Catmull-Clark subdivision for geometry shaders

Subdivision surfaces possess many appealing properties applicable to interactive computer graphics. However, the necessity to access a variable-sized neighborhood in a control mesh makes it difficult to efficiently accelerate tessellation calculations in graphics hardware. The paper addresses this problem in two ways. First, it proposes a simple and inexpensive calculation scheme for the tessellation of Catmull-Clark subdivision surfaces which can be implemented in a geometry shader. It operates on the shader's vertex input only and does not require external texture memory access or multi-pass processing for tessellation. Second, the paper presents an extension to the post-transform and lighting (T'n'L) vertex cache operation that efficiently accelerates the processing of variable-size primitives serving as input for the geometry shader. We demonstrate on-chip tessellation of Catmull-Clark subdivision surfaces on an embedded hardware implementation. The described calculation scheme will be implementable on desktop hardware if limitations on the maximal input primitive size for the geometry shader are relaxed.