[Windows] Improve performance of ContentPanel.EnsureBorderPath (#22346

)

* Code style

* is null

* Cache children

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

@@ -1,5 +1,4 @@
-#nullable enable
-using System;
+using System;
 using System.Numerics;
 using Microsoft.Graphics.Canvas;
 using Microsoft.Maui.Graphics;
@@ -8,7 +7,6 @@
 using Microsoft.UI.Composition;
 using Microsoft.UI.Xaml;
 using Microsoft.UI.Xaml.Hosting;
-using Microsoft.UI.Xaml.Media;
 using Microsoft.UI.Xaml.Shapes;
 
 namespace Microsoft.Maui.Platform
@@ -50,38 +48,53 @@ internal FrameworkElement? Content
 		public ContentPanel()
 		{
 			_borderPath = new Path();
-			EnsureBorderPath();
+			EnsureBorderPath(containsCheck: false);
 
 			SizeChanged += ContentPanelSizeChanged;
 		}
 
-		void ContentPanelSizeChanged(object sender, UI.Xaml.SizeChangedEventArgs e)
+		void ContentPanelSizeChanged(object sender, SizeChangedEventArgs e)
 		{
 			if (_borderPath is null)
+			{
 				return;
+			}
 
 			var width = e.NewSize.Width;
 			var height = e.NewSize.Height;
 
 			if (width <= 0 || height <= 0)
+			{
 				return;
+			}
 
 			_borderPath.UpdatePath(_borderStroke?.Shape, width, height);
 			UpdateClip(_borderStroke?.Shape, width, height);
 		}
 
-		internal void EnsureBorderPath()
+		internal void EnsureBorderPath(bool containsCheck = true)
 		{
-			if (!Children.Contains(_borderPath))
+			if (containsCheck)
+			{
+				var children = Children;
+
+				if (!children.Contains(_borderPath))
+				{
+					children.Add(_borderPath);
+				}
+			}
+			else
 			{
 				Children.Add(_borderPath);
 			}
 		}
 
 		public void UpdateBackground(Paint? background)
 		{
-			if (_borderPath == null)
+			if (_borderPath is null)
+			{
 				return;
+			}
 
 			_borderPath.UpdateBackground(background);
 		}
@@ -95,61 +108,81 @@ public void UpdateBorderShape(IShape borderShape)
 		internal void UpdateBorderStroke(IBorderStroke borderStroke)
 		{
 			if (borderStroke is null)
+			{
 				return;
+			}
 
 			_borderStroke = borderStroke;
 
 			if (_borderStroke is null)
+			{
 				return;
+			}
 
 			UpdateBorder(_borderStroke.Shape);
 		}
 
 		void UpdateBorder(IShape? strokeShape)
 		{
 			if (strokeShape is null || _borderPath is null)
+			{
 				return;
+			}
 
 			_borderPath.UpdateBorderShape(strokeShape, ActualWidth, ActualHeight);
 
 			var width = ActualWidth;
 			var height = ActualHeight;
 
 			if (width <= 0 || height <= 0)
+			{
 				return;
+			}
 
 			UpdateClip(strokeShape, width, height);
 		}
 
 		void AddContent(FrameworkElement? content)
 		{
-			if (content == null)
+			if (content is null)
+			{
 				return;
+			}
 
-			if (!Children.Contains(_content))
-				Children.Add(_content);
+			var children = Children;
+
+			if (!children.Contains(_content))
+			{
+				children.Add(_content);
+			}
 		}
 
 		void UpdateClip(IShape? borderShape, double width, double height)
 		{
 			if (Content is null)
+			{
 				return;
+			}
 
 			if (height <= 0 && width <= 0)
+			{
 				return;
+			}
 
 			var clipGeometry = borderShape;
 
 			if (clipGeometry is null)
+			{
 				return;
+			}
 
 			var visual = ElementCompositionPreview.GetElementVisual(Content);
 			var compositor = visual.Compositor;
 
 			PathF? clipPath;
 			float strokeThickness = (float)(_borderPath?.StrokeThickness ?? 0);
 			// The path size should consider the space taken by the border (top and bottom, left and right)
-			var pathSize = new Graphics.Rect(0, 0, width - strokeThickness * 2, height - strokeThickness * 2);
+			var pathSize = new Rect(0, 0, width - strokeThickness * 2, height - strokeThickness * 2);
 
 			if (clipGeometry is IRoundRectangle roundedRectangle)
 			{