code: def render_image(self, rgbobj, dst_x, dst_y):
          
          if self.surface is None:
              return
          self.logger.debug("redraw surface")
  
          # get window contents as a buffer and load it into the AGG surface
          rgb_buf = self.viewer.getwin_buffer(order=self.rgb_order,
                                              dtype=np.uint8)
          self.surface.frombytes(rgb_buf)
docs: Render the image represented by (rgbobj) at dst_x, dst_y
          in the pixel space.
          *** internal method-- do not use ***