If you make the polygon, polyline or circle items in mapViewer draggable, then they scissor if dragged on/off screen

Add a mouseArea to the above item's QML files, and set drag.target:parent to make the item draggable.
Create an item in the mapviewer and drag to the side of the screen so it is partially overlapping. Then drag back onto the screen and the part that was off-screen is still scissored until you release the mouse button.