[vtkusers] on & off screen render window + parallel compositing + interaction

[Michael Bonner]

Hello vtk users,

I have a relatively simple mpi application in which every process has an 
offscreen render window, renWin (vtkXOpenGLRenderWindow w/ 
SetOffScreenRendering(1) called), but the root process has an additional 
render window that is on screen, rootWin (also vtkXOpenGLRenderWindow).

I have added a vtkCommand object as an observer for my 
vtkRenderWindowInteractor on the root process, its execute method calls a 
parallel composite function and I then... well right now I do nothing... 
because after this method is called, which includes a renWin->Render call, 
the interaction stops. To be more specific the window does not get updated 
at all anymore.

I have turned on debugging for both render windows, and periodically called 
Print, nothing appears to have changed in either.

I have turned on debugging in the vtkRenderWindowInteractor and it appears 
that, even though the window is not changing, that the interactor and style 
are behaving correctly. Additionally, I am sending the root process's 
camera information to all other process and it the info has changed 
according to the mouse movements, also snapshots of composites created 
reflect the interaction.

I have removed everything from the vtkCommand->Execute that I have 
implemented, and the one function that stops the rootWin window from 
changing is the call to renWin->Render.

I do not know why.

If anyone has any idea as to why, I would greatly appreciate any feedback. 
I am beginning to work on a toy program that will hopefully exhibit the 
same behavior.

Thanks for your time
Mike Bonner