Soft Shadow Maps for Linear Lights

Soft shadows and penumbra regions generated by extended light sources such as linear and area lights are visual effects that significantly contribute to the realism of a scene. In interactive applications, shadow computations are mostly performed by either the shadow volume or the shadow map algorithm. Variants of these methods for soft shadows exist, but they require a significant number of samples on the light source, thereby dramatically increasing rendering times. In this paper we present a modification to the shadow map algorithm that allows us to render soft shadows for linear light sources of a high visual fidelity with a very small number of light source samples. This algorithm is well suited for both software and hardware rendering.