Limiting the mouse boundary

I'm running Linux with XFree86 4.2.0

I often use the ctrl+alt+(Pad+) and ctrl-alt-(Pad-) to zoom in
on low-res applications (Old games, usually). But I would like
to prevent the ViewPort from changing positions while I'm zoomed
in. Since the ViewPort follows the mouse movement, the simplest
solution seems to require somehow trapping the mouse within a
specified area, which would correspond to the coordinates of the
window I'm working in.

Any ideas would be appreciated.



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