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From: tarolli@westcoast.esd.sgi.com (Gary Tarolli)
Newsgroups: comp.sys.sgi
Subject: Re: question on gl
Summary: the real truth
Message-ID: <94881@sgi.sgi.com>
Date: 2 Apr 91 17:44:41 GMT
References: <14144@medusa.cs.purdue.edu> <1991Apr2.150125.22972@odin.corp.sgi.com>
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Organization: Silicon Graphics, Inc., Mountain View, CA
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In article <1991Apr2.150125.22972@odin.corp.sgi.com>, dave@sgi.com (dave "who can do? ratmandu!" ratcliffe) writes:
> In article <14144@medusa.cs.purdue.edu> avr@cs.purdue.EDU (Andrew V. Royappa) writes:
> >The gl graphics user's guide says that the perspective & viewing
> >transformations transforms the perspective pyramid into the box 
> >-1.0 <= x,y,z <= 1.0, to facilitate clipping. Is this in fact
> >the case, 
> yep--this *is* the case -1.0 to 1.0 for x, y, *and* z clipping.
> 

actually we clip against -w and +w, where w is normally 1.0 for orthographic
projections.  For perspective transformations, w is NOT 1.0, and instead of
transforming the pyramid into a unit box, we really do clip against the 
pyramid.  

--------------------
	Gary Tarolli