void QGraphicsScene::addItem(QGraphicsItem * item)
Adds or moves the item and all its childen to this scene. This scene takes ownership of the item.
If the item is visible (i.e., QGraphicsItem::isVisible() returns true), QGraphicsScene will emit changed() once control goes back to the event loop.
If the item is already in a different scene, it will first be removed from its old scene, and then added to this scene as a top-level.