[Qt-interest] Detecting windowOpacity support

[Dušan Saiko]

Hello all, hello to the qt-interest list from a new user.

My problem/question would be as follows:

I know how QWidget::windowOpacity() works and I know the constraint that
"under X11 you need to have a composite manager running, and the X11 
specific _NET_WM_WINDOW_OPACITY atom needs to be supported by the window 
manager you are using."

It is fine with me, just I would need to detect this situation, so I can 
open a framed window instead of having black square for the non 
composite window managers, when using frameless window 
Qt::FramelessWindowHint and Qt::WA_TranslucentBackground.

I am looking for something like 
supportsTransparency()/supportsAlphaChannel().

I am searching the internet for more than two day on this now, no luck 
so far.
Have also tried some tricks like setting the opacity, drawing opaque 
colors and then reading the values and comparing them back (in hope if 
transparency is not supported I would see that somehow), but QWidget 
behaves completely the same in both situation wheather transparency 
works or not.

Does anyone have any hint for me ?

Thanks.