code: def ms_zoom_in(self, viewer, event, data_x, data_y, msg=False):
          
          if not self.canzoom:
              return True
  
          if not (event.state == 'down'):
              return True
  
          with viewer.suppress_redraw:
              viewer.panset_xy(data_x, data_y)
  
              if self.settings.get('scroll_zoom_direct_scale', True):
                  zoom_accel = self.settings.get('scroll_zoom_acceleration', 1.0)
                  # change scale by 100%
                  amount = self._scale_adjust(2.0, 15.0, zoom_accel, max_limit=4.0)
                  self._scale_image(viewer, 0.0, amount, msg=msg)
              else:
                  viewer.zoom_in()
  
              if hasattr(viewer, 'center_cursor'):
                  viewer.center_cursor()
              if msg:
                  viewer.onscreen_message(viewer.get_scale_text(),
                                          delay=1.0)
          return True
docs: Zoom in one level by a mouse click.