QQuickWindow : Center contentItem

[dvdk]

I am trying to fit the contentItem() in a QQuickWindow, like the fitInView function from QGraphicsView.

Scaling the contentItem()->childrenRect() to QQuickWindow::width() and height() is no problem, but centering the content in the QQuickWindow seems more difficult.

I fail to understand how to convert QQuickWindow coordinates to scene coordinates (mapToView equivalent)
Basically if I can determine the center of the QQuickWindow in scene coordinates, I can re-position the contentItem to be centered in the window.

What is the best way to center the contentItem in a QQuickWindow ?