“Displacement Mapping with Ray-casting in Hardware” by Yerex and Jagersand

Traditionally, displacement maps have been rendered with micropolygons [Cook et al. 1987]. In both raytracers and real-time systems, these high polygon counts lead to memory/bandwidth inefficiency, and high geometric transformation costs, which limit performance. Recently, displacement maps have also been directly rendered in raytracing, using iterative root-finding methods [Heidrich and Seidel 1998]. Here, we propose a similar ray intersection approach for real-time rendering. However, an iterative solution is infeasible in graphics hardware due to the limitations on texture indirections. A texture indirection occurs when the results of one texture access affect the coordinates of subsequent accesses, such as in each step of an iterative solution. These are currently limited to 4 on Radeon 9700/9800 where in contrast, a possible total of 32 texture accesses are allowed per fragment. This has led us to the hybrid sampling/iterative approach described here