(defun rects-overlap (r-tl r-br r2-tl r2-br)
  (not (or (< (x r2-br) (x r-tl))
           (< (y r2-br) (y r-tl))
           (> (x r2-tl) (x r-br))
           (> (y r2-tl) (y r-br)))))