[Windows] Fix Border content position and clipping

src/Controls/samples/Controls.Sample/Pages/Core/BordersPage.xaml

@@ -22,7 +22,7 @@
         </Grid.RowDefinitions>
 
         <Border x:Name="BorderView" Margin="5">
-            <Label Text="Just a Label" FontSize="20"/>
+            <Label x:Name="BorderContent" Text="Just a Label" FontSize="20"/>
         </Border>
 
         <ScrollView
@@ -61,6 +61,20 @@
                     Text="#0083B0"
                     Placeholder="Background End Color Hex"
                     TextChanged="OnBackgroundChanged"/>
+                <Label
+                    Text="Content Background"
+                    Style="{StaticResource Headline}"/>
+                <StackLayout
+                    Orientation="Horizontal">
+                    <CheckBox 
+                        x:Name="ContentBackgroundCheckBox"
+                        WidthRequest="48"
+                        VerticalOptions="Center"
+                        CheckedChanged="OnContentBackgroundCheckBoxChanged"/>
+                    <Label 
+                        Text="Show Content Background"
+                        VerticalOptions="Center"/>
+                </StackLayout>
                 <Label
                     Text="Border"
                     Style="{StaticResource Headline}"/>

src/Controls/samples/Controls.Sample/Pages/Core/BordersPage.xaml.cs

@@ -17,6 +17,7 @@ public BordersPage()
 			BorderLineCapPicker.SelectedIndex = 0;
 
 			UpdateBackground();
+			UpdateContentBackground();
 			UpdateBorder();
 			UpdateCornerRadius();
 		}
@@ -66,6 +67,11 @@ void OnCornerRadiusChanged(object sender, ValueChangedEventArgs e)
 			UpdateCornerRadius();
 		}
 
+		void OnContentBackgroundCheckBoxChanged(object sender, CheckedChangedEventArgs e)
+		{
+			UpdateContentBackground();
+		}
+
 		void UpdateBorderShape()
 		{
 			CornerRadiusLayout.IsVisible = BorderShapePicker.SelectedIndex == 1;
@@ -93,6 +99,11 @@ void UpdateBackground()
 			};
 		}
 
+		void UpdateContentBackground()
+		{
+			BorderContent.BackgroundColor = ContentBackgroundCheckBox.IsChecked ? Color.FromArgb("#99FF0000") : Colors.Transparent;
+		}
+
 		void UpdateBorder()
 		{
 			var startColor = GetColorFromString(BorderStartColor.Text);

src/Controls/samples/Controls.Sample/ViewModels/ControlsViewModel.cs

@@ -11,6 +11,9 @@ protected override IEnumerable<SectionModel> CreateItems() => new[]
 		{
 			new SectionModel(typeof(ActivityIndicatorPage), "ActivityIndicator",
 				"Displays an animation to show that the application is engaged in a lengthy activity."),
+
+			new SectionModel(typeof(BordersPage), "Border",
+				"Draws a border around a View."),
 
 			new SectionModel(typeof(BoxViewPage), "BoxView",
 				"BoxView renders a simple rectangle of a specified width, height, and color. You can use BoxView for decoration, rudimentary graphics, and for interaction with the user through touch."),

src/Controls/samples/Controls.Sample/ViewModels/CoreViewModel.cs

@@ -18,9 +18,6 @@ protected override IEnumerable<SectionModel> CreateItems() => new[]
 			new SectionModel(typeof(AppThemeBindingPage), "AppThemeBindings",
 				"Devices typically include light and dark themes, which each refer to a broad set of appearance preferences that can be set at the operating system level. Applications should respect these system themes, and respond immediately when the system theme changes."),
 
-			new SectionModel(typeof(BordersPage), "Borders",
-				"Draws a border around a View, Layout, or Control."),
-
 			new SectionModel(typeof(BrushesPage), "Brushes",
 				"A brush enables you to paint an area, such as the background of a control, using different approaches."),
 

src/Controls/samples/Controls.Sample/ViewModels/MainViewModel.cs

@@ -60,9 +60,6 @@ protected override IEnumerable<SectionModel> CreateItems() => new[]
 
 			new SectionModel(typeof(OthersPage), "Others Concepts",
 				"Other options like Graphics."),
-
-			new SectionModel(typeof(HitTestingPage), "Hit Testing",
-				"Demonstrates VisualTreeElementExtensions hit testing methods"),
 		};
 	}
 }

src/Controls/samples/Controls.Sample/ViewModels/OthersViewModel.cs

@@ -11,14 +11,21 @@ protected override IEnumerable<SectionModel> CreateItems() => new[]
 		{
 			new SectionModel(typeof(GraphicsViewPage), "GraphicsView",
 				"Allow to draw directly in a Canvas. You can combine a canvas and native Views on the same page."),
+
 			new SectionModel(typeof(LargeTitlesPageiOS), "Large Titles - iOS",
 				"This iOS platform-specific is used to display the page title as a large title on the navigation bar of a NavigationPage, for devices that use iOS 11 or greater."),
+
 			new SectionModel(typeof(StyleSheetsPage), "StyleSheets",
 				"Demonstrates the usage of CSS in XAML."),
+
 			new SectionModel(typeof(TwoPaneViewPage), "Foldable",
 				"Demonstrates the usage of TwoPaneView and hinge sensor."),
+
 			new SectionModel(typeof(RenderViewPage), "Render Views",
-				"Demonstrates rendering views as images.")
+				"Demonstrates rendering views as images."),
+
+			new SectionModel(typeof(HitTestingPage), "Hit Testing",
+				"Demonstrates VisualTreeElementExtensions hit testing methods"),
 		};
 	}
 }

src/Controls/src/Core/Border.cs

@@ -1,6 +1,7 @@
 #nullable enable
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
+using System.Runtime.CompilerServices;
 using Microsoft.Maui.Controls.Shapes;
 using Microsoft.Maui.Graphics;
 using Microsoft.Maui.Layouts;
@@ -191,5 +192,15 @@ public Thickness PaddingDefaultValueCreator()
 		{
 			return Thickness.Zero;
 		}
+
+		protected override void OnPropertyChanged([CallerMemberName] string? propertyName = null)
+		{
+			base.OnPropertyChanged(propertyName);
+
+			if (propertyName == HeightProperty.PropertyName ||
+				propertyName == WidthProperty.PropertyName ||
+				propertyName == StrokeShapeProperty.PropertyName)
+				Handler?.UpdateValue(nameof(IBorderStroke.Shape));
+		}
 	}
 }

src/Controls/src/Core/HandlerImpl/RoundRectangle.Impl.cs

@@ -1,9 +1,18 @@
-using Microsoft.Maui.Graphics;
+using System.Runtime.CompilerServices;
+using Microsoft.Maui.Graphics;
 
 namespace Microsoft.Maui.Controls.Shapes
 {
 	public partial class RoundRectangle : IShape
 	{
+		protected override void OnPropertyChanged([CallerMemberName] string propertyName = null)
+		{
+			base.OnPropertyChanged(propertyName);
+
+			if (propertyName == CornerRadiusProperty.PropertyName)
+				Handler?.UpdateValue(nameof(IShapeView.Shape));
+		}
+
 		public override PathF GetPath()
 		{
 			var path = new PathF();

src/Core/src/Handlers/Border/BorderHandler.Windows.cs

@@ -3,46 +3,46 @@
 namespace Microsoft.Maui.Handlers
 {
 	public partial class BorderHandler : ViewHandler<IBorderView, ContentPanel>
-    {
-        public override void SetVirtualView(IView view)
-        {
-            base.SetVirtualView(view);
+	{
+		public override void SetVirtualView(IView view)
+		{
+			base.SetVirtualView(view);
 
-            _ = PlatformView ?? throw new InvalidOperationException($"{nameof(PlatformView)} should have been set by base class.");
-            _ = VirtualView ?? throw new InvalidOperationException($"{nameof(VirtualView)} should have been set by base class.");
+			_ = PlatformView ?? throw new InvalidOperationException($"{nameof(PlatformView)} should have been set by base class.");
+			_ = VirtualView ?? throw new InvalidOperationException($"{nameof(VirtualView)} should have been set by base class.");
 
-            PlatformView.CrossPlatformMeasure = VirtualView.CrossPlatformMeasure;
-            PlatformView.CrossPlatformArrange = VirtualView.CrossPlatformArrange;
-        }
+			PlatformView.CrossPlatformMeasure = VirtualView.CrossPlatformMeasure;
+			PlatformView.CrossPlatformArrange = VirtualView.CrossPlatformArrange;
+		}
 
-        static void UpdateContent(IBorderHandler handler)
-        {
-            _ = handler.PlatformView ?? throw new InvalidOperationException($"{nameof(PlatformView)} should have been set by base class.");
-            _ = handler.VirtualView ?? throw new InvalidOperationException($"{nameof(VirtualView)} should have been set by base class.");
-            _ = handler.MauiContext ?? throw new InvalidOperationException($"{nameof(MauiContext)} should have been set by base class.");
+		static void UpdateContent(IBorderHandler handler)
+		{
+			_ = handler.PlatformView ?? throw new InvalidOperationException($"{nameof(PlatformView)} should have been set by base class.");
+			_ = handler.VirtualView ?? throw new InvalidOperationException($"{nameof(VirtualView)} should have been set by base class.");
+			_ = handler.MauiContext ?? throw new InvalidOperationException($"{nameof(MauiContext)} should have been set by base class.");
 
 			handler.PlatformView.Children.Clear();
 			handler.PlatformView.EnsureBorderPath();
 
-            if (handler.VirtualView.PresentedContent is IView view)
-				handler.PlatformView.Children.Add(view.ToPlatform(handler.MauiContext));
-        }
+			if (handler.VirtualView.PresentedContent is IView view)
+				handler.PlatformView.Content = view.ToPlatform(handler.MauiContext);
+		}
 
-        protected override ContentPanel CreatePlatformView()
-        {
-            if (VirtualView == null)
-            {
-                throw new InvalidOperationException($"{nameof(VirtualView)} must be set to create a LayoutView");
-            }
+		protected override ContentPanel CreatePlatformView()
+		{
+			if (VirtualView == null)
+			{
+				throw new InvalidOperationException($"{nameof(VirtualView)} must be set to create a LayoutView");
+			}
 
-            var view = new ContentPanel
+			var view = new ContentPanel
 			{
-                CrossPlatformMeasure = VirtualView.CrossPlatformMeasure,
-                CrossPlatformArrange = VirtualView.CrossPlatformArrange
-            };
+				CrossPlatformMeasure = VirtualView.CrossPlatformMeasure,
+				CrossPlatformArrange = VirtualView.CrossPlatformArrange
+			};
 
-            return view;
-        }
+			return view;
+		}
 
 		public static void MapContent(IBorderHandler handler, IBorderView border)
 		{

src/Core/src/Platform/Windows/ContentPanel.cs

@@ -1,7 +1,13 @@
 #nullable enable
 using System;
+using Microsoft.Graphics.Canvas;
 using Microsoft.Maui.Graphics;
+using Microsoft.Maui.Graphics.Win2D;
+using Microsoft.UI.Composition;
+using Microsoft.UI.Xaml;
 using Microsoft.UI.Xaml.Controls;
+using Microsoft.UI.Xaml.Hosting;
+using Microsoft.UI.Xaml.Media;
 using Microsoft.UI.Xaml.Shapes;
 
 namespace Microsoft.Maui.Platform
@@ -10,8 +16,20 @@ public class ContentPanel : Panel
 	{
 		readonly Path? _borderPath;
 		IShape? _borderShape;
+		FrameworkElement? _content;
 
 		internal Path? BorderPath => _borderPath;
+
+		internal FrameworkElement? Content
+		{
+			get => _content;
+			set
+			{
+				_content = value;
+				AddContent(_content);
+			}
+		}
+
 		internal Func<double, double, Size>? CrossPlatformMeasure { get; set; }
 		internal Func<Graphics.Rect, Size>? CrossPlatformArrange { get; set; }
 
@@ -52,12 +70,14 @@ public ContentPanel()
 			SizeChanged += ContentPanelSizeChanged;
 		}
 
-		private void ContentPanelSizeChanged(object sender, UI.Xaml.SizeChangedEventArgs e)
+		void ContentPanelSizeChanged(object sender, UI.Xaml.SizeChangedEventArgs e)
 		{
 			if (_borderPath == null)
 				return;
 
 			_borderPath.UpdatePath(_borderShape, ActualWidth, ActualHeight);
+			UpdateContent();
+			UpdateClip(_borderShape);
 		}
 
 		internal void EnsureBorderPath()
@@ -84,6 +104,58 @@ public void UpdateBorderShape(IShape borderShape)
 				return;
 
 			_borderPath.UpdateBorderShape(_borderShape, ActualWidth, ActualHeight);
+			UpdateContent();
+			UpdateClip(_borderShape);
+		}
+
+		void AddContent(FrameworkElement? content)
+		{
+			if (content == null)
+				return;
+
+			if (!Children.Contains(_content))
+				Children.Add(_content);
+		}
+
+		void UpdateContent()
+		{
+			if (Content == null || _borderPath == null)
+				return;
+
+			var strokeThickness = _borderPath.StrokeThickness;
+
+			Content.RenderTransform = new TranslateTransform() { X = -strokeThickness, Y = -strokeThickness };
+		}
+
+		void UpdateClip(IShape? borderShape)
+		{
+			if (Content == null)
+				return;
+
+			var clipGeometry = borderShape;
+
+			if (clipGeometry == null)
+				return;
+
+			double width = Content.ActualWidth;
+			double height = Content.ActualHeight;
+
+			if (height <= 0 && width <= 0)
+				return;
+
+			var visual = ElementCompositionPreview.GetElementVisual(Content);
+			var compositor = visual.Compositor;
+
+			var pathSize = new Graphics.Rect(0, 0, width, height);
+			var clipPath = clipGeometry.PathForBounds(pathSize);
+			var device = CanvasDevice.GetSharedDevice();
+			var geometry = clipPath.AsPath(device);
+
+			var path = new CompositionPath(geometry);
+			var pathGeometry = compositor.CreatePathGeometry(path);
+			var geometricClip = compositor.CreateGeometricClip(pathGeometry);
+
+			visual.Clip = geometricClip;
 		}
 	}
 }