Re: does pfGetTravMat matrix include projection?

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Allan Schaffer (aschaffe++at++shark.paris.sgi.com)
Fri, 17 Feb 1995 14:20:12 +0100

On Feb 17, 1:51am, David Luebke wrote:
> Does the matrix returned by pfGetTravMat include the perspective
> transform or not? My problem is this: I have a bunch of points in
> a pre-cull callback that I want to transform into screenspace. I
> was planning to use pfGetTravMat to grab the current matrix and pump
> the vertices through with pfXformPt3, when I realized that the matrix
> probably would not include the projection into screenspace. Comments
> or suggestions? Thanks,

The matrix returned by pfGetTravMat is the model transform matrix, so
no, the projection matrix (containing your perspective transform) is
not included.

Offhand this sounds fairly difficult to do since I don't think the
CULL process has a concept of the actual projection matrix or of screen
pixels.

I don't have the man pages readily available (gasp) but perhaps there
is a way to divine the proper projection matrix given the values
you've supplied to define a pfChannel, along with the perspective
matrix definition in the back of the GL Programming Guide. Sounds
gross, hopefully someone will mention a better way. :)

This would be a piece of cake from the draw process, where you could
just call mmode(MPROJECTION); getmatrix(foo); mmode(MVIEWING).

What are you trying to do?

Allan

-- 
Allan Schaffer
Silicon Graphics
aschaffe++at++sgi.com
http://reality.sgi.com/employees/aschaffe

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