//
// function to compute bounding box of two rectangles
// input, output tuples are of the form (x, y, width, height)
//
def bbox(r1 : (Int, Int, Int, Int), r2 : (Int, Int, Int, Int)) : 
    (Int, Int, Int, Int) = 
{
  val (x1, y1, w1, h1) = r1;
  val (x2, y2, w2, h2) = r2;

  val x = x1 min x2
  val y = y1 min y2
  val width = ((x1 + w1) max (x2 + w2)) - x
  val height = ((y1 + h1) max (y2 + h2)) - y

  (x, y, width, height)
}