[vtkusers] Use MPI in my Application

[Matthias Härtel]

Hey,

i want to use mpi in my application for parallel rendering, using the 
vtkParallelRenderManager.
So i installed mpi and rebuild vtk with it. Examples work!

Now, i must integrate mpi in my application. I use QT, so my main.cpp 
create a new QApplication and starts the mainWindow. Everything else get 
started from there.
So my question is, to use mpi, i have to run the whole application with, 
for example, 4 processes, right?
With:  "mpiexec -n 4 app.exe"
But my problem is, that i only want to use for the rendering more 
processes, not for the whole program. Can i start my processes out of 
the application?
Or do i have to init mpi in my main.cpp, and let only one process create 
my MainWindow?

You see, i do not have many experience with parallel programming :)

I hope someone can help me!

Greetings
Matthias