SobolBurleySequence

Owen-scrambled Sobol by hashing (Burley 2020), the default sequence.

In the namespace construct::pathtrace. Declared in src/libs/libconstruct/construct/pathtrace/SampleSequence.hpp.

Detailed description

Brent Burley, "Practical Hash-based Owen Scrambling", JCGT 9(4), 2020, https://jcgt.org/published/0009/04/01/. Each pixel scrambles one Sobol sequence with a seed of its own, and each group of four dimensions with another, so the values are stratified per pixel and independent between pixels and groups. No table larger than the four direction vectors.

The first sample of each pixel comes from a different place: the Sobol point at the pixel's shuffled Morton index, with one seed for all pixels. Neighboring pixels then take neighboring points of one sequence, so a frame of one sample is evenly spread rather than grainy: the "blue-noise first" of Cycles (§RVR-3).