ATVI-TR-16-01: Practical Realtime Strategies for Accurate Indirect Occlusion

Ambient occlusion is ubiquitous in games and other real-time applications to approximate global illumination effects. However there is no analytic solution to ambient occlusion integral for arbitrary scenes, and using general numerical integration algorithms is too slow, so approximations used in practice often are empirically made to look pleasing even if they don’t accurately solve the AO integral. In this work we introduce a new formulation of ambient occlusion, GTAO, which is able to match a ground truth reference in half a millisecond on current console hardware. This is done by using an alternative formulation of the ambient occlusion equation, and an efficient implementation which distributes computation using spatio-temporal filtering. We then extend GTAO with a novel technique that takes into account near-field global illumination, which is lost when using ambient occlusion alone. Finally, we introduce a technique for specular occlusion, GTSO, symmetric to ambient occlusion which allows to compute realistic specular reflections from probe-based illumination. Our techniques are efficient, give results close to the ray-traced ground truth, and have been integrated in
recent AAA console titles.

Click here to read the full technical report: PDF