QQuickCanvas classes make use of QSG classes outside the rendering thread

This will result in undefined behavior!

Specifically:

• QQuickCanvasPixmap has a QSGTexture member but lives on the GUI thread and will be reference counted by the QML engine. If the QML engine outlives the scene graph, the texture will be deleted using deleteLater() which will result in either the texture leaking or if the scene graph is started up again, it will crash as the new scene graph will have a new GL context and may also not have a gl context at all when the DeferredDelete event gets delivered.
• The QQuickContext2D contains a QQuickContext2DTexture which suffers from the exact same problem.