Thanks @sankhesh, I’ve done as you suggest - made a local copy of vtkInteractorStyleRubberBandPick, renamed it MyRubberBandStyle; I’ve added a class member qquickVTKItem_ that points to my QQuickVTKItem object. The errors I describe happen in MyRubberBandStyle::RedrawRubberBand(), called by MyRubberBandStyle::OnMouseMove(), i.e. both these are running in the same thread. I modified OnMouseMove() so that it queues RedrawRubberBand() to execute in the Qt-Render thread (instead of calling RedrawRubberBand() directly), by calling QQuickVTKItem::dispatch_async():
// Dispatch lambda function to redraw rubber band in Qt render thread
qquickVTKItem_->dispatch_async([this](vtkRenderWindow *renderWindow,
vtkSmartPointer<vtkObject> userData) {
this->RedrawRubberBand();
});
However this does not fix the errors, which are still emitted by RedrawRubberBand(). Debugging this, I see that RedrawRubberBand() is still running in the same thread as OnMouseMove(), despite being queued to run in the Qt-Render thread. Why is this? How can I make RedrawRubberBand() run in the Qt-render thread?