[vtkusers] pipeline setups, multiple inputs

[tom fogal]

I wrote a function that takes a vtkRenderWindow* (and a bunch of data)
and generates a StreamLine from it. It also creates a PolyDataMapper,
Renderer, and Actor, and adds them to the render window so that it can
actually project the StreamLine to the viewing area.

The problem is that if I call the function more than once I just get an
empty window.

Perhaps I can not associate multiple Renderers with the same
RenderWindow? Can I associate multiple Actors with the same Renderer,
perhaps?

Any clues / hints on what I did wrong, or ideas on how to better
structure the above in terms of VTK?

Thanks,

-tom