[vtkusers] Why could vtkgl::GenBuffers == NULL ?

[Oliver Kania]

In a previous post, I said that my App crashes with VTK 5.6 but not 5.2
because GenBuffers == NULL during Interactor::Render.
I found a post in the archive that says GenBuffers is NULL if the OpenGl
Version is < 1.5 and
a certain extension is not loaded.
How do I query the OpenGL version which is used by VTK and how do I change
it ?
However, my driver supports GL > 2.0, and I guess VTK does load the best
possible version.
What other reason could there be for GenBuffers == NULL ?
Is it possible to avoid usage of this function by VTK ?

Best Regards, Oliver
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