Multi-Fragment Rendering for Glossy Bounces on the GPU

Abstract

Multi-fragment rendering provides additional degrees of freedom in postprocessing. It allows us to edit images rendered with antialiasing, motion blur, depth of field, and transparency. To store multiple fragments, relationships between pixels and scene elements are often encoded into an existing image format. Most multi-fragment rendering systems, however, take into account only directly visible fragments on primary rays. The pixel coverage of indirectly visible fragments on reflected or refracted rays has not been well discussed. In this paper, we extend the generation of multiple fragments to support the indirect visibility in multiple bounces, which is often required by artists for image manipulation in productions. Our method is compatible with an existing multi-fragment image format such as Cryptomatte, and does not need any additional ray traversals during path tracing.