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Clarification on QSGNode::preprocess()

  • In the QSGNode preprocess() docs it says:
    Warning: Beware of deleting nodes while they are being preprocessed. It is possible, with a small performance hit, to delete a single node during its own preprocess call. Deleting a subtree which has nodes that also use preprocessing may result in a segmentation fault. This is done for performance reasons.

    Referring to the "QtQuick scene graph docs":,

    From what I can tell, QSGNode::preprocess() is called by the render thread. Scene manipulation (addition/removal of nodes) is also done by the render thread in QQuickItem::updatePaintNode(). Where can nodes be deleted such that I'd get a segmentation fault or other bad behavior?

  • Is that a typo or are you asking how you can produce segfaults by deleting scene nodes?

  • It's not a typo. I don't understand what conditions cause seg faults when I delete scene nodes. I'm pretty confused in general on how to deal with the new scene graph stuff since there's a separate render thread asynchronously doing stuff.

    If I have some custom opengl rendering in a QSGNode in the preprocess() call, will I get a seg fault when someone changes the QQuickView to another QML file and parts of my scene graph get deleted?

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