GridView Parallax - Смещение фона при скроле GridView

public MainPage()
{
    this.InitializeComponent();
    itemGridView.Loaded += itemGridView_Loaded; // наш GridView
}
void itemGridView_Loaded(object sender, RoutedEventArgs e)
{
    var scrollViewer = this.itemGridView.GetFirstDescendantOfType<ScrollViewer>();
    scrollViewer.ViewChanged += scrollViewer_ViewChanged;
}
void scrollViewer_ViewChanged(object sender, ScrollViewerViewChangedEventArgs e)
{
    var scrollViewer = this.itemGridView.GetFirstDescendantOfType<ScrollViewer>();
    var delta = (scrollViewer.HorizontalOffset / scrollViewer.ScrollableWidth) * (BackImage1.ActualWidth - scrollViewer.ViewportWidth);
    BackImage1.Margin = new Thickness(-delta, 0, 0, 0);
}