How can I get a custom QCanvasItem?

[luffy27]

Is there any examples for this method? Could you offer me some links or some materials in Qt Documents?

And as the Qt's Documents say:
"QCanvasItem is not intended for direct subclassing. It is much easier to subclass one of its subclasses, e.g. QCanvasPolygonalItem (the commonest base class), QCanvasRectangle, QCanvasSprite, QCanvasEllipse or QCanvasText."
What is the difference between subclassing from QCanvasItem and from QCanvasPolygonalItem?

Thanks a lot.