[Really solved now!] Can not draw with OpenGL on QGLWidget
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When a QGLWidget is set as the viewport of a QGraphicsView, the painting occurs through the QGraphicsView and does not call QGLWidget::paintGL(). Use the QGraphicsView::drawBackground() and QGraphicsView::drawForeground() methods instead. (Note: OpenGL calls will need to be between QPainter::beginNativePainting ()/endNativePainting() calls).
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No, I can not draw neither from drawBackground nor from drawForeground because I know nothing about second QLWidget (I even do not know about its existance).
Suppose I develop a library, with class TFancyTabWidget, which can display arbitrary pages and
1)I want to use some 2d effects (shadows, blur and so on) => I should use QGraphics* stuff,
2)I want to various FAST animations => I should use QGLWidget as viewport. I tried use simple QWidget but in this case animations became not animations and 1-2 frames :)
3)As TFancyTabWidget developer I know NOTHING about pages, that I will display - it may be simple QWidget, or QWidget with QGLWidget as child, or QGLWidget...
3)As TFancyTabWidget developer I also want that me class works fine.PS I updated sources for better understanding of structure and relations, please use attachment New_TwoGlWidgetsBug.tar.gz from "http://bugreports.qt.nokia.com/browse/QTBUG-18813":http://bugreports.qt.nokia.com/browse/QTBUG-18813
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QGraphicsScene::addWidget() creates a QGraphicsProxyWidget which does not support widgets which draw directly onto the screen, like a QGLWidget. (See http://doc.qt.nokia.com/4.7/qgraphicsproxywidget.html#setWidget)
You'll have to restrict the arbitrary pages to QGraphicsItems and QWidgets. Since the QGraphicsView is setting the viewport to a QGLWidget, derivatives of QGraphicsItems and QWidgets can use OpenGL in their painting functions if properly surrounded by QPainter::beginNativePainting ()/endNativePainting() calls.
Note the warning in the "QGraphicsProxyWidget documentation":http://doc.qt.nokia.com/4.7/qgraphicsproxywidget.html#details which states that it "is provided for convenience when bridging QWidgets and QGraphicsItems, it should not be used for high-performance scenarios."