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();
}