Custom window shape using QtQuick (input events should pass through out of the shape)

I would like to create a custom shaped window (non-rectangular) using QtQuick. Out of the custom shape I would like to let input events pass through out of the (non-rectangular) shape.

What is the best way to achieve this?

Additional notes : 
Originally I am using QQuickView but I can modify the hierarchy of my QML window.
So far I tried : 
1.: to use `QQuickWidget` and its `setMask` ( https://doc.qt.io/qt-5/qwidget.html#setMask-1 ) function of it
The result : it ignores the input events partially. By partially I mean : my window does not react to clicks that are outside of the region passed to `setMask` but the click event does not interact with the contents behind my window (like eg.: Qt::WindowTransparentForInput does).
2.: and some other solutions as well. Nothing worked perfectly so far.