Clarification on QSGNode::preprocess()

? Offline

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":http://doc-snapshot.qt-project.org/qt5-dev/qtquick/qtquick-visualcanvas-scenegraph.html,

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?

melghawi

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

? Offline

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?