Re: Recreating scene graph with VisAD


Since we never see this NullPointerException in VisAD,
I have to assume it is caused by your DisplayRendererJ3D
modifications that manipulate the Java3D scene graph. I
doubt that I can be of much help in debugging this.

Good luck,

> Thanks for the reply.  I am modifying the DisplayRendererJ3D class to
> enable us to modify the "camera" or viewer's position instead of rotating
> the object in 3D space.  Basically, we have a method that at one time
> called a ProjectionControl object to set the matrix for our object's 3D
> transformations via the setMatrix( ... ) function in ProjectionControl.  So
> I decided instead of modifying the object's rotations, it is much more
> intuitive to move the camera around the object.  Therefore, I modified the
> DisplayRenderJ3D to allow me to change the view nodes in the scene graph
> (particularly those like the view and the vpTrans) in order to move the
> camera about the scene.  This is all fine and works beautifully.
> However, there were the problems of opening multiple files as I alluded to
> in my previous email, of which I will explain further.  Essentially, we are
> writing an application in which you can have multiple files open at a time.
>  Each file is a 3D canvas in which data is rendered in 3D. When you open a
> file, and then close it, the destroy( ) function in DisplayRendererJ3D is
> called and basically wipes out only portions of the scene graph, notably
> the canvas, mouse listener, the root (the root branch group of the locale),
> the vpTrans (transform group for the view platform) and the view object
> itself.  Therefore, these objects are all set to null when the file is
> closed.  Then, when we try to open a new file, VisAd throws a null pointer
> exception, because setting up the camera requires me to have a valid handle
> to the view and the vpTransform ( which were deleted when portions of the
> last scene graph was destroyed ). Therefore, my question is, how do I keep
> the scene graph from being destroyed from one file to the next, or how do I
> get the view portions of the scene graph re-created before any geometry is
> to be rendered?
> Thanks in advance for your time.
> Greg
> Bill Hibbard writes:
> > On Wed, 17 Jul 2002, Greg Buron wrote:
> >
> > > I have a question regarding recreating the scene graph with VisAd.  I am
> > > working on an application in which an object is created and a scene graph
> > > is created (somehow) and then when that file is closed, the scene graph is
> > > destroyed.  Then, when I try to open a new file in the same application I
> > > run into a null pointer exception because in the DisplayRendererJ3D class,
> > > when the renderer tries to access the view and vpTrans transform group.
> >
> > We never see this behavior. You need to tell us what
> > VisAD methods you are calling to cause the Exception,
> > and whether you are directly manipulating the Java3D
> > scene graph by extending VisAD classes or some other
> > means.
> >
> > Bill
> >

Bill Hibbard, SSEC, 1225 W. Dayton St., Madison, WI  53706
hibbard@xxxxxxxxxxxxxxxxx  608-263-4427  fax: 608-263-6738

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