Zone Mode ‘zones’ Emacs out, choosing one of its random modes to obfuscate the current buffer, which can be used as a screensaver.

Try it with ‘M-x zone’.

To enable Zone Mode for all buffers after Emacs is idle for 2 minutes, add the following Lisp code to you InitFile or try it out by EvaluatingExpressions.

  (require 'zone)
  (zone-when-idle 120)

This will also enable Zone Mode after 2 minutes of idle.

  (setq zone-timer (run-with-idle-timer 120 t 'zone))

If you want to try out a particular Zone program, here is an interactive command, ‘M-x zone-choose’,

  (defun zone-choose (pgm)
    "Choose a PGM to run for `zone'."
       "Program: "
       (mapcar 'symbol-name zone-programs))))
    (let ((zone-programs (list (intern pgm))))

To make your own program, add it to ‘zone-programs’.

  (eval-after-load "zone"
    '(unless (memq 'zone-pgm-md5 (append zone-programs nil))
       (setq zone-programs
             (vconcat zone-programs [zone-pgm-md5]))))

Here’s an example Zone program that outputs lines that are the result of iteratively finding the md5 checksum of checksums. A program is typically just a function that performs various insertion and deletions within the buffer. Zone Mode operates on a copy of a buffer, so there’s no reason to operate on buffers or undo your changes. The facilities in Zone do this for you.

  (defun zone-pgm-md5 ()
    "MD5 the buffer, then recursively checksum each hash."
    (let ((prev-md5 (buffer-substring-no-properties ;; Initialize.
                     (point-min) (point-max))))
      ;; Whitespace-fill the window.
      (zone-fill-out-screen (window-width) (window-height))
      (random t)
      (goto-char (point-min))
      (while (not (input-pending-p))
        (when (eobp)
          (goto-char (point-min)))
        (while (not (eobp))
          (delete-region (point) (line-end-position))
          (let ((next-md5 (md5 prev-md5)))
            (insert next-md5)
            (setq prev-md5 next-md5))
          (forward-line 1)
          (zone-park/sit-for (point-min) 0.1)))))

With the following you can lock X11 with M-x lock-screen:

 (defun lock-screen ()
   "Lock screen using (zone) and xtrlock
 calls M-x zone on all frames and runs xtrlock"
     ;(shell-command "xtrlock &")
      (start-process "xtrlock" nil "xtrlock")
      '(lambda (process event)
     (zone-when-idle 1)))

NOTE: this depends on the program xtrlock (package ‘xtrlock’ in Debian GNU/Linux)