Multi-layer dual-resolution screen-space ambient occlusion

Ambient occlusion (AO) is a lighting model that approximates the diffuse illumination of a surface based on its directly visible occluders. It can be rendered by tracing rays through the normal-oriented unit hemisphere, and returning the percentage of rays that do no hit any geometry at a distance d < R. Screen-space ambient occlusion (SSAO) is an image-based approach that uses the depth buffer of the current rendered scene as an approximation of its geometry. Therefore, compared to other AO algorithms such as ray tracing, SSAO has the advantage of handling dynamic geometry with significantly lower overhead.