The Two-Level Semi-Synchronous Parallelization Method for the Caustic and Indirect Luminance Calculation in Realistic Rendering

The paper considers an original approach to the semi-synchronous calculation of the luminance of caustic and indirect illumination for the group of methods based on the bidirectional stochastic ray tracing with backward pho-ton maps. The designed parallelization method uses the two-level threads hierarchy. The low level of this thread hierarchy is synchronous calculations of the part of the whole image defined by a randomly generated pixel mask which is applied to the whole image. The top level is semi-synchronous parallelization level that consists groups of the low level threads which of them calculate own part of the whole image in a way similar to asynchronous calculations. As the top level is semi-synchronous it means that when calculating the luminance of the caustic and indirect illumination, the threads of the low level have access to the data accumulated in the backward photon maps of the other parallel threads of the semi-synchronous level. A special algorithm for organizing an access to data of the upper-level threads avoids de-lays associated with data synchronization. The comparison of the developed solution with purely synchronous and asynchronous parallelization methods is presented.