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 pass from the light, in contrast to using depth peeling and one pass per layer. For closed objects, we also suppress the need for a bias. The method is extended to soft shadow sampling for an arbitrarily shaped area-/volumetric light source using 128-1024 light samples per screen pixel. The alias-free shadow map guarantees that the visibility is accurately 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 borders due to normal interpolation.

@Article { SEA08a,
  author       = "Sintorn, Erik and Eisemann, Elmar and Assarsson, Ulf",
  title        = "Sample-based visibility for soft shadows using alias-free shadow maps",
  journal      = "Computer Graphics Forum (Proc. of EGSR)",
  number       = "4",
  volume       = "27",
  pages        = "1285--1292",
  month        = "June",
  year         = "2008",
  keywords     = "Shadows, alias-free, GPU",
  url          = "http://graphics.tudelft.nl/Publications-new/2008/SEA08a"
}