transparent emacs

It may not be so useful, but emacs23 allows you to manipulate the transparency of your emacs frames (windows). If you use Windows or X with a compositing window manager on X, you can make your windows transparent. Examples of compositing window managers are Compiz/Beryl and even the good-old Metacity (gconftool-2 -s '/apps/metacity/general/compositing_manager' --type bool true).

The following code for your .emacs makes it easy to set transparency from within emacs:

(defun djcb-opacity-modify (&optional dec)
  "modify the transparency of the emacs frame; if DEC is t,
    decrease the transparency, otherwise increase it in 10%-steps"
  (let* ((alpha-or-nil (frame-parameter nil 'alpha)) ; nil before setting
          (oldalpha (if alpha-or-nil alpha-or-nil 100))
          (newalpha (if dec (- oldalpha 10) (+ oldalpha 10))))
    (when (and (>= newalpha frame-alpha-lower-limit) (<= newalpha 100))
      (modify-frame-parameters nil (list (cons 'alpha newalpha))))))

 ;; C-8 will increase opacity (== decrease transparency)
 ;; C-9 will decrease opacity (== increase transparency
 ;; C-0 will returns the state to normal
(global-set-key (kbd "C-8") '(lambda()(interactive)(djcb-opacity-modify)))
(global-set-key (kbd "C-9") '(lambda()(interactive)(djcb-opacity-modify t)))
(global-set-key (kbd "C-0") '(lambda()(interactive)
                               (modify-frame-parameters nil `((alpha . 100)))))

Now, you can make make emacs more transparent (less opaque) by pressing C-9, while C-8 has the opposite effect. C-0 brings us back to normality.

Admittedly, window transparency is a classical solution-looking-for-a-problem. But let that not stop us from using it -- now we can watch full-screen movies while still using emacs. That, my friends, is progress.