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From: Ferreira@agames.com (Carl Ferreira)
Subject: How to use perspective to clip?
Message-ID: <1994Nov21.145637.9923@dms.agames.com>
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I have heard that a perspective transformation can be used to clip to
the visible area.  If the viewing fustrum looks like this (top view):
       \          /
        \        /
    -----\------/-----
          \    /
           \  /
            \/

Then the world can be transformed so that the fustrum is effectively
this:
     |            |
     |            |
 ----|------------|----
     |            |
     |            |
     |            |

which allows the world to be clipped using simple plane equations
rather than complex.

Can anyone tell me if this is possible, and if so, how to do it?  Does
this demand that two transformations are performed, one for clipping
and one for projection?

All help is appreciated!

Carl Ferreira
