static L<Rect> mergeOverlappingRects(L<Rect> boxes) {
  while true {
    ping();
    bool change;
    for (box1 : boxes) {
      for (box2 : boxes) {
        if (box1 == box2) continue;
        if (rectsOverlap(box1, box2)) {
          //printVars("Merging", +box1, +box2);
          copyRect(rectUnion(box1, box2), box1);
          box2.w = 0;
          box2.h = 0;
          set change;
        };
      }
    }
    
    if (!change) break;
    boxes = filter(boxes, b -> nempty(b));
  }
  ret boxes;
}