MergeTree: a HLBVH constructor for mobile systems

Powerful hardware accelerators have been recently developed that put interactive ray-tracing even in the reach of mobile devices. However, supplying the rendering unit with up-to date acceleration trees remains difficult, so the rendered scenes are mostly static. The restricted memory bandwidth of a mobile device is a challenge with applying GPU-based tree construction algorithms. This paper describes MergeTree, a BVH tree constructor architecture based on the HLBVH algorithm, whose main features of interest are a streaming hierarchy emitter, an external sorting algorithm with provably minimal memory usage, and a hardware priority queue used to accelerate the external sort. In simulations, the resulting unit is faster by a factor of three than the state-of-the art hardware builder based on the binned SAH sweep algorithm.