I am trying to implement a custom OpenGL scene (wrapped in a QGLWidget), but still use QT controls (such as slide bars and buttons). I tried to make my main widget a QGLWidget, which has QWidgets as children. The child widgets seem to work (when I click a pulldown menu, its options appear), but the widget fails to draw (I see a white square). I changed the base class of my children widgets from QWidget to QGLWidget, and now QPainter calls work, but QT GUI stuff is still not displaying…
Some claim that a QGLWidget can not have QWidgets as children… I am not sure about that and I’m not willing to give up. By the way, I am using Visualization Library to draw the OpenGL scene, but it is just an OpenGL wrapper…
Any clues where the problem might be? Also, key events stop being processed for some reason when I add subwidgets to the GQLWidget.
Update:
I tried various combinations of widgets and layouts. It seems that the QGLWidget just gets drawn on top of anything. I even tried with raise() to arrange Z-depth of the widgets, to no avail. Is overlayGL() the only way to draw on top of an OpenGL widget?
Update 2
After months of trying, I figured out it is something related to QT. Whenever a QGLWidget is drawn on top of another QGLWidget, the first’s background() function is not called. So a button is there and can be clicked, but it’s not drawn. My workaround was to draw everything myself using QPainter – that works. What I found curious is, one has to use QPainter::startNativePainting() in order to draw with it. One would expect that they would overload start() in QPainter to call startNativePainting() whenever a QGLWidget is the painting device…
Another (maybe useful) fact is that QPainter calls CHANGE the Opengl context. So if you have another tool in cooperation with QPainter (in my case Visualization Library), chances are that one of them will crash (in my case VL which checks if the context state has been cleared before each frame).
There is a labs example of rendering Qt widgets using opengl it’s a little old and I haven’t tried it with the improved qglwidget in 4.8
There is also an issue with drawing over the top of a fullscreen QGLwidget – it was supposedly a bug in NVidia’s openGL driver. It doesn’t seem to have been resolved
https://bugreports.qt-project.org/browse/QTBUG-7556