protected static void OnSpeedChanged(DependencyObject obj,
                                             DependencyPropertyChangedEventArgs args)
        {
            CarouselPanel panel = obj as CarouselPanel;

            panel.InternalSpeed = (double)args.NewValue;
        }
        protected static void OnScalePerspectiveChanged(DependencyObject obj,
                                                        DependencyPropertyChangedEventArgs args)
        {
            CarouselPanel panel = obj as CarouselPanel;

            if (panel != null)
            {
                panel.InvalidateArrange();
            }
        }