[vtkusers] Stereo rendering for some renderers

[Oskar Kirmis]

Hi there,

it took some time to test everything you suggested as I didn't have much 
time for it. It turns out that stereo rendering is disabled using the 
methods mentioned here, but I ran into some other strange, 
stereo-related problems in rendering. When I now render any 2D objects 
with stereo enabled in the render window but disabled in the camera, the 
first object has is rendered in stereo. Once I add a 3D poly data object 
to the renderer, everything is fine and the 2D object is rendered 
non-stereo. When I then remove the 3D object, the problem appears again.

I don't know how vtk works internally but for me it seems like clearing 
a property is missing. Any hints?

Oskar