Non-homogeneous grids for CPU-GPU ray tracing

Abstract

Ray tracing is among the most resource consuming methods for realistic image generation. Over the years, different acceleration structures have been proposed to reduce ray-object intersection queries since these dominate execution time. Regular grids are one of the most popular structures due to their simplicity and effectiveness. However, regular grid implementations are plagued by two major issues: underwhelming performance on irregular scenes with unbalanced triangle density and high memory consumption due to the many empty cells in sparsely populated scenes, typical of many game scenarios. We present a novel hybrid solution based on non-homogeneous rectilinear grids to improve ray tracing performance on uneven scene distributions. Additionally, we use hashing to get rid of empty cells. Non-homogeneous grids feature moveable split planes along the three axes unlike regular grids where split planes must be equidistant. Our approach performs serial construction tasks such as compression in the CPU and offloads the remaining data parallel tasks to the GPU. Using this acceleration structure we are able to render a wide range of scenes at high frame rates on commodity graphics hardware, from irregular density low polygon count models to regular density high polygon count scanned scenes with rapid construction times and a small memory footprint. For some test cases, our approach nearly doubles the frame rate of a regular grid at a similar resolution, while featuring low build times.