Len Granowetter (lengrano++at++mak.com)
Mon, 10 Mar 97 15:32:56 -0500
I'm hoping that someone can shed some light on an apparent Performer
bug we've seen in our Performer-based application.
Under some circumstances, some polygons appear with the wrong
textures on them. The scene will look completely normal, then we'll
change the position of the eyepoint so that some new vehicle is in
view, or something, and suddenly, a texture from the vehicle replaces
the texture on the cloud polygon, or on some piece of the terrain.
Move the eyepoint back, and now the right texture is restored. By the
way, this problem does NOT seem to happen if lighting is disabled.
It would seem that the problem is related to the following note that
appears in the pfGeoState man page:
In some situations it may appear that pfGeoStates do inherit from each
other. This is because IRIS Performer currently does not provide any
defaults for the state attributes listed above such as PFSTATE_TEXTURE
and PFSTATE_FRONTMTL. Consequently, if the application does not
explicitly set these attributes, it is possible for pfGeoStates which
inherit these attributes to inherit them from previous pfGeoStates.
However, all of our geometry is built by the MultiGen .flt loader, and
Marcus Barnes at MultiGen assures me that:
> I'm trying to figure out though, why our scene graph would contain
> GeoStates with the texture unset.
The .flt loader always sets them exactly. They are either bound and
enabled or null'd and disabled
Marcus and others say they've seen the problem too. This is from
Marcus:
I've seen this too. I reported it to SGI a year or 2 ago as a
pfGeoState::apply() bug. Something going wrong in the push/popping.
Once, I spoke with Sharon Clay about it and she thought that it was
really a GL bug (Irix 5.3/Iris GL) and that there wasn't much
Performer could do about it. I haven't seen the problem since I've
been using Irix 6.2 myself.
I myself _have_ seen the problem under IRIX 6.2/OpenGL/Performer 2.1
as well.
Does anyone have any fixes, workarounds, etc? Or know of any patches
that solve the problem?
-Len
----------
|\ /| . . | / Len Granowetter
| \/ | _ | ( MaK Technologies
| | /-\ | \ (617) 876-8085 Ext. 121
T E C H N O L O G I E S lengrano++at++mak.com
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