Ray-Patch Intersection for Improving Rendering Quality of Per-pixel Displacement Mapping

Recent GPU advances have popularized pixel-shader based techniques for per-pixel displacement mapping. An important step in the process is to compute intersection of ray with a bilinear patch approximating the displacement map. Accurate ray-patch intersection can significantly enhance the quality of rendered images. However, the increase in quality comes at a significant computation cost resulting in a substantial drop in performance. This paper explores this trade-off between computation and quality. We propose several techniques for ray-patch intersection and compare it to exact ray-quadric/ray-bilinear intersection proposed previously. We show that our quadric based local-gradient-plane approximation achieves a comparable visual quality with a significant performance improvement.