'update offset of childrens and return the extents of the box'

def get_extent_offsets(self, renderer):

    dpicor = renderer.points_to_pixels(1.0)
    pad = (self.pad * dpicor)
    (w, h, xd, yd) = self._children[0].get_extent(renderer)
    return ((w + (2 * pad)), (h + (2 * pad)), (xd + pad), (yd + pad), [(0, 0)])
