5 Disabling computation on a sparse subset of stream elements is itself a difficult problem. Researchers have used the depth buffer, stencil buffer, substreams (drawing smaller sets of geometry), and other tricks to prevent stream elements from being processed. NVIDIA GeForce 6 Series GPUs have full support for branching in the vertex processor and a limited form of branching in the fragment processor. Combining conditional execution with data-parallel computation is an active area of research.