'get the bounding box in display space.'

def get_window_extent(self, renderer):

    self._update_offset_func(renderer)
    (w, h, xd, yd) = self.get_extent(renderer)
    (ox, oy) = self.get_offset(w, h, xd, yd, renderer)
    return Bbox.from_bounds((ox - xd), (oy - yd), w, h)
