def go_to(target)
      if target == :mouse
        x = Input.mouse_pos_x - center_x
        y = Input.mouse_pos_y - center_y
      else
        x = target.x
        y = target.y
      end
      self.position = [x, y]
    end
def go_to(target)
      if target == :mouse
        x = Input.mouse_pos_x - center_x
        y = Input.mouse_pos_y - center_y
      else
        x = target.x
        y = target.y
      end
      self.position = [x, y]
    end
(  )に行く