general mouse press/release events. Here, event is
        a MplEvent from matplotlib.  This routine just dispatches
        to the appropriate onLeftDown, onLeftUp, onRightDown, onRightUp....
        methods.

def __onMouseButtonEvent(self, event=None):
        """ general mouse press/release events. Here, event is
        a MplEvent from matplotlib.  This routine just dispatches
        to the appropriate onLeftDown, onLeftUp, onRightDown, onRightUp....
        methods.
        """
        if event is None:
            return
        button = event.button or 1

        handlers = {(1, 'button_press_event'):   self.onLeftDown,
                    (1, 'button_release_event'): self.onLeftUp,
                    (3, 'button_press_event'):   self.onRightDown,
                    }
        # (3,'button_release_event'): self.onRightUp}

        handle_event = handlers.get((button, event.name), None)
        if hasattr(handle_event, '__call__'):
            handle_event(event)
        event.guiEvent.Skip()