Getting the screen coordinate of the top left corner of a QWidget

[blooglet]

I'm making a virtual environment with Qt's OpenGL widget and I want to be able to "trap" the mouse in the center of the widget. My idea was to do this:

QPointF widgetPos = mapToGlobal(pos());
QCursor::setPos(widgetPos.x() + width()/2, widgetPos.y() + height()/2);

QPointF widgetPos = mapToGlobal(pos());
QCursor::setPos(widgetPos.x() + width()/2, widgetPos.y() + height()/2);

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However, widgetPos doesn't contain the top left corner of the screen as I would have hoped, so the cursor gets locked at the wrong position. Am I going about this the wrong way?