code: def on_draw(self, ev):
      self.context.set_clear_color((0, 0, 0, 1))
      self.context.set_viewport(0, 0, *self.physical_size)
      self.context.clear()
      for vis in self.visuals:
          vis.draw()
  
file_path: vispy/examples/basics/visuals/dynamic_polygon.py
imports: import sys
  import numpy
  from vispy import app, visuals
  from vispy.visuals import transforms
label_desc: Use image node_id 2 for calling the Canvas obj's underlying member method code with example usage: obj.on_draw(ev) without return types