Qt5 QGraphicsView and OpenGL

flyncode

Hi everybody!

Qt Version: 5.3 (OpenGL)
Platform: Windows 7 Pro x64

I want to use the QGraphicsView object to composite QWidgets over an OpenGL scene. From what I've read in the documentation, I believe this is the simplest program I could write to achieve that:

@
class CustomGL : public QGLWidget {
protected:
virtual void initializeGL() {}

virtual void resizeGL(int w, int h) {
glViewport(0, 0, w, h);
glClearColor(0.0f, 0.0f, 0.5f, 1.0f);
}

virtual void paintGL() {
glClear(GL_COLOR_BUFFER_BIT);
}
};

int main(int argc, char *argv[]) {
QApplication a(argc, argv);

QGraphicsScene* pScene = new QGraphicsScene();
pScene->addLine(0, 0, 400, 400, QPen(QBrush(Qt::green), 5));

QGraphicsView* pView = new QGraphicsView();
pView->setViewport(new CustomGL());
pView->setScene(pScene);
pView->show();
return a.exec();
}
@

I would expect a blue background (due to the glClearColor() and glClear() calls) with a green line in the foreground. However, when I run this I get a white background; it does not appear the QGLWidget is visible.

Next I thought that I would have to subclass QGraphicsScene and draw the from the drawBackground() method, like so:

@
class CustomGL : public QGLWidget
{
public:
void paint() {
paintGL();
}
protected:
// Same initializeGL(), resizeGL(), and paintGL() as above
};

class GLScene : public QGraphicsScene
{
public:
GLScene(CustomGL* pGL) : _pGL(pGL) {}

protected:
virtual void drawBackground(QPainter* painter, const QRect& rect) {
_pGL->paint();
}

private:
CustomGL* _pGL;
};

int main(int argc, char *argv[]) {
QApplication a(argc, argv);

GLScene* pScene = new GLScene(new CustomGL());
pScene->addLine(0, 0, 400, 400, QPen(QBrush(Qt::green), 5));

QGraphicsView* pView = new QGraphicsView();
pView->setViewport(new CustomGL());
pView->setScene(pScene);
pView->show();
return a.exec();
}
@

This also fails to produce the expected result; GLScene::drawBackground() is never hit.

In fact, using this "example code":http://doc.qt.digia.com/qq/qq26-openglcanvas.html, I get the same issue: a white background where the OpenGL scene is suppose to be.

Can anyone shed some light on this? Is this a Qt4 vs. Qt5 issue?

Thank you,

--Chris