Hi,

The attached patch adds the window (frame) opacity feature to GNU  
Emacs.  The user can control the frame opacity via a frame parameter  
'alpha'.  If you like the code, I'll start to contact major  
contributors.


Tested on:

* Emacs 23.0.60 (CVS 2008-03-13; i686-pc-linux-gnu, GTK+ Version 2.12.0)
* Ubuntu Linux 7.10
* It may not work on older X11 systems (X11R6.x)

Elisp syntax:
We can use both a floating point number (0.0-1.0) as well as an  
integer number (0-100).

(set-frame-parameter nil 'alpha 80)
(set-frame-parameter nil 'alpha 0.8)
(set-frame-parameter nil 'alpha '(<active> [<inactive>]))
(set-frame-parameter nil 'alpha '(100 70))
(set-frame-parameter nil 'alpha '(nil 70))
(set-frame-parameter nil 'alpha '(0.8 nil))
(set-frame-parameter nil 'alpha nil) ;; nil = default = opaque
(set-alpha 80)
(set-alpha 0.8)
(set-alpha '(100 0.7))
(set-alpha nil)
(setq frame-alpha-lower-limit 20)
(setq frame-alpha-lower-limit 0.2)


Contributors:

* Ryo Yoshitake (frame parameter code, x_set_frame_alpha function)
* Seiji Zenitani (x_set_alpha function)
* Meadow devel team (the original version of x_set_alpha function)
* Takashi Hiromatsu (the author of the initial version)
* Yoichi Nakayama (minor improvement to x_set_frame_alpha function)