Vectorized Production Path Tracing

This paper presents MoonRay, a high performance production rendering architecture using Monte Carlo path tracing developed at DreamWorks Animation. MoonRay is the first production path tracer, to our knowledge, designed to fully leverage Single Instruction/Multiple Data (SIMD) vector units throughout. To achieve high SIMD efficiency, we employ Embree for tracing rays and vectorize the remaining compute intensive components of the renderer: the integrator, the shading system and shaders, and the texturing engine. Queuing is used to help keep all vector lanes full and improve data coherency. We use the ISPC programming language to achieve improved performance across SSE, AVX/AVX2 and AVX512 instruction sets. Our system includes two functionally equivalent uni-directional CPU path tracing implementations: a C++ scalar depth-first version and an ISPC vectorized breadth-first wavefront version. Using side by side performance comparisons on complex production scenes and assets we show our vectorized architecture, running on AVX2, delivers between a 1.3x to 2.3x speed-up in overall render time, and up to 3x, 6x, and 4x, speed-ups within the integration, shading, and texturing components, respectively.