Create translucent widget on Linux without Compiz.

[TIT]

The documentation for windowOpacity-prop said:

Note 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.

That is, the opportunity to make a widget translucent only if the costs compositing manager (Compiz, for example).
How can I get around this restriction without damaging its cross-platform program?

Actually, we need not so much a translucent widget as the possibility of selection on the screen.
For example, in Linux there is a program scrot which is able to select areas on the screen and then do a screen shot selection.
A similar possibility of making the screen I want to get into their program.

p. s.: I apologize for my bad English. I translated your question using the Google Translate Tools. If something in my question is not clear (not translated correctly), then point to it and I will clarify this point.

[wysota]

You can use QDesktopWidget. Use QPixmap::grabWidget() to grab the screenshot of the desktop so that you can do selections on it.