Interactive screenspace stream-compaction fragment rendering of direct illumination from area lights

Interactive rendering of illumination from area lights in virtual worlds has always proved to be challenging. In this paper, we extend the work of multi resolution rendering for direct illumination from area lights. We propose a deferred shading method for direct illumination which subdivides screenspace into multi resolution 2D-fragments in which higher resolution fragments are created to represent geometric and depth discontinuities as well as shadow boundaries. To detect shadow boundaries, our subdivision scheme, sub-fragment visibility test (SFVT), performs a visibility discontinuity check within each fragment and subdivides the fragment to a higher resolution level if discontinuity is found. In addition, our proposed gradient aware screenspace subdivision (GASS) algorithm accelerates the refinement by increasing the number of subdivisions based on gradient differences. Our technique utilizes the streamcompaction feature of the transform feedback shader (TFS) in the graphics shading pipeline to filter out fragments for soft shadow refinement. A single pass screenspace irradiance upsampling scheme which uses radial basis functions (RBF) is proposed for interpolating scattered fragments. This reduces artifacts caused by large fragments. Our technique does not require precomputations and is able to run at interactive rates.