code: def _post_draw(self, widget, ctx):
      if self._rubberband_rect is None:
          return
  
      x0, y0, w, h = (
          dim / self.device_pixel_ratio for dim in self._rubberband_rect
      )
      x1 = x0 + w
      y1 = y0 + h
  
      # Draw the lines from x0, y0 towards x1, y1 so that the
      # dashes don't "jump" when moving the zoom box.
      ctx.move_to(x0, y0)
      ctx.line_to(x0, y1)
      ctx.move_to(x0, y0)
      ctx.line_to(x1, y0)
      ctx.move_to(x0, y1)
      ctx.line_to(x1, y1)
      ctx.move_to(x1, y0)
      ctx.line_to(x1, y1)
  
      ctx.set_antialias(1)
      ctx.set_line_width(1)
      ctx.set_dash((3, 3), 0)
      ctx.set_source_rgb(0, 0, 0)
      ctx.stroke_preserve()
  
      ctx.set_dash((3, 3), 3)
      ctx.set_source_rgb(1, 1, 1)
      ctx.stroke()
  
imports: import functools
  import logging
  import os
  from pathlib import Path
  import matplotlib
  from matplotlib import _api, backend_tools, cbook
  from matplotlib.backend_bases import ToolContainerBase, CloseEvent, KeyEvent, LocationEvent, MouseEvent, ResizeEvent
  from gi.repository import Gio, GLib, GObject, Gtk, Gdk
  from .None import _backend_gtk
  from ._backend_gtk import _BackendGTK, _FigureCanvasGTK, _FigureManagerGTK, _NavigationToolbar2GTK, TimerGTK
label_desc: Use image node_id 19 for calling the FigureCanvasGTK3 obj's underlying member method code with example usage: obj._post_draw(widget, ctx) without return types