This code shows the method described in ShaderX3 article "Fractional disk soft shadows". It shows a simple, practical, and fairly effective way to approximate soft shadows. The actual implementation is a slight modification of percentage closer filtering (PCF). PCF was originally designed to address the aliasing problem inherent in shadow mapping. It also has the welcome side effect of generating soft shadow edges, which resemble simple constant-width penumbrae. In this sample we will show how a slightly modified PCF algorithm can produce more realistic penumbrae. We will use stochastic sampling varied per pixel to obtain reasonable results while using fewer shadow map samples.