number of Gaussian passes. Multiple Gaussian passes create better results than a single Gaussian pass for several scenes, and we explore various ways of improving the performance of the multi-pass approach.