Conservative Z-prepass for frustum-traced irregular Z-buffers

Abstract

This paper presents a pipeline to accelerate frustum traced irregular z-buffers (IZBs). The IZB proposed by Wyman et al. is used to render accurate hard shadows for real-time applications such as video games, while it is expensive compared to shadow mapping. To improve the performance of hard shadows, we use a two-pass visibility test by integrating a conservative shadow map into the pipeline of the IZB. This paper also presents a more precise implementation of the conservative shadow map than the previous implementation. In our experiments for 4K screen resolution, the performance of the hard shadow computation is improved by more than double on average using the two-pass visibility test, though there is still room for optimization.