static L<Rectangle> gridOfRectangles(Rectangle r, int cols, int rows) {
  new L<Rectangle> l;
  for row to rows: {
    int y1 = r.y+(int) Math.round(r.height*(double) row/rows);
    int y2 = r.y+(int) Math.round(r.height*(double) (row+1)/rows);
    for col to cols: {
      int x1 = r.x+(int) Math.round(r.width*(double) col/cols);
      int x2 = r.x+(int) Math.round(r.width*(double) (col+1)/cols);
      l.add(new Rectangle(x1, y1, x2-x1, y2-y1));
    }
  }
  ret l;
}