Drags the selection view for this widget.
        
        :param      event | <QMouseMoveEvent>

def mouseMoveEvent(self, event):
        """
        Drags the selection view for this widget.
        
        :param      event | <QMouseMoveEvent>
        """
        w = event.pos().x() - self._region.x()
        h = event.pos().y() - self._region.y()
        
        self._region.setWidth(w)
        self._region.setHeight(h)
        self.repaint()
        
        super(XSnapshotWidget, self).mouseMoveEvent(event)