Yeah, you must think another boring thread lost in the 1000000 threads on transparent backgrounds.
But I've spent a long time reading a lot of threads and no one is clear, simple, easy to understand for a new Qt progammer, like if there are a hundred different solutions with alpha blending, qpalette, ....
So what I want to achieve is EXACTLY that :

http://www.qtforum.org/attachment.php?attachmentid=798

and if during my program the destokp background change so does the widget.
So I don't need setWindowOpacity, I've tried all the stuff with the Palette, trying to put a blanck png pixmap on the background, nothing seems to work (or I do it bad ...)

The solution would have been that the guys form Qt put the source code for that exemple :

http://doc.trolltech.com/qq/qq16-background.html
which fit my problem but they haven't.

So anyone has an understandable solution for my problem ???