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View Full Version : What the hell is Carmack's Reversed Unreversed Thing?



Devulon
02-19-2002, 02:03 PM
That Subject makes this sound like a Technical question. I know the topics are talking abot shadow volumes but the question is, how does this relate to carmack? Did he write an article or something ? Have I been living in a hole for too long programming opengl ?

Zeno
02-19-2002, 02:28 PM
It's just a different (reversed) way of incrementing and decrementing the stencil buffer while doing stenciled shadow volumes.

-- Zeno

jwatte
02-19-2002, 03:04 PM
It means you increment/decrement when you FAIL the depth test (alternately, when you pass the reverse depth test). In that case, you will not get artifacts when an un-capped shadow volume intersects the near plane, but you'll still get artifacts when it intersects the far plane (which is unlikely in an indoor shooter kind of game).

It's known as Carmack's reverse because he's described this as being what he's using in his current code, in some .plan file or something (I don't have the actual reference to point you at).

bpeers
02-28-2002, 07:32 AM
Er, wasn't it more like, he is capping (closing) the shadow volume, but when it hits the far plane, it needs to be clipped which is difficult/ugly, so instead he just pushes the far plane further back (which he can do because he only uses ranged lights).

Not sure though http://www.opengl.org/discussion_boards/ubb/smile.gif