Accelerating Rendering of NURBS Surfaces by Using Hybrid Ray Tracing

In this paper we present a new method for accelerating ray tracing of scenes containing NURBS (Non Uniform Rational B-Spline) surfaces by exploiting the GPU’s fast z-buffer rasterization for regular triangle meshes. In combination with a lightweight, memory efficient data organization this allows for fast calculation of primary ray intersections using a Newton Iteration based approach executed on the CPU. Since all employed shaders are kept simple the algorithm can profit from older graphics hardware as well. We investigate two different approaches, one initiating ray-surface intersections by referencing the surface through its child-triangles. The second approach references the surface directly and additionally delivers initial guesses, required for the Newton Iteration, using graphics hardware vector interpolation capabilities. Our approaches achieve a rendering acceleration of up to 95% for primary rays compared to full CPU ray tracing without compromising image quality.