Path: utzoo!attcan!uunet!mailrus!uflorida!mephisto!mcnc!rti!stdc01!rivera
From: rivera@stdc01.UUCP (Greg Rivera)
Newsgroups: comp.graphics
Subject: Wanted: Fast Transformations of 3D Clipping Planes
Message-ID: <628@stdc01.UUCP>
Date: 29 Jun 90 15:37:22 GMT
Reply-To: uucp!rti.rti.org!stdc01!rivera  (Greg Rivera)
Organization: Star Technologies, Graphicon Products Division (RTP, N.C)
Lines: 36

Wanted:
	a) Fast ways to transform plane equations through arbitrary
	matrices, OR
	b) Fast ways to transform eye-clipping planes so I can do
	clipping in some other coordinate space (still in 3D)

Problem:
	My view clipping planes (top, bottom, left, right, near, far)
	are defined in eye space.  But my models (oodles, and moving
	all the time) are defined relative to their own coordinate system.
	Therefore, to do culling/clipping, I either:
	A) Transform every model into eye space, then cull/clip, or
	B) transform the clipping planes into the model's space, so I can
	cull/clip there.
	
	I would like to have suggestions for how to do (B) quickly.

For thought:
	Are there any advantages due to the clipping planes inter-relationships?
	For example, near and far planes are usually parallel.
	Also, for perspective, all four side planes meet at a common point.
	Or are there speedups if the model transformation is of a special
	form, like rotates only (orthonormal)?

	Currently, I'm stuck with sampling 3 points per plane (some are shared)
	and transforming them into model space.  After a cross product and
	normalization to get the normal to the plane, one extra dot gets
	the distance to finish off the plane equation to get Ax+By+Cz+D=0.
	Total is 5 transforms, 5 cross products with normalizations, and
	6 dots (assumes parallel near/far).

Please email suggestions.  Thanks.
-- 
-- Gregory Rivera            Email:       ...{!sun}!rti.rti.org!stdc01!rivera --
-- "... and the wisdom to    Paper: Graphicon, P.O. Box 13951, RTP, NC  27709 --
--  know the difference."    Voice: (919)361-3848           Fax:(919)361-3888 --