Shadow bug

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Kenneth B Russell (kbrussel++at++media.mit.edu)
Tue, 12 May 1998 23:41:14 GMT


We're using the pfLightSource mechanism on an Onyx2 with iR
graphics to generate shadows in our application. We have found
that with certain camera positions, some garbage geometry appears
to be creating a shadow; by moving the camera slightly, the
effect goes away. See http://www.media.mit.edu/~kbrussel/shadowbug.html.
The problem is extremely dependent on window size; making the
window bigger changes the position for which the bug occurs.

Angus Dorbie suggested the last time I asked this that we might
be generating wrong LODs for certain geometry; now that we've got
things integrated in our application, though, I don't think this
is the cause. First, we have a custom loader, and I know I'm not
generating any LODs; second, the effect seems to be dependent on
camera position in a fine rather than a gross sense. That is, the
bug only appears when the camera enters certain small regions of
space (and not necessarily when it's in the shadow frustum).

Has anyone seen this before? Do we need to patch our machine? It
has been a while since we installed a patch set, because the last
one we tried caused a kernel panic upon bootup, and we haven't
had the potential few days to track that problem down.

Thanks very much,

-Ken

__________________________________________________________________________
Kenneth B. Russell Synthetic Characters Group, MIT Media Lab
kbrussel++at++media.mit.edu http://www.media.mit.edu/~kbrussel
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