Custom GL/DirectX QWidget Problems With Qt 4.4

I spent the better part of Friday trying to use Irrlicht to draw 3D scenes in a Qt widget. The code that was sent to me worked perfectly with Qt 4.3, but crashed with a landslide of errors when I compiled Qt 4.4-rc1:

Linux 2.6.18-8.1.3.el5 #1 SMP Mon Apr 30 14:15:37 EDT 2007 i686
Creating X window…
XErrorEvent: BadWindow (invalid Window parameter)
XErrorEvent: BadWindow (invalid Window parameter)
XErrorEvent: BadWindow (invalid Window parameter)
XErrorEvent: BadWindow (invalid Window parameter)
XErrorEvent: BadWindow (invalid Window parameter)
XErrorEvent: GLXBadDrawable
Could not make context current.
XErrorEvent: BadDrawable (invalid Pixmap or Window parameter)
XErrorEvent: BadWindow (invalid Window parameter)
XErrorEvent: BadDrawable (invalid Pixmap or Window parameter)
XErrorEvent: BadDrawable (invalid Pixmap or Window parameter)
Using renderer: OpenGL
Segmentation fault

The code used tried to draw to an existing QWidget by passing the window id (QWidget::winId()) to irrlicht (supported in latest SVN) and creating a context around it. However Qt 4.4 started returning invalid window id’s for some reason. After a bit of hacking, I managed to get the code working perfectly with a QGLWidget, but that had a lot of extraneous features that I did not need (they are provided by irrlicht) and compability with DirectX was in question. After a bit of investigation of the difference between QWidgets and QGLWidgets, I found the following piece of code in the constructor of QGLWidget:

setAttribute(Qt::WA_PaintOnScreen)

This attribute is supposed to allow other libraries to draw into the QWidget, but seemingly it is no longer turned on by default in Qt 4.4. So I tried to put it into the constructor of my irrlichted QWidget and everything worked!

So if you are trying to draw using an exernal library into a QWidget, make sure that WA_PaintOnScreen is turned on by placing the above mentioned code into the constructor.