RMIP: Displacement ray tracing via inversion and oblong bounding

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.