[PD] gem - feedback & perspective

Thoralf Schulze thoralf_schulze at yahoo.de
Tue Jan 30 09:30:44 CET 2007

hi there,

i'm stuck with a problem that really drives me nuts: i
have a fairly complex 3d scene. my aim is to take a
snapshot of a part of this scene via pix_snap2tex,
render this texture on a rectangle that covers exactly
the same area where the snapshot has been taken and do
this over and over again to create trails of objects
moving over this part of the scene.
now, no matter what i do, the positions of the moving
objects and their representations in the snapshots are
always slightly off. as a result, the trails are not
what they are supposed to be - they tend to vanish in
the middle of the snapshot, instead of representing
the motion of the moving objects.
everything is perfectly fine when doing the same thing
with just a single [rectangle 5.33333 4] filling the
whole screen, so it works in principle. but i do need
to have other parts of the scene visible as well ...

i guess that OpenGL's perspective calculations are 
kicking in here - is there any way of preventing this?
i extensively played around to get this straight:
among other things, i tried [ortho], another attempt
was to make the single rectangle partly transparent
with [alpha], but none of these ideas worked.

i greatly appreciate any help -

thank you,

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