code: def _post_draw(self, widget, ctx):
      if self._rubberband_rect is None:
          return
  
      lw = 1
      dash = 3
      if not self._context_is_scaled:
          x0, y0, w, h = (
              dim / self.device_pixel_ratio
              for dim in self._rubberband_rect
          )
      else:
          x0, y0, w, h = self._rubberband_rect
          lw *= self.device_pixel_ratio
          dash *= self.device_pixel_ratio
      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(lw)
      ctx.set_dash((dash, dash), 0)
      ctx.set_source_rgb(0, 0, 0)
      ctx.stroke_preserve()
  
      ctx.set_dash((dash, dash), dash)
      ctx.set_source_rgb(1, 1, 1)
      ctx.stroke()
  
imports: import functools
  import io
  import os
  import matplotlib
  from matplotlib import _api, backend_tools, cbook
  from matplotlib.backend_bases import ToolContainerBase, KeyEvent, LocationEvent, MouseEvent, ResizeEvent, CloseEvent
  from gi.repository import Gio, GLib, Gtk, Gdk, GdkPixbuf
  from .None import _backend_gtk
  from ._backend_gtk import _BackendGTK, _FigureCanvasGTK, _FigureManagerGTK, _NavigationToolbar2GTK, TimerGTK
label_desc: Use image node_id 19 for calling the FigureCanvasGTK4 obj's underlying member method code with example usage: obj._post_draw(widget, ctx) without return types