docstr: Use the mouse wheel to zoom.
docstr_tok: ["Use","the","mouse","wheel","to","zoom","."]
code: def on_mouse_wheel(self, event):
      """Use the mouse wheel to zoom."""
      delta = event.delta[1]
      if delta > 0:  # Zoom in
          factor = 0.9
      elif delta < 0:  # Zoom out
          factor = 1 / 0.9
      for _ in range(int(abs(delta))):
          self.zoom(factor, event.pos)
  
file_path: vispy/examples/demo/gloo/mandelbrot.py
imports: from vispy import app, gloo
label_desc: Use image node_id 8 for calling the Canvas obj's underlying member method code with example usage: obj.on_mouse_wheel(event) without return types