Is there a chance to set an alpha-mask using XOrg?

[Leif Bergerhoff]

Peter Harris wrote:
> It depends on your toolkit. If you're not using any particular toolkit,
> the easiest way is to set _NET_WM_WINDOW_OPACITY on your window. See
> http://webcvs.freedesktop.org/xapps/transset/transSet.c?view=markup for
> an example.
>
> Make sure a composite manager is running (many desktops run one by
> default these days).

No, I don't want to make use of a toolkit if possible.

As I can see I would have to make use of the composite extension.
If I remember correctly, I read about this extension supporting max. 2 output 
devices. Right?
This would mean, I'll need another way for setting an image as an alpha-mask, 
since I want to make use of 6 output devices.

Leif