public Window1()
{
    InitializeComponent();
    var transform = new TranslateTransform();
    Background = new DrawingBrush()
    {
        TileMode = TileMode.Tile,
        DestinationRect = new RelativeRect(0, 0, 15, 15, RelativeUnit.Absolute),
        Drawing = new GeometryDrawing()
        {
            Geometry = Geometry.Parse("M0,0 L0,1 0.03,1 0.03,0.03 1,0.03 1,0 Z"), Brush = Brushes.Red
        },
        Transform = transform
    };
    DispatcherTimer.Run(() =>
    {
        transform.Y++;
        return true;
    }, TimeSpan.FromMilliseconds(32));
}