fix: Workaround jumping ScrollViewers on Skia

src/Uno.UI/Generated/3.0.0.0/Windows.UI.Xaml/UIElement.cs

@@ -94,8 +94,8 @@ namespace Windows.UI.Xaml
 			}
 		}
 		#endif
-		#if __ANDROID__ || __IOS__ || NET461 || __WASM__ || __SKIA__ || __NETSTD_REFERENCE__ || __MACOS__
-		[global::Uno.NotImplemented("__ANDROID__", "__IOS__", "NET461", "__WASM__", "__SKIA__", "__NETSTD_REFERENCE__", "__MACOS__")]
+		#if __ANDROID__ || __IOS__ || NET461 || __WASM__ || false || __NETSTD_REFERENCE__ || __MACOS__
+		[global::Uno.NotImplemented("__ANDROID__", "__IOS__", "NET461", "__WASM__", "__NETSTD_REFERENCE__", "__MACOS__")]
 		public  bool UseLayoutRounding
 		{
 			get
@@ -554,8 +554,8 @@ namespace Windows.UI.Xaml
 		// Skipping already declared property RightTappedEvent
 		// Skipping already declared property DragEnterEvent
 		// Skipping already declared property TappedEvent
-		#if __ANDROID__ || __IOS__ || NET461 || __WASM__ || __SKIA__ || __NETSTD_REFERENCE__ || __MACOS__
-		[global::Uno.NotImplemented("__ANDROID__", "__IOS__", "NET461", "__WASM__", "__SKIA__", "__NETSTD_REFERENCE__", "__MACOS__")]
+		#if __ANDROID__ || __IOS__ || NET461 || __WASM__ || false || __NETSTD_REFERENCE__ || __MACOS__
+		[global::Uno.NotImplemented("__ANDROID__", "__IOS__", "NET461", "__WASM__", "__NETSTD_REFERENCE__", "__MACOS__")]
 		public static global::Windows.UI.Xaml.DependencyProperty UseLayoutRoundingProperty { get; } = 
 		Windows.UI.Xaml.DependencyProperty.Register(
 			nameof(UseLayoutRounding), typeof(bool), 

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

@@ -21,6 +21,7 @@ using Windows.UI.Xaml.Input;
 using Uno;
 using Uno.Extensions;
 using Uno.Foundation.Logging;
+using Uno.UI.Extensions;
 
 
 #if __ANDROID__
@@ -49,6 +50,7 @@ using Microsoft.UI.Input;
 #else
 using Windows.Devices.Input;
 using Windows.UI.Input;
+using Windows.UI.Xaml.Media;
 #endif
 
 namespace Windows.UI.Xaml.Controls
@@ -775,23 +777,16 @@ namespace Windows.UI.Xaml.Controls
 				ExtentWidth = 0;
 			}
 
-			var scrollableHeight = Math.Max(ExtentHeight - ViewportHeight, 0);
-			// On Skia, the ExtentHeight can include a rounding error, which may cause
-			// unwanted ScrollBar to pop in and out of existence.
-			if (scrollableHeight < 0.1)
-			{
-				scrollableHeight = 0;
-			}
+			// For scrollable height and scrollable width we apply rounding
+			// to ensure there is no unwanted difference caused by double
+			// precision, which could then cause the scroll bars to appear
+			// for no reason.
+
+			var scrollableHeight = Math.Max(Math.Round(ExtentHeight - ViewportHeight, 4), 0);
 
 			ScrollableHeight = scrollableHeight;
 
-			var scrollableWidth = Math.Max(ExtentWidth - ViewportWidth, 0);
-			// On Skia, the ExtentWidth can include a rounding error, which may cause
-			// unwanted ScrollBar to pop in and out of existence.
-			if (scrollableWidth < 0.1)
-			{
-				scrollableWidth = 0;
-			}
+			var scrollableWidth = Math.Max(Math.Round(ExtentWidth - ViewportWidth, 4), 0);
 
 			ScrollableWidth = scrollableWidth;
 
@@ -941,6 +936,15 @@ namespace Windows.UI.Xaml.Controls
 
 			base.OnApplyTemplate();
 
+#if __SKIA__
+			// To work around non-uniformly applied layout rounding behavior, we need to force set layout
+			// rounding on the child Grid currently. #12082
+			if (this.FindFirstDescendant<Grid>() is { } grid)
+			{
+				grid.UseLayoutRounding = false;
+			}
+#endif
+
 			var scpTemplatePart = GetTemplateChild(Parts.WinUI3.Scroller) ?? GetTemplateChild(Parts.Uwp.ScrollContentPresenter);
 			_presenter = scpTemplatePart as _ScrollContentPresenter;
 

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

@@ -956,7 +956,7 @@ namespace Windows.UI.Xaml
 		internal bool GetUseLayoutRounding()
 		{
 #if __SKIA__
-			return true;
+			return UseLayoutRounding;
 #else
 			return false;
 #endif

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

@@ -41,6 +41,19 @@ namespace Windows.UI.Xaml
 			UpdateHitTest();
 		}
 
+		public bool UseLayoutRounding
+		{
+			get => (bool)this.GetValue(UseLayoutRoundingProperty);
+			set => this.SetValue(UseLayoutRoundingProperty, value);
+		}
+
+		public static DependencyProperty UseLayoutRoundingProperty { get; } =
+			DependencyProperty.Register(
+				nameof(UseLayoutRounding),
+				typeof(bool),
+				typeof(UIElement),
+				new FrameworkPropertyMetadata(true));
+
 		internal bool IsChildrenRenderOrderDirty { get; set; } = true;
 
 		partial void InitializeKeyboard();