private void InitComposition()
{
// Get our Compositor as well as the ScrollViewer that corresponds to
// to our ListView. Then get the CompositionPropertySet that corresponds
// to the ScrollViewer.
var compositor = ElementCompositionPreview.GetElementVisual(this).Compositor;
var scrollViewer = MainListView.GetChildOfType <ScrollViewer>();
var scrollerPropertySet = ElementCompositionPreview.GetScrollViewerManipulationPropertySet(scrollViewer);
// Construct our parallax expression using the property set we got from the
// ScrollViewer. Also we make sure to clamp the result so that the image doesn't
// go off the screen/window.
var expression = compositor.CreateExpressionAnimation("Clamp(scroller.Translation.Y * parallaxFactor, -608, 999)");
expression.SetScalarParameter("parallaxFactor", 0.3f);
expression.SetReferenceParameter("scroller", scrollerPropertySet);
// Assign our expression to the visual that represents our BackgroundImage.
var backgroundVisual = ElementCompositionPreview.GetElementVisual(BackgroundImage);
backgroundVisual.StartAnimation("Offset.Y", expression);
// Get the visual that represents our HeaderTextBlock and also set up part
// of our expression.
var textVisual = ElementCompositionPreview.GetElementVisual(HeaderTextBlock);
String progress = "Clamp(visual.Offset.Y / -100.0, 0.0, 1.0)";
// Create the expression and add in our progress string.
var textExpression = compositor.CreateExpressionAnimation("Lerp(Vector3(0, 200, 0), Vector3(0, 0, 0), " + progress + ")");
textExpression.SetReferenceParameter("visual", backgroundVisual);
// Assign our expression to the text visual.
textVisual.StartAnimation("Offset", textExpression);
}
