code: def on_draw(self, event):
      gloo.clear()
      self.program.draw("triangles", self.index)
  
file_path: vispy/examples/demo/gloo/unstructured_2d.py
imports: import sys
  import numpy
  import scipy.spatial
  from vispy import gloo, app
  from vispy.util.transforms import ortho
label_desc: Use image node_id 4 for calling the Canvas obj's underlying member method code with example usage: obj.on_draw(event) without return types