code: def _render_picking(self, **kwargs):
          
          try:
              self._scene.picking = True
              img = self.render(bgcolor=(0, 0, 0, 0), **kwargs)
          finally:
              self._scene.picking = False
          img = img.astype('int32') * [2**0, 2**8, 2**16, 2**24]
          id_ = img.sum(axis=2).astype('int32')
          return id_
docs: Render the scene in picking mode, returning a 2D array of visual 
          IDs.