question on gl

[Gary Tarolli]

In article <1991Apr2.150125.22972 at odin.corp.sgi.com>, dave at sgi.com (dave "who can do? ratmandu!" ratcliffe) writes:
> In article <14144 at medusa.cs.purdue.edu> avr at 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