Global Illumination: Ambient Occlusion

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Some self-shadowing effects can be obtained less expensively:

Ambient Occlusion is a “hack” to create more realistic ambient illumination cheaply

How it is done:

Assume light from everywhere is partially blocked by local objects.

From a point on the surface, cast many rays at random.

Ambient term is proportional to percent of rays that hit "nothing" (or the "sky').

Weight average by cosine of angle with normal
(assuming sky is brightest at zenith).

Consider distance before ray is occluded
(close obstructions cause more shadowing).

A more complicated example:   nVidia Gelato Demo Image

Looks like a scene that has been spray-painted in matte gray on a foggy day ...

To learn more:

(This is material that you should look at if you choose Ambient Occlusion as your project extension, but it will not be on the Final Exam.)

GPU Gems 2: Chapter 14. Dynamic Ambient Occlusion and Indirect Lighting  by Michael Bunnell, NVIDIA Corporation

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