static Rect intersectRects(Rect a, Rect b) {

  int x = max(a.x, b.x), y = max(a.y, b.y);

  int x2 = min(a.x+a.w, b.x+b.w), y2 = min(a.y+a.h, b.y+b.h);

  ret new Rect(x, y, x2-x, y2-y);

}

static Rect intersectRects(Rect a, int x1, int y1, int w, int h) {

  if (a == null

    || a.x >= x1 && a.y >= y1 && a.x2() < x1+w && a.y2() < y1+h)

    ret a;

  ret rectFromPoints(

    max(a.x, x1), max(a.y, y1),

    min(a.x2(), x1+w), min(a.y2(), y1+h));

}