[comp.sys.sgi] Resetting lighting and retaining viewpoint

kajihara@mcnc.org (Scott "Lord of Sith" Kajihara) (11/10/90)

We have programs that switch between the orthogonal projection mode and the
perspective projection mode to view objects.  When using ortho or window, the
viewpoint is reset to looking down the z-axis.  We have the following problems
to solve:  retaining the same viewpoint when switching from ortho to
perspective to ortho projections as one case and resetting the lighting behind
the viewpoint when the viewpoint is changed as a second case.  Is there any
simple way using the defined Model/View and Projection matrices to do this?

     Thank you,

     Scott Kajihara

-- 
     Scott Akira Kajihara "Insanity is a prerequisite for physics techie-types"
mcnc!kajihara  kajihara@mcnc.org  mcnc!{pyvax|pymvjb|pysgjb}!kajihara
kajihara@{pyvax|pymvjb|pysgjb}.nscu.edu kajihara@ncsuphys.BITNET
_et al._ of which I am not aware.

karron@KARRON.MED.NYU.EDU (11/11/90)

The ortho call does a hidden translation of the eye position. I
was thinking of this problem, and the solution to my mind is to
make a wrapper for the ortho call to eliminate the translation effect.

This would be by instead of defining a viewing RECTANGLE, force it to be a
viewing CUBE, and specify a height and width, not a left and right clipper,
etc.

I don't know how you would correct for a non square window. I would have to
think about that for a few more seconds before I made a better suggestion.

Please post your solution, as I do want to be able to switch transforms
for these reasons: While a perspective transform looks better, an ortho
is much better for sighting things along lines and taking measurements.

I also have a better winopen() call idea, and when I get all of this working
nicely, I will post it.

dan.
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