[vtkusers] Access style class member variables in a callback?

[David Doria]

I've added an observer to a rubberband2d style:

 //setup 2D interaction style
  vtkInteractorStyleRubberBand2D* style = vtkInteractorStyleRubberBand2D::New();
  style->AddObserver(vtkCommand::SelectionChangedEvent,SelectionChangedCallback);

  //setup render window interactor
  vtkRenderWindowInteractor* RenderWindowInteractor =
vtkRenderWindowInteractor::New();
  RenderWindowInteractor->SetInteractorStyle( style );

Now in the callback, I want to access the style's StartPosition variable:

void SelectionChangedCallbackFunction(vtkObject* caller, long unsigned
int eventId, void* clientData, void* callData)
{

  vtkstd::cout << "Selection changed callback" << vtkstd::endl;
  //vtkstd::cout << "Start: " << this->StartPosition[0] << " " <<
this->StartPosition[1] << vtkstd::endl; //can't use 'this' in
non-member function
}

Since this callback is not a member function of the style class, the
variable is not accessible. This should be very easy - as I'd imagine
the whole idea of this style is to get the StartPosition and
EndPosition of the selection?

Any suggestions/comments?

Thanks,

David