def circle_bbox(radius, center):
    """
    Computes the bounding box (upper-left, bottom-right) of a circle
    :param radius: radius of the circle
    :param center: (x,y) 2-tuple
    :return: list of 2 points representing the bounding box
    """
    x, y = center
    return [[x-radius, y-radius],
            [x+radius, y+radius]]