[vtkusers] Occlusionquery by using Shaders

[Engel Markus]

Hi!

I'll say it right away, I am completely new to using shaders and just want to know if what I want to do is possible at all.

I'm currently doing an occlusion-test, that means I check which cells of a VTKPolyData are hidden behind other surfaces. Up to now, I've been using the GL_OcclusionQuery (openGL put into a new mapper inheriting from the VtkOpenGlPolyDatamapper or something like that  =) ) and it works ok. The problem is, that it takes very long for huge meshes with e.g 200000 cells.
Now I was wondering if this kind of calculations can be done by shaders. 
So far I only found stuff about how you create a fancy look on your surfaces.

Thanks for answering (I hope somebody does answer)

greets Markus