Projection-driven grid-BSP tree for real-time trimming on GPU

Abstract

In Computer Aided Design (CAD), trimmed non-uniform rational B-spline (NURBS) is the industrial standard to represent the shapes of models. Trimming, the process of removing unnecessary portions of a surface, remains a major performance bottleneck in the recent CAD model rendering methods based on real-time surface tessellation. In this paper, we identify the core reasons for the inefficiency in existing real-time trimming methods, and present a new trimming method that incurs nearly no cost in the state-of-the-art NURBS surface rendering pipeline. Our approach begins with building a projection-driven grid-bsp-tree with a fixed depth of two and leaf nodes containing only one single curve segment, effectively minimizing the overall cost of tree traversal and ray-curve intersections. Additionally, we reduce the cost of trimming tests by approximating trimming curves into poly-lines while keeping the storage consumption at a minimum, where the quality of the approximation is measured by a novel on-surface error metric. Compared with existing works, our method achieves consistent error control for across the entire model using a more reasonable error metric while requiring less memory. Compared to the previous kd-tree-based method, our method achieves a 70% speedup, reducing the trimming process to just 5% of the total rendering time, effectively eliminating it as a major performance bottleneck. Due to its superior performance, our method provides significant advantages for rendering large-scale CAD models.