[vtkusers] Partial transparency of an actor

[Baris Yalcin]

Hi everyone,
 
I want to implement that a part of an actor is completely transparent. That 
means that a part of the actor is visible and the other part invisible. 
Example:  a chair is an actor; one leg of the chair should be invisible and 
the other three legs visible. 
The transparency of the different parts of the actor is set in a lookup 
table( 0.0=invisible,  1.0=visible).
 
The problem: the transparent part is not really transparent. Non-transparent 
triangles which are occluded by fully transparent triangles are not rendered 
anymore. Instead only the background is visible in these parts of the 
visualisation.

Is it possible to organize the rendering process in a way that non-transparent 
triangles are rendered before transparent triangles? 

If somebody has any suggestions or ideas, that would be great. 
 
Thanks a lot in advance,

Baris

P.S.: in my case the rendered object is not chair, but a complex structure 
(vessel tree)