Preserving Shadow Silhouettes In Illumination-Driven Mesh Reduction

A main challenge for today's renderers is the ever-growing size of 3D scenes, exceeding the capacity of typically available main memory. This especially holds true for graphics processing units (GPUs) which could otherwise be used to greatly reduce rendering time. A lot of the memory is spent on detailed geometry with mostly imperceptible influence on the final image, even in a global illumination context. Illumination-driven mesh reduction, a Monte Carlo-based global illumination simulation, steers its mesh reduction towards areas with low visible contribution. While this works well for preserving high-energy light paths such as caustics, it does have problems: First, objects casting shadows while not being visible themselves are not preserved, resulting in highly inaccurate shadows. Secondly, non-transparent objects lack proper reduction guidance since there is no importance gradient on their backside, resulting in visible over-simplification. We present a solution to these problems by extending illumination-driven mesh reduction with occluder information, focusing on their silhouettes as well as combining it with commonly used error quadrics to preserve geometric features. Additionally, we demonstrate that the combined algorithm still supports iterative refinement of initially reduced geometry, resulting in an image visually similar to an unreduced rendering and enabling out-of-core operation.