self.children = []

        return (tl, tr, bl, br)

        self.children = (tl, tr, bl, br)
        return self.children
    def get_leaf_nodes(self, max_depth=None):
        if not self.children:
            return [self]
        if max_depth is not None and self.depth >= max_depth:
            return [self]
        result = []
        for child in self.children:
            result.extend(child.get_leaf_nodes(max_depth))
        return result

        quad = Quad(self, (0, 0, self.width, self.height), 0)
        self.error_sum = quad.error * quad.area
        self.push(quad)

        self.root = Quad(self, (0, 0, self.width, self.height), 0)
        self.error_sum = self.root.error * self.root.area
        self.push(self.root)

    def render(self, path):

    def render(self, path, max_depth=None):

        for quad in self.quads:

        for quad in self.root.get_leaf_nodes(max_depth):

    # for max_depth in range(max(depth.keys()) + 1):
    #     model.render('out%d.png' % max_depth, max_depth)