I'm performing a pseudo-overlay operation that involves scaling down
an object and moving it very close to the display. This involves
detecting changes in view geometry and then updating the overlay
object geometry.
Now we all know that Java 3D has problems doing such operations
because the change detection occurs in one scene graph "cycle" and any
resulting programmatic update won't be seen until the next "cycle"
(i.e. the operation always appears to be one cycle behind). However,
I've noticed something odd going on when I use a billboard together
with my pseudo-overlay object. The billboard appears to "draw" its
target object closer to the display than my object (which is only
about 0.25 units from the eye). Then, about .1 or .2 seconds later
(i.e. much longer than a frame cycle) my object appears in front of
the billboard one like it should.
This all seems most odd. I know this descriptionis a bit cryptic but
I'm really curious as to what is going on inside of Billboard? I'm
certain of the geometries involved, and my object is always in front
of the billboard one. How could the Billboard possibly "draw"
anything in front of an object that is closer to the display? Is it
doing some sort of immediate mode rendering (I don't see why it should
but that is what appears to be happening)? Why the appreciable delay
between the biillboard doing its "drawing" and my object appearing?
When my object interacts with non-Billboard objects everything is as
it should be (other than looking crappy because it is always one cycle
behind).
Any clues? Is this a bug?
--jon
____________________ Peculiar Technologies ____________________
Jon Barrilleaux 3800 Lake Shore Ave. Purveyors of
[EMAIL PROTECTED] Oakland, CA 94610 Alternate Reality
510.444.4370 voc Augmented Simulation
510.444.0231 fax www.augsim.com and 3D Solutions
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