VTK Mouse Drag Implementation


I am developing in python and want to implement a custom mouse drag implementation. When moving the mouse I want the clicked actor to move as well (I know how to do this).

I also know how to fire the mouse move event :render_window_interactor.AddObserver(vtk.vtkCommand.MouseMoveEvent, lambda obj, ev: mouse_move(obj, ev))

The challenge is now: How do I know, inside the mouse_move function, if the left mouse button is pressed and released while the mouse moves ?

Thanks for your help