From: Dirk Scheffter (scheff++at++appss.de)
Date: 06/04/2003 04:16:46
Hi Sandeep,
eyepoint should be left at position (0, 0, 0) for view frustum
calculation. Instead, you vary the left, right, bottom, top values.
(May be, near and far, also.)
(This doesn't mean that you cannot move your channel using
setView/setViewOffset.)
I remember that we used such things when we implemented viewing frustums
for a CAVE (TM) a few years ago.
We measured position of head (eyes) with a tracker as usual,
set it in relation to projection screens,
and applied then the necessary view frustum to yield a suitable
viewing pyramid which, of course, is mostly asymmetric.
It seems a little bit tricky but actually simple mathematics is all you
need. (Theorem on intersecting lines.) ;-)
Another fact is the order of makePersp and setNearFar.
man pfFrustum says: (man pfChannel directs to pfFrustum for this.)
"""
pfFrustum::makePersp is dependent on the current near plane distance.
However, subsequent changes to the near plane distance with
pfFrustum::setNearFar do not affect the field of view, simplifying clip
plane modification.
"""
If I understood it right you have to call setNearFar before makePersp
to be sure to incorporate the correct values for near and far.
(This were important for us because near appeared in our computation of
viewing frustum.)
Hope this helps a little bit.
Best regards,
Dirk.
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Dirk Scheffter
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