[vtkusers] Renders or render windows blending??? Any idea?

[vespasiano at libero.it]

Hi all,
I need to blend the output of two renders. The first render renders some 3D 
objects. The other render renders a plane where I have a texture over connected 
to a video source. Now I need to blend the output of the first render over the 
second output. Till now i use a multilayered render window where i put the 
first render on the upper layer but i can't control the alpha value. I need to 
control the alpha value of the first render output pixel to control blending 
intensity.

Somebody have any idea to resolve my problem? 

Many thanks.

Best Regards.
Ricciardi Francesco.
Università Politecnica delle Marche.