help with QPainter::setCompositionMode()

I'm just playing around with QPainter and get the following message on the console:

QPainter::setCompositionMode(), composition modes not supported on device

whenever I use QPainter::setCompositionMode(). For example, I tried

painter.setCompositionMode(QPainter::CompositionMo de_SourceOver);

What else do I need to set up on my system. I am using Qt 4.0.1 on an X11 based linux box

You can only set the composition mode for QPainter objects that operates on a QImage.

That's not exactly true. You can use composition modes for QPainter if you have the Compositemodule enabled in your X server.

Quote:

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Originally Posted by wysota

That's not exactly true. You can use composition modes for QPainter if you have the Compositemodule enabled in your X server.

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I'm a bit of a linux idiot, would you have any ideas on how to do that?

http://gentoo-wiki.com/TIP_Xorg_X11_and_Transparency