Efficient visibility projection on spherical polar coordinates for shadow rendering using geometry shader.

Visibility precomputation has become essential for PRT-based rendering involving soft shadows. While graphic hardware rasterization has been increasingly used to compute visibility information for a mass of precomputation tasks, the linear feature of rasterization makes it unadaptive to sample visibility in a coordinates system, to which the Cartesian coordinates are non-linearly mapped. With the emergence of Geometry Shader in the framework of DirectX 10, this problem can be solved. In this paper, we present an efficient solution for visibility sampling on the spherical polar coordinates in the precomputation stage of PRT by means of the Geometry Shader within the DirectX 10 pipelines. In the mean time, a spherical reparameterization scheme is introduced for shadow rendering, under which spherical functions as lighting, BRDF and visibility are mapped onto the spherical polar coordinates.