The basics behind screen-space ambient occlusion are simple: for each fragment on a screen-filled quad we calculate an occlusion factor based on the fragment's surrounding depth values. This approach is incredibly fast compared to real ambient occlusion and gives plausible results, making it the de-facto standard for approximating real-time ambient occlusion. The technique uses a scene's depth buffer in screen-space to determine the amount of occlusion instead of real geometrical data. In 2007, Crytek published a technique called screen-space ambient occlusion (SSAO) for use in their title Crysis. One could shoot a large number of rays for each point in space to determine its amount of occlusion, but that quickly becomes computationally infeasible for real-time solutions. While not an incredibly obvious effect, the image with ambient occlusion enabled does feel a lot more realistic due to these small occlusion-like details, giving the entire scene a greater feel of depth.Īmbient occlusion techniques are expensive as they have to take surrounding geometry into account. Notice how especially between the creases, the (ambient) light is more occluded: Take a look at the corners and creases of your room to see that the light there seems just a little darker.īelow is an example image of a scene with and without ambient occlusion. These areas are largely occluded by surrounding geometry and thus light rays have fewer places to escape to, hence the areas appear darker. One type of indirect lighting approximation is called ambient occlusion that tries to approximate indirect lighting by darkening creases, holes, and surfaces that are close to each other.

In reality, light scatters in all kinds of directions with varying intensities so the indirectly lit parts of a scene should also have varying intensities. Ambient lighting is a fixed light constant we add to the overall lighting of a scene to simulate the scattering of light. We've briefly touched the topic in the basic lighting chapter: ambient lighting.

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