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Abstract

Significant advances have been achieved for realtime ray
tracing recently, but realtime performance for complex
scenes still requires large computational resources not yet
available from the CPUs in standard PCs. Incidentally, most
of these PCs also contain modern GPUs that do offer much
larger raw compute power. However, limitations in the
programming and memory model have so far kept the
performance of GPU ray tracers well below that of their CPU
counterparts.

In this paper we present a novel packet ray traversal
implementation that completely eliminates the need for
maintaining a stack during kd-tree traversal and that
reduces the number of traversal steps per ray. While CPUs
benefit moderately from the stackless approach, it improves
GPU performance significantly. We achieve a peak performance
of over 16 million rays per second for reasonably complex
scenes, including complex shading and secondary rays.
Several examples show that with this new technique GPUs can
actually outperform equivalent CPU based ray tracers.