Efficient Complete Radiosity Ray Tracing Using a Shadow Coherence Method

摘要

Most two pass radiosity methods calculate, in a preprocessing step for each patchor element in a scene, a radiosity shading that contains both the intensity of the light that is received directly from the main light sources and the intensity of the light that is received indirectly by means of diffuse and specular interreflection between patches. However, it is very difficult to represent accurately the distribution of the radiosity shading over the patch, in particular where sharp shadows exist. A better approach, therefore, is to store only the indirect reflection component, which is fairly constant over the patch, in the form of radiosity shading, and to calculate the direct reflection component, which is responsible for the larger part of the intensity variation, during the second pass by casting shadow rays. The number of shadow rays for the direct light computation can be kept low by selecting only those light sources that substantially contribute to the shading of a patch, and by applying an adaptive image refinement technique in combination with a shadow coherence method.