QQuick + OpenSceneGraph flickering - qtquick2

Question

I am using QQuickControls 2 (SwipeView) with OpenSceneGraph for the 3d rendering. Using QQuickFramebufferObject for the integration.
Since I have introduced a SwipeView, I observe some flickering of my GUI.
I have looked for ages in the doc (it probably sums literally up to weeks) and have absolutely no idea why I have this flickering.
Here is a video of the faulty behavior (flickering starts at ~20s).
And here is my rendering code:
class OsgRenderer : public QQuickFramebufferObject::Renderer
{
public:
explicit OsgRenderer();
QOpenGLFramebufferObject *createFramebufferObject(const QSize &size) LC_OVERRIDE;
void synchronize(QQuickFramebufferObject* item) LC_OVERRIDE;
void render() LC_OVERRIDE;
protected:
friend class OsgWindow;
OsgItem* m_osgItem;
};
void OsgRenderer::render()
{
assert(m_osgItem);
if ( !m_osgItem->getViewer() )
return;
// Without this line the model is not displayed in the second
// and subsequent frames.
QOpenGLContext::currentContext()->functions()->glUseProgram(0);
// Ask OSG to render.
m_osgItem->getViewer()->frame(); // WARNING: non-blocking (executed in a thread of its own - in a thread-safe way).
// Reset OpenGl state for QtQuick.
m_osgItem->window()->resetOpenGLState();
}
Any idea of where that can come from?

Answer 1

In general it's not a good idea to have QtQuick and OSG both render to the same OpenGL context.
OSG it's keeping its GL state internally between frames, but Qt might modify it from "outside" without notifying osg, and this might cause rendering issues.
A more solid approach is have them use separate (and shared) GL context, and copy the context of the fbo osg redners to in a texture used by Qt.
I've successfully implemented this approach here: https://github.com/rickyviking/qmlosg
but haven't tested it with recent versions of QtQuick.
A more up-to-date integration can be found here: https://github.com/podsvirov/osgqtquick