fix(scrollviewer): [WASM] Make the SCP the "element which scrolls" (i…

…nstead of the SV)

src/Uno.UI/Generated/3.0.0.0/Windows.UI.Xaml.Controls/ScrollContentPresenter.cs

@@ -51,7 +51,7 @@ public  bool CanHorizontallyScroll
 		#endif
 		// Skipping already declared property ExtentHeight
 		// Skipping already declared property ExtentWidth
-		#if __ANDROID__ || __IOS__ || NET461 || __WASM__ || false || __NETSTD_REFERENCE__ || false
+		#if __ANDROID__ || __IOS__ || NET461 || false || false || __NETSTD_REFERENCE__ || false
 		[global::Uno.NotImplemented("__ANDROID__", "__IOS__", "NET461", "__WASM__", "__NETSTD_REFERENCE__", "__MACOS__")]
 		public  double HorizontalOffset
 		{
@@ -61,7 +61,7 @@ public  double HorizontalOffset
 			}
 		}
 		#endif
-		#if __ANDROID__ || __IOS__ || NET461 || __WASM__ || false || __NETSTD_REFERENCE__ || false
+		#if __ANDROID__ || __IOS__ || NET461 || false || false || __NETSTD_REFERENCE__ || false
 		[global::Uno.NotImplemented("__ANDROID__", "__IOS__", "NET461", "__WASM__", "__NETSTD_REFERENCE__", "__MACOS__")]
 		public  double VerticalOffset
 		{

src/Uno.UI/UI/Xaml/Controls/ScrollContentPresenter/ScrollContentPresenter.wasm.cs

@@ -37,6 +37,7 @@ internal Size ScrollBarSize
 
 		public ScrollContentPresenter()
 		{
+			RegisterAsScrollPort(this);
 		}
 
 		private void TryRegisterEvents(ScrollBarVisibility visibility)
@@ -143,6 +144,10 @@ public bool CanVerticallyScroll
 			set { }
 		}
 
+		public double HorizontalOffset { get; private set; }
+
+		public double VerticalOffset { get; private set; }
+
 		Size? IScrollContentPresenter.CustomContentExtent => null;
 
 		private protected override void OnLoaded()
@@ -248,11 +253,16 @@ private void OnScroll(object sender, EventArgs args)
 			// (the SV updates mode is always sync when isIntermediate is false).
 			var isIntermediate = false;
 
-			(TemplatedParent as ScrollViewer)?.OnScrollInternal(
-				GetNativeHorizontalOffset(),
-				GetNativeVerticalOffset(),
-				isIntermediate
-			);
+			var horizontalOffset = GetNativeHorizontalOffset();
+			var verticalOffset = GetNativeVerticalOffset();
+
+			HorizontalOffset = horizontalOffset;
+			VerticalOffset = verticalOffset;
+
+			(TemplatedParent as ScrollViewer)?.OnScrollInternal(horizontalOffset, verticalOffset, isIntermediate);
+
+			ScrollOffsets = new Point(horizontalOffset, verticalOffset);
+			InvalidateViewport();
 		}
 
 		private double GetNativeHorizontalOffset()

src/Uno.UI/UI/Xaml/Controls/ScrollViewer/ScrollViewer.MuxInternal.cs

@@ -3,6 +3,7 @@
 using System;
 using System.Collections.Generic;
 using System.Text;
+using Windows.Foundation;
 using Windows.UI.Xaml.Automation.Peers;
 using DirectUI;
 using Uno.Disposables;
@@ -17,10 +18,30 @@ partial class ScrollViewer
 
 		internal bool m_templatedParentHandlesMouseButton;
 
+		// Indicates whether ScrollViewer should ignore mouse wheel scroll events (not zoom).
+		internal bool ArePointerWheelEventsIgnored { get; set; } = false;
+		internal bool IsInManipulation => IsInDirectManipulation || m_isInConstantVelocityPan;
+
+		/// <summary>
+		/// Gets or set whether the <see cref="ScrollViewer"/> will allow scrolling outside of the ScrollViewer's Child bound.
+		/// </summary>		
+		internal bool ForceChangeToCurrentView { get; set; } = false;
 		internal bool IsInDirectManipulation { get; }
 		internal bool TemplatedParentHandlesScrolling { get; set; }
 		internal Func<AutomationPeer>? AutomationPeerFactoryIndex { get; set; }
 
+		internal bool BringIntoViewport(Rect bounds,
+			bool skipDuringTouchContact,
+			bool skipAnimationWhileRunning,
+			bool animate)
+		{
+#if __WASM__
+			return ChangeView(bounds.X, bounds.Y, null, true);
+#else
+			return ChangeView(bounds.X, bounds.Y, null, !animate);
+#endif
+		}
+
 		internal void SetDirectManipulationStateChangeHandler(IDirectManipulationStateChangeHandler? handler)
 		{
 			_directManipulationHandlerSubscription?.Dispose();

src/Uno.UI/UI/Xaml/Controls/ScrollViewer/ScrollViewer.cs

@@ -2,6 +2,10 @@
 #pragma warning disable CS0067
 #endif
 
+#if !UNO_HAS_MANAGED_SCROLL_PRESENTER && !__WASM__
+#define IS_SCROLL_PORT
+#endif
+
 #nullable enable
 
 using System;
@@ -119,7 +123,7 @@ public ScrollViewer()
 		{
 			DefaultStyleKey = typeof(ScrollViewer);
 
-#if !UNO_HAS_MANAGED_SCROLL_PRESENTER
+#if IS_SCROLL_PORT
 			// On Skia, the Scrolling is managed by the ScrollContentPresenter (as UWP), which is flagged as IsScrollPort.
 			// Note: We should still add support for the zoom factor ... which is not yet supported on Skia.
 			// Note 2: This as direct consequences in UIElement.GetTransform and VisualTreeHelper.SearchDownForTopMostElementAt
@@ -634,7 +638,6 @@ public double HorizontalOffset
 		/// </summary>
 		internal bool ComputedIsVerticalScrollEnabled { get; private set; } = false;
 
-
 		internal double MinHorizontalOffset => 0;
 
 		internal double MinVerticalOffset => 0;
@@ -1305,7 +1308,7 @@ private void Update(bool isIntermediate)
 
 			UpdatePartial(isIntermediate);
 
-#if !UNO_HAS_MANAGED_SCROLL_PRESENTER
+#if IS_SCROLL_PORT
 			// Effective viewport support
 			ScrollOffsets = new Point(_pendingHorizontalOffset, _pendingVerticalOffset);
 			InvalidateViewport();
@@ -1316,6 +1319,12 @@ private void Update(bool isIntermediate)
 
 		partial void UpdatePartial(bool isIntermediate);
 
+		public void ScrollToHorizontalOffset(double offset)
+			=> ChangeView(offset, null, null, false);
+
+		public void ScrollToVerticalOffset(double offset)
+			=> ChangeView(null, offset, null, false);
+
 		/// <summary>
 		/// Causes the ScrollViewer to load a new view into the viewport using the specified offsets and zoom factor, and optionally disables scrolling animation.
 		/// </summary>
@@ -1493,38 +1502,5 @@ private void HideScrollBarSeparator(object sender, PointerRoutedEventArgs e) //
 			}
 		}
 		#endregion
-
-		public void ScrollToHorizontalOffset(double offset)
-		{
-			_ = ChangeView(offset, null, null, false);
-		}
-
-		public void ScrollToVerticalOffset(double offset)
-		{
-			_ = ChangeView(null, offset, null, false);
-		}
-
-		// Indicates whether ScrollViewer should ignore mouse wheel scroll events (not zoom).
-		public bool ArePointerWheelEventsIgnored { get; set; } = false;
-
-		internal bool BringIntoViewport(Rect bounds,
-			bool skipDuringTouchContact,
-			bool skipAnimationWhileRunning,
-			bool animate)
-		{
-#if __WASM__
-			return ChangeView(bounds.X, bounds.Y, null, true);
-#else
-			return ChangeView(bounds.X, bounds.Y, null, !animate);
-#endif
-		}
-
-		internal bool IsInManipulation => IsInDirectManipulation || m_isInConstantVelocityPan;
-
-		/// <summary>
-		/// Gets or set whether the <see cref="ScrollViewer"/> will allow scrolling outside of the ScrollViewer's Child bound.
-		/// </summary>		
-		internal bool ForceChangeToCurrentView { get; set; } = false;
-
 	}
 }

src/Uno.UI/UI/Xaml/Media/VisualTreeHelper.cs

@@ -389,7 +389,7 @@ private static (UIElement? element, Branch? stale) SearchDownForTopMostElementAt
 				renderingBounds = parentToElement.Transform(renderingBounds);
 			}
 
-#if !UNO_HAS_MANAGED_SCROLL_PRESENTER
+#if !UNO_HAS_MANAGED_SCROLL_PRESENTER && !__WASM__
 			// On Skia, the Scrolling is managed by the ScrollContentPresenter (as UWP), which is flagged as IsScrollPort.
 			// Note: We should still add support for the zoom factor ... which is not yet supported on Skia.
 			if (element is ScrollViewer sv)
@@ -410,7 +410,7 @@ private static (UIElement? element, Branch? stale) SearchDownForTopMostElementAt
 			else
 #endif
 #if !__MACOS__ // On macOS the SCP is using RenderTransforms for scrolling which has already been included.
-			if (element.IsScrollPort)
+			if (element.IsScrollPort) // Managed SCP or custom scroller
 			{
 				posRelToElement.X += element.ScrollOffsets.X;
 				posRelToElement.Y += element.ScrollOffsets.Y;

src/Uno.UI/UI/Xaml/UIElement.cs

@@ -344,7 +344,7 @@ internal static Matrix3x2 GetTransform(UIElement from, UIElement to)
 					offsetY = layoutSlot.Y;
 				}
 
-#if !UNO_HAS_MANAGED_SCROLL_PRESENTER
+#if !UNO_HAS_MANAGED_SCROLL_PRESENTER && !__WASM__
 				// On Skia, the Scrolling is managed by the ScrollContentPresenter (as UWP), which is flagged as IsScrollPort.
 				// Note: We should still add support for the zoom factor ... which is not yet supported on Skia.
 				if (elt is ScrollViewer sv
@@ -372,7 +372,7 @@ internal static Matrix3x2 GetTransform(UIElement from, UIElement to)
 #if !__MACOS__ // On macOS the SCP is using RenderTransforms for scrolling which has already been included.
 				if (elt.IsScrollPort
 					// Don't adjust for scroll offsets if it's the scroll port itself calling TransformToVisual, only for ancestors
-					&& elt != from) // Custom scroller
+					&& elt != from) // Managed SCP or custom scroller
 				{
 					offsetX -= elt.ScrollOffsets.X;
 					offsetY -= elt.ScrollOffsets.Y;