High-performance ray tracing of triangle meshes equipped with displacement maps is a challenging task. Existing methods either rely on pre-tessellation, taking full advantage of the hardware but with a poor memory/quality tradeoff, or use custom displacement-centric acceleration structures, preserving all the geometric details but being orders of magnitude slower. We introduce a method that efficiently probes the displacement-map space to find ray-surface intersections without relying on pre-tessellation. Our method combines inverse displacement mapping and on-the-fly surface-bound computation. It employs a novel data structure that provides tight displacement bounds over rectangular regions in the displacement-map space. We demonstrate the effectiveness of our approach in a production GPU path tracer. It can achieve over an order of magnitude speed-up in render time compared to state of the art in the most challenging real-time path-tracing scenarios, while maintaining a low memory footprint.

Displacement mapping is a powerful mechanism for adding fine to medium geometric details over a 3D surface using a 2D map encoding them. While GPU rasterization supports it through the hardware tessellation unit, ray tracing surface meshes textured with high quality displacement requires a significant amount of memory. More precisely, the input surface needs to be pre-tessellated at the displacement map resolution before being enriched with its mandatory acceleration data structure. Consequently, designing displacement maps interactively while enjoying a full physically-based rendering is often impossible, as simply tiling multiple times the map quickly saturates the graphics memory. In this work we introduce a new tessellation-free displacement mapping approach for ray tracing. Our key insight is to decouple the displacement from its base domain by mapping a displacement-specific acceleration structures directly on the mesh. As a result, our method shows low memory footprint and fast high resolution displacement rendering, making interactive displacement editing possible.