For more information about PCSS, please refer to the integration guide and other resources listed below. It produces perceptually plausible soft shadows that harden on contact (see screenshot above). The Percentage-Closer Soft Shadows (PCSS) algorithm computes a variable kernel size based on the distance between the relative position of the receiver point, an approximation of the blocker, and the area light. Soft shadows are typically rendered in games by using shadow mapping and Percentage Closer Filtering with a uniform kernel size. Also, while the kernel size and penumbra width is uniform, the kernel can be scaled to accomodate different sized lights. The PCF algorithm is very straightforward and fast, but does not achieve a realistic contact hardening effect. The Percentage Closer Filtering technique uses a uniform size filter kernel, resulting in shadows with a uniformly soft edge due. To avoid self-shadowing artifacts, an additional depth bias may also been applied while writing depth into the shadow map.
The sample uses a gradient-based depth bias to scale the depth bias based on the uv-space distance from the center of the kernel. This sample is assuming the shadow map is a regular depth buffer (non-linear depths), and the shadow-map is generated using a perspective projection with the center of projection at the center of the area light simulated by PCSS. This sample demonstrates three techniques for rendering soft shadows: Percentage Closer Filtering (PCS) with a uniform kernel size, Percentage-Closer Soft Shadows (PCSS) with a variable kernel size, and Contact Hardening Shadows (CHS) with a dynamically generated fixed size kernel.
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