This shows an implementation of a Depth Pass : a pre-process of the scene of opaque objects so as to render the ZBuffer first with a simple shader override,
then rendering the scene again by changing the ZCompare function to LESSEQUAL, we can quickly discard objects that will be masked by other objects in front of them.
In a word : that simply helps to render opaque pixels only once (which can dramatically increase render time when using complicated shaders !)
NOTE: This also yields the Z-buffer that we can use in post-process passes. ^_^
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Use Alt+Shift+Mouse to manipulate the camera using UnrealEd mode (i.e. first person).
If you are under Linux and can't use the Alt key, push that button so everything works without Alt.