Qt Location / Qml Maps: reduce polyline points depending on location and visible area

The MapPolyline documentation (http://doc.qt.io/qt-5/qml-qtlocation-mappolyline.html) states that lines with many points are inefficient. The number of points can be easily and dynamically adapted:

1.) Calculate the minimum visible distance in pixels for the current longitude/latitude bounding box and zoom level.
2.) If the distance between two polyline points is smaller than the visible distance then merge the points.
3.) Ommit points which lie outside the bounding box (with some additional margin).

Point 3 can be tricky but the other two work very well (I have used this with non-Qt projects).