private static void OnPositionPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            TimeLineHeader header = (TimeLineHeader)d;

            header.Offset = header.Position - header.ViewPort.Divide(2);
            header.InvalidateVisual();
        }
        private static void OnMarkerPositionChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            TimeLineHeader header = (TimeLineHeader)d;

            header.RecheckMarker();
            header.InvalidateVisual();
        }