code: def viewbox_mouse_event(self, event):
          
          # When the attached ViewBox reseives a mouse event, it is sent to the
          # camera here.
          
          self.mouse_pos = event.pos[:2]
          if event.type == 'mouse_wheel':
              # wheel rolled; adjust the magnification factor and hide the 
              # event from the superclass
              m = self.mag_target 
              m *= 1.2 ** event.delta[1]
              m = m if m > 1 else 1
              self.mag_target = m
          else:
              # send everything _except_ wheel events to the superclass
              super(MagnifyCamera, self).viewbox_mouse_event(event)
              
          # start the timer to smoothly modify the transform properties. 
          if not self.timer.running:
              self.timer.start()
          
          self._update_transform()
docs: ViewBox mouse event handler
  
          Parameters
          ----------
          event : instance of Event
              The mouse event.