Eric Webster (ewebster@spawar.navy.mil)
Thu, 4 Mar 1999 15:21:24 -0800
I started with the perfvol demo code that ships with
Volumizer. Unfortunately, the system that I am
developing on does not have the IFL development option,
so I am unable to compile the code as is.
Thanks to a suggestion from Robert Grzeszczuk [rg@hoek.engr.sgi.com]
I replaced the IFL code in the perfvol code with the
Raw Image I/O routines found in the woglRaw OpenGL example.
Although this restricts me to using raw image files,
I am able to compile and execute the (modified) perfvol demo.
I then introduced a surface geometry node into the scene.
I loaded the x29.sv object and placed it under its own DCS
which I then placed under the "scene dcs" used for the
trackball transformer.
At first the volume wasn't "hiding" the x29, when
the x29 was behind the volume. After checking the
documentation and the code, I realized that I had added the
x29 to the scene after the volume, resulting in the volume
being drawn first. After switching the order of the two
objects, the scene was drawn correctly--with the translucent
volume partially obscuring the x29 when the x29 was behind
the volume.
But then I came upon a strange effect when the x29 left the
field of view. At the instant that the center-point of
the x29 leaves the view, the volume (and its associated
tetra box and brick box outlines) vanish. As I move
the x29 further out of the view, the volume remains
undrawn until the entire boundingsphere of the x29 is
out of view, at which point the volume and the outlines
reappear. Then, if I move the x29 back toward the view,
the volume disappears when the x29 boundingsphere re-enters
the view, and then the volume reappears when the center-point
of the x29 gets back into view. It seems as if having
the x29 partially out of view is causing the volume node
to be culled.
I then tried several modifications to see what might
be causing this behavior:
- First I removed the line
shared->chan->setTravMode(PFTRAVCULL, PFCULL_VIEW|PFCULL_GSET);
from main.cxx of perfvol.
- Next I tried changing the transformer to
FLY mode and removing the top level DCS node.
With this I first tried placing the x29 DCS and the
volume object under a root pfGroup, which I then added
to the scene. I also tried adding the x29 DCS and
the volume object directly to the scene (without
an intervening pfGroup).
- I then tried adding additional copies of x29.sv,
each under its own DCS.
None of these modifications eliminated the behavior of
the culling of the volume object. However, when I added
multiple x29 objects, I discovered that it was the position
of the "last" x29 that affected the culling of the volume.
(That is, the other geometries can be partially out of
view without affect the volume. Only when the "last" x29
node (that was added to the scene just prior to adding
the volume) goes partially out of view does the volume
suddenly get culled.
Perhaps there is some "normal" Performer behavior that is
going on here that I am not aware of. Or perhaps my code
additions to perfvol is doing something that shouldn't
be done. Or perhaps this is some sort of bug. Regardless, I
am wondering if others have observed this behavior, and, if
so, if there is a solution. (Of course, I realize that
the solution may be to "fix my buggy code." :)
I have not attached my code to this email, but if someone
desires to see it, I can supply it.
Thanks,
Eric Webster (ewebster@spawar.navy.mil)
SPAWARSYSCEN, San Diego
This archive was generated by hypermail 2.0b2 on Mon Nov 01 1999 - 12:03:15 PST