Transparent top-level window

[wysota]

It can be done only if the underlying system supports it and the code is heavily OS release dependent - you need different code not only on X11 and Win32, but probably also on Vista and XP or 2k. On earlier Windows systems it can't be done at all (at least without some dirty hacks). I'm sure eventually we'll get support for that in Qt, but I wouldn't bet any money it will be any time soon.