Efficient Evaluation of Semi-Smooth Creases in Catmull-Clark Subdivision Surfaces

Abstract

We present a novel method to evaluate semi-smooth creases in Catmull-Clark subdivision surfaces. Our algorithm supports both integer and fractional crease tags corresponding to the RenderMan (Pixar) specification. In order to perform fast and efficient surface evaluations, we obtain a polynomial surface representation given by the semismooth subdivision rules. While direct surface evaluation is applied for regular patches, we perform adaptive subdivision around extraordinary vertices. In the end, we are able to efficently handle high-order sharpness tags at very low cost. Compared to the state-of-the art, both render time and memory consumption are reduced from exponential to linear complexity. Furthermore, we integrate our algorithm in the hardware tessellation pipeline of modern GPUs. Our method is ideally suited to real-time applications such as games or authoring tools.