If you have a QWindow set up to draw using OpenGL, and you use a QPainter to draw shapes on the current context, then there is a problem drawing polygons with a QPen style other than Qt::SolidLine.
Basically try to draw a rectangle by setting four points. The rectangle won't be solid unless you use SolidLine.
See the attached example. Expected result would like is described in this http://doc.qt.io/qt-5/qpainter.html#drawPolygon, but when DotLine used it won't be closed.