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Qt-interest Archive, February 2007
QGraphcisScene in other threads

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Greetings All-

I am having a problem getting QGrpahicsView to repaint when I
add a new QGraphics Scene.

This works fine:

QGraphicsScene *oldScene(NULL);
while (true) {
	QGraphicsScene  *newScene = new QGraphicsScene();

	// fill newScene with items.
	
	ui.view->setScene(newScene);

	if(oldScene != NULL) delete oldScene;

	oldScene = newScene;
}

The Problem:  Filling newScene with items is time consuming and
while doing so freezes the GUI.  So I moved the creation of new scenes
to a "compute thread".    In the compute thread I first create
the new scene like before, but I call moveToThread before I
send a signal to the GUI that a new scene has been created:

	QGraphicsScene  *newScene = sceneQueue->newScene();

	// fill newScene with items.

	 newScene->moveToThread(QApplication::instance()->thread());

	emit newSceneReady()


Back in the GUI thread I retrieve newScene and set it to the view.
This handoff of scenes is protected by a mutex in sceneQueue.
The GUI thread creates sceneQueue.

I can not get this new scene to display unless I cause a repaint by  
covering and
then uncovering the window or by calling view->scale(1.01,1.01).
Calls to repaint and update have no effect.

Am I doing something wrong ?

Thanks in advance for any help,
-Dennis Flanigan



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