What you are describing and the difficulties you are having in pinning
it down sound exactly like what I've encountered. In a previous
posting I reported also seeing jitters when I tried to interactively
scale an object using just a simple TransformGroup -- no fancy view
transforms or eye-to-world mappings. The problem seemed to only occur
for scale factors less than 1.0 and it seemed to affect the whole
transform even though I was only setting scale.
All the jitter problems I've observed seem to have the same sort of
jittery "quality" which makes me suspect that they are related, but
how? They also manifest themselves in slighty different ways such as
sign flipping, lagging, and just random trashing of the transform.
Hopefully someone from Sun can shed some light on these mysteries. In
the meantime it's giving me cause for concern because I need all these
features; 1.1.1 is due to come out soon; and I haven't seen the
"jitters" mentioned in the bug list.
--jon
Roger Cottam wrote:
>
> Jon,
>
> Yes, I've seen this as well with multiple views. My scenario isn't simple
> so it's hard to nail down exactly what the problem is, but multiple views
> is the key that starts the jitters. I've seen it in TransformGroup objects
> which I am modifying or have modified with a mouse drag...
>
> I also have some issues with code that uses
> Canvas3D.getCenterEyeInImagePlate(), but I can't say that I have a problem
> with that method in particular. It seems that if I use the functions for
> ray casting (generatePickRay and pickQuad) I get a VERY jittery effect on a
> TransformGroup 'above' the ViewPlatform. This happens with only one
> canvas. The idea is that when the mouse is dragged with the right button
> down I project a ray onto a plane perpendicular to the view at the location
> of the 'selected' object. Over two frames this gives me a delta to move
> the viewpoint so I can 'pan' in the view plane relative to an object. I
> print out the 3D points that I calculate on that plane each frame an
> smoothly run the mouse across the window. I get values that jump pos and
> neg and big and small, it may be that the sign is the only thing that gets
> flipped but I haven't studied the data enough to say for sure. I'm not
> sure why yet, but this 'jitter bug' may have something to do with it...
>
> If I find anything I'll let you know.
>
> Roger
>
> At 06:53 PM 3/2/99 -0800, Jon Barrilleaux wrote:
> >I think there is a problem with the J3D computation of the
> >view-to-world transformation. I've seen the problem so far in
> >Canvas3D.getCenterEyeInImagePlate(), View.getUserHeadToVworld(), and
> >and, Node.getLocalToVworld().
> >
> >What is happening is that the value returned seems to "lag" what the
> >ViewPlatform is actually doing, but its not just a simple lag. There
> >seems to be a pronounced "jitter" to it; and if the ViewPlatform stops
> >moving often the lag will remain until the view-to-world transform is
> >read a second time.
> >
> >Although this is only a guess, perhaps this is related to the problem
> >I reported last month (which no one at Sun seemed interested in)
> >concerning jitter which occurs when multiple views are used. That
> >seemed to be view related also.
> >
> >Has anyone seen similar problems with any of the view-to-world
> >transforms? (I know other people have complained about jitter in
> >multiple views.)
> >
--
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