Reducing shading on GPUs using quad-fragment merging

Abstract

Current GPUs perform a significant amount of redundant shading when surfaces are tessellated into small triangles. We address this inefficiency by augmenting the GPU pipeline to gather and merge rasterized fragments from adjacent triangles in a mesh. This approach has minimal impact on output image quality, is amenable to implementation in fixed-function hardware, and, when rendering pixel-sized triangles, requires only a small amount of buffering to reduce overall pipeline shading work by a factor of eight. We find that a fragment-shading pipeline with this optimization is competitive with the REYES pipeline approach of shading at micropolygon vertices and, in cases of complex occlusion, can perform up to two times less shading work.