How can I draw a selection rectangle on the screen with Qt?

How can I draw a selection rectangle on my screen with 开发者_开发百科Qt in X11? I want to be able to drag a rectangle on my screen (outside of the application) and then save the whole rectangle.

Thanks in advance.

Part of the solution will involve using the grabWindow() function of QPixmap like so:

QPixmap::grabWindow(QApplication::desktop()->winId());

Qt has an example program for this here.

There rest of the solution, drawing the area to grab, can probably be achieved by either using a full screen transparent window to render a mouse drawn rectangle and then taking the section it outlines from the grabbed desktop image or using a full screen window with the entire grabbed screen painted on it.