[vtkusers] vtkInteractorStyleImage

[Gib Bogle]

I'm using vtkInteractor with QVTKWidget and vtkInteractorStyleImage.  The left 
mouse button has an interesting effect.  Holding the button down and moving the 
cursor modifies the image intensity in ways that I can not easily describe.  In 
the class documentation I read that for 2D image interaction "Left Mouse button 
triggers window level events".  As far as I can see there is nothing in my code 
that is responding to mouse events, and I'm wondering where this is happening 
and exactly what is being done. Where is it documented?