Re: Using GTK's to build transparent backgrounds

[Michael Torrie <torriem chem byu edu>]

On Sun, 2006-09-10 at 22:23 -0400, Raul Z.T. wrote:
> Hi everyone , 
>               Well after hours searching in the documentation of GTK+ 
> without luck , i finnaly decided to ask the experts . Actually im building 
> an application that displays text using Pango , i modified the background 
> collor of the drawing area without problem , but how i can give it some 
> transparency/opacity to that area? i  need it as transparent as possible , 
> my idea is to get the same effect that gives transparent rxvt's and others 
> , how i can do that? 

I believe cairo does support rendering with an alpha channel.  However,
your app will only have true window-level alpha channel on desktops that
support that, which on X11 means only when window managers that support
composite (in other words a composite manager) are used.  Right now the
KDE window manager supports composite, but most of the time it is
disabled because it conflicts with openGL acceleration (at least on
nvidia).  The newer rendering systems such as Xgl or AIXGL will work
nicely, though.

If you want to do pseudo-transparency, which is what rxvt does, you'll
need to ask the X server for the background pixmap, then clip it
appropriately and shade it and paste it as your background.

> 
> I am using perl-gtk2 (1.21)
>   Glib 1.120 
>   GTK+ -> 2.8.15-1
> 
> on fedora core 5
> 
> Many thanks in advance!
> Raul
> 
> 
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