Implementing screen space ambient occlusion (SSAO)

We have implemented simple lighting recipes in previous chapters. These unfortunately approximate some aspects of lighting. However, effects such as global illumination are not handled by the basic lights, as discussed earlier. In this respect, several techniques have been developed over the years which fake the global illumination effects. One such technique is Screen Space Ambient Occlusion (SSAO) which we will implement in this recipe.

As the name suggests, this method works in screen space. For any given pixel onscreen, the amount of occlusion due to its neighboring pixels can be obtained by looking at the difference in their depth value. In order to reduce the sampling artefacts, the neighbor coordinates are randomly offset. For a pixel whose depth values are close to one another, they belong to the geometry which is spatially lying close. Based on the difference of the depth values, an occlusion value is determined. Given in pseudocode...