Sample Based Visibility for Soft Shadows using Alias-free Shadow Maps

This paper introduces an accurate real-time soft shadow algorithm that uses sample based visibility. Initially,we present a GPU-based alias-free hard shadow map algorithm that typically requires only a single render passfrom the light, in contrast to using depth peeling and one pass per layer. For closed objects, we also suppress theneed for a bias. The method is extended to soft shadow sampling for an arbitrarily shaped area-/volumetric lightsource using 128-1024 light samples per screen pixel. The alias-free shadow map guarantees that the visibility isaccurately sampled per screen-space pixel, even for arbitrarily shaped (e.g. non-planar) surfaces or solid objects. Another contribution is a smooth coherent shading model to avoid common light leakage near shadow bordersdue to normal interpolation