private void InitializeComposition()
{
var starsVisual = ElementCompositionPreview.GetElementVisual(ForegroundStars);
var size = new Vector2((float)ForegroundStars.ActualWidth, (float)ForegroundStars.ActualHeight);
starsVisual.Size = size;
ForegroundStarsClip = starsVisual.Compositor.CreateInsetClip(0, 0, 0.1f, 0.5f);
starsVisual.Clip = ForegroundStarsClip;
}
/// <summary>
/// Create an ExpressionNode reference to this CompositionObject.
/// </summary>
/// <param name="compObj">The comp object.</param>
/// <returns>InsetClipReferenceNode.</returns>
public static InsetClipReferenceNode GetReference(this InsetClip compObj)
{
return(new InsetClipReferenceNode(null, compObj));
}
internal InsetClipReferenceNode(string paramName, InsetClip ic = null) : base(paramName, ic)
{
}
/// <summary>
/// Uses Composition API to get the UIElement and sets an ExpressionAnimation
/// The ExpressionAnimation uses the height of the UIElement to calculate an opacity value
/// for the Header as it is scrolling off-screen. The opacity reaches 0 when the Header
/// is entirely scrolled off.
/// </summary>
/// <returns><c>true</c> if the assignment was successful; otherwise, <c>false</c>.</returns>
private bool AssignAnimation()
{
StopAnimation();
if (AssociatedObject == null)
{
return(false);
}
if (_scrollViewer == null)
{
_scrollViewer = AssociatedObject as ScrollViewer ?? AssociatedObject.FindDescendant <ScrollViewer>();
}
if (_scrollViewer == null)
{
return(false);
}
var listView = AssociatedObject as ListViewBase ?? AssociatedObject.FindDescendant <ListViewBase>();
if (listView != null && listView.ItemsPanelRoot != null)
{
Canvas.SetZIndex(listView.ItemsPanelRoot, -1);
}
if (_scrollProperties == null)
{
_scrollProperties = ElementCompositionPreview.GetScrollViewerManipulationPropertySet(_scrollViewer);
}
if (_scrollProperties == null)
{
return(false);
}
// Implicit operation: Find the Header object of the control if it uses ListViewBase
if (HeaderElement == null && listView != null)
{
HeaderElement = listView.Header as UIElement;
}
var headerElement = HeaderElement as FrameworkElement;
if (headerElement == null || headerElement.RenderSize.Height == 0)
{
return(false);
}
if (_headerVisual == null)
{
_headerVisual = ElementCompositionPreview.GetElementVisual(headerElement);
}
if (_headerVisual == null)
{
return(false);
}
headerElement.SizeChanged -= ScrollHeader_SizeChanged;
headerElement.SizeChanged += ScrollHeader_SizeChanged;
_scrollViewer.GotFocus -= ScrollViewer_GotFocus;
_scrollViewer.GotFocus += ScrollViewer_GotFocus;
var compositor = _scrollProperties.Compositor;
if (_animationProperties == null)
{
_animationProperties = compositor.CreatePropertySet();
_animationProperties.InsertScalar("OffsetY", 0.0f);
}
var propSetOffset = _animationProperties.GetReference().GetScalarProperty("OffsetY");
var scrollPropSet = _scrollProperties.GetSpecializedReference <ManipulationPropertySetReferenceNode>();
var expressionAnimation = ExpressionFunctions.Max(propSetOffset - scrollPropSet.Translation.Y, 0);
_headerVisual.StartAnimation("Offset.Y", expressionAnimation);
// Mod: clip items panel below header
var itemsPanel = listView.ItemsPanelRoot;
if (itemsPanel == null)
{
return(true);
}
if (_itemsPanelVisual == null)
{
_itemsPanelVisual = ElementCompositionPreview.GetElementVisual(itemsPanel);
_contentClip = compositor.CreateInsetClip();
_itemsPanelVisual.Clip = _contentClip;
}
var expressionClipAnimation = ExpressionFunctions.Max(-scrollPropSet.Translation.Y, 0);
_contentClip.TopInset = (float)System.Math.Max(-_scrollViewer.VerticalOffset, 0);
_contentClip.StartAnimation("TopInset", expressionClipAnimation);
return(true);
}
