public Rect ExpandToContain (Rect r, Rect r2) {
float xMin = Mathf.Min (r.xMin,r2.xMin);
float xMax = Mathf.Max (r.xMax,r2.xMax);
float yMin = Mathf.Min (r.yMin,r2.yMin);
float yMax = Mathf.Max (r.yMax,r2.yMax);
return Rect.MinMaxRect (xMin,yMin,xMax,yMax);
}