mono/xwt — comment on commit 02f65feeca738635639bf22179e0eb0187946617
File: Xwt.WPF/Xwt.WPFBackend/CanvasBackend.cs line 56
By slluis:

Any sequence of QueueDraw() and QueueDraw(rect) is valid. So QueueRect() will clean the dirtyRects, but if QueueDraw(rect) is then called, a new rect will be added to the list, and then only that rect will be redrawn.