code: def on_idle():
      global t, t0, frames
      t = glut.glutGet(glut.GLUT_ELAPSED_TIME)
      frames = frames + 1
      elapsed = (t - t0) / 1000.0
      if elapsed > 2.5:
          print(
              "FPS : %.2f (%d frames in %.2f second)"
              % (frames / elapsed, frames, elapsed)
          )
          t0, frames = t, 0
      glut.glutPostRedisplay()
  
imports: from vispy.gloo import gl
label_desc: Use image node_id 3 for calling a global function with example usage: on_idle() without return types