(defun ctwm-restart (frame)
  (let ((pos (frame-position frame)))
    (when (and (not (eq (frame-parameter frame 'fullscreen) 'fullboth))
	       (< (car pos) 0) (< (cdr pos) 0)
	       (>= (frame-outer-width frame) (display-pixel-width))
	       (>= (frame-outer-height frame) (display-pixel-height)))
      (set-frame-parameter frame 'fullscreen nil)
      (modify-frame-parameters
       frame `((width . ,(display-pixel-width))
	       (height . ,(display-pixel-height))))
      (toggle-frame-fullscreen))))

(add-hook 'window-size-change-functions 'ctwm-restart)