Re: Shadow bug
Angus Dorbie (dorbie++at++sgi.com)
Tue, 12 May 1998 17:44:01 -0700
Kenneth B Russell wrote:
>
> 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,
>
Have you looked at what you are drawing to the shadow map channel?
Try checking this to see if there is anything undesirable appearing
there.
depth buffer clearing is also important. Are there any transparent
polygons in the scene which might be causing the occultation in the
depth buffer image?
Cheers,Angus.
--
"Only the mediocre are always at their best." -- Jean Giraudoux
For advanced 3D graphics Performer + OpenGL based examples and tutors:
http://www.dorbie.com/
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on Mon Aug 10 1998 - 17:57:23 PDT