perf: reduce SKPaint and SKPath allocations

src/Uno.UI.Composition/Composition/CompositionMaskBrush.skia.cs

@@ -14,7 +14,6 @@ public partial class CompositionMaskBrush : CompositionBrush, IOnlineBrush
 	{
 		private SKPaint? _sourcePaint;
 		private SKPaint? _maskPaint;
-		private SKPaint? _resultPaint;
 
 		bool IOnlineBrush.IsOnline
 		{
@@ -36,10 +35,11 @@ internal override void UpdatePaint(SKPaint paint, SKRect bounds)
 
 		void IOnlineBrush.Paint(in Visual.PaintingSession session, SKRect bounds)
 		{
-			_resultPaint ??= new SKPaint() { IsAntialias = true };
+			var resultPaint = SkiaHelper.GetTempSKPaint();
+			resultPaint.IsAntialias = true;
 
-			UpdatePaint(_resultPaint, bounds);
-			session.Canvas?.DrawRect(bounds, _resultPaint);
+			UpdatePaint(resultPaint, bounds);
+			session.Canvas?.DrawRect(bounds, resultPaint);
 		}
 
 		private protected override void DisposeInternal()
@@ -48,7 +48,6 @@ private protected override void DisposeInternal()
 
 			_sourcePaint?.Dispose();
 			_maskPaint?.Dispose();
-			_resultPaint?.Dispose();
 		}
 	}
 }

src/Uno.UI.Composition/Composition/CompositionSpriteShape.skia.cs

@@ -9,8 +9,6 @@ namespace Microsoft.UI.Composition
 {
 	public partial class CompositionSpriteShape : CompositionShape
 	{
-		private SKPaint? _strokePaint;
-		private SKPaint? _fillPaint;
 		private SKPath? _geometryWithTransformations;
 
 		internal override void Paint(in Visual.PaintingSession session)
@@ -19,7 +17,7 @@ internal override void Paint(in Visual.PaintingSession session)
 			{
 				if (FillBrush is { } fill)
 				{
-					var fillPaint = TryCreateAndClearFillPaint(session.Filters.OpacityColorFilter);
+					var fillPaint = GetTempFillPaint(session.Filters.OpacityColorFilter);
 
 					if (Compositor.TryGetEffectiveBackgroundColor(this, out var colorFromTransition))
 					{
@@ -52,8 +50,8 @@ internal override void Paint(in Visual.PaintingSession session)
 
 				if (StrokeBrush is { } stroke && StrokeThickness > 0)
 				{
-					var fillPaint = TryCreateAndClearFillPaint(session.Filters.OpacityColorFilter);
-					var strokePaint = TryCreateAndClearStrokePaint(session.Filters.OpacityColorFilter);
+					var fillPaint = GetTempFillPaint(session.Filters.OpacityColorFilter);
+					var strokePaint = GetTempStrokePaint(session.Filters.OpacityColorFilter);
 
 					// Set stroke thickness
 					strokePaint.StrokeWidth = StrokeThickness;
@@ -78,57 +76,41 @@ internal override void Paint(in Visual.PaintingSession session)
 					// On Windows, the stroke is simply 1px, it doesn't scale with the height.
 					// So, to get a correct stroke geometry, we must apply the transformations first.
 
+					var strokeFillPath = SkiaHelper.GetTempSKPath();
 					// Get the stroke geometry, after scaling has been applied.
-					var strokeGeometry = strokePaint.GetFillPath(geometryWithTransformations);
+					strokePaint.GetFillPath(geometryWithTransformations, strokeFillPath);
 
-					stroke.UpdatePaint(fillPaint, strokeGeometry.Bounds);
+					stroke.UpdatePaint(fillPaint, strokeFillPath.Bounds);
 
-					session.Canvas.DrawPath(strokeGeometry, fillPaint);
+					session.Canvas.DrawPath(strokeFillPath, fillPaint);
 				}
 			}
 		}
 
-		private SKPaint TryCreateAndClearStrokePaint(SKColorFilter? colorFilter)
-			=> TryCreateAndClearPaint(ref _strokePaint, true, colorFilter, CompositionConfiguration.UseBrushAntialiasing);
+		private SKPaint GetTempStrokePaint(SKColorFilter? colorFilter)
+			=> GetTempPaint(true, colorFilter, CompositionConfiguration.UseBrushAntialiasing);
 
-		private SKPaint TryCreateAndClearFillPaint(SKColorFilter? colorFilter)
-			=> TryCreateAndClearPaint(ref _fillPaint, false, colorFilter, CompositionConfiguration.UseBrushAntialiasing);
+		private SKPaint GetTempFillPaint(SKColorFilter? colorFilter)
+			=> GetTempPaint(false, colorFilter, CompositionConfiguration.UseBrushAntialiasing);
 
-		private static SKPaint TryCreateAndClearPaint(ref SKPaint? paint, bool isStroke, SKColorFilter? colorFilter, bool isHighQuality = false)
+		private static SKPaint GetTempPaint(bool isStroke, SKColorFilter? colorFilter, bool isHighQuality = false)
 		{
-			if (paint == null)
-			{
-				// Initialization
-				paint = new SKPaint();
-				paint.IsStroke = isStroke;
-				paint.IsAntialias = true;
-				paint.IsAutohinted = true;
+			var paint = isStroke ? SkiaHelper.GetTempSKPaint() : SkiaHelper.GetAnotherTempSKPaint();
+			paint.IsAntialias = true;
+			paint.ColorFilter = colorFilter;
 
-				if (isHighQuality)
-				{
-					paint.FilterQuality = SKFilterQuality.High;
-				}
-			}
-			else
-			{
-				// Cleanup
-				// - Brushes can change, we cant leave color and shader garbage
-				//	 from last rendering around for the next pass.
-				paint.Color = SKColors.White;   // Transparent color wouldn't draw anything
-				if (paint.Shader is { } shader)
-				{
-					shader.Dispose();
-					paint.Shader = null;
-				}
+			paint.IsStroke = isStroke;
 
-				if (paint.PathEffect is { } pathEffect)
-				{
-					pathEffect.Dispose();
-					paint.PathEffect = null;
-				}
-			}
+			// uno-specific defaults
+			paint.Color = SKColors.White;   // Transparent color wouldn't draw anything
+			paint.IsAutohinted = true;
+			// paint.IsAntialias = true; // IMPORTANT: don't set this to true by default. It breaks canvas clipping on Linux for some reason.
 
 			paint.ColorFilter = colorFilter;
+			if (isHighQuality)
+			{
+				paint.FilterQuality = SKFilterQuality.High;
+			}
 
 			return paint;
 		}
@@ -177,10 +159,12 @@ internal override bool HitTest(Point point)
 
 				if (StrokeBrush is { } stroke && StrokeThickness > 0)
 				{
-					var strokePaint = TryCreateAndClearStrokePaint(null);
+					var strokePaint = GetTempStrokePaint(null);
 					strokePaint.StrokeWidth = StrokeThickness;
-					var strokeGeometry = strokePaint.GetFillPath(geometryWithTransformations);
-					if (strokeGeometry.Contains((float)point.X, (float)point.Y))
+
+					var hitTestStrokeFillPath = SkiaHelper.GetTempSKPath();
+					strokePaint.GetFillPath(geometryWithTransformations, hitTestStrokeFillPath);
+					if (hitTestStrokeFillPath.Contains((float)point.X, (float)point.Y))
 					{
 						return true;
 					}

src/Uno.UI.Composition/Composition/ShapeVisual.skia.cs

@@ -1,5 +1,6 @@
 #nullable enable
 
+using System;
 using System.Numerics;
 using Windows.Foundation;
 using SkiaSharp;
@@ -9,12 +10,16 @@ namespace Microsoft.UI.Composition;
 
 public partial class ShapeVisual
 {
+	[ThreadStatic] // safety
+	private static SKPath? _prePaintingClipPath;
+
 	private protected override void ApplyPrePaintingClipping(in SKCanvas canvas)
 	{
 		base.ApplyPrePaintingClipping(in canvas);
-		if (GetViewBoxPathInElementCoordinateSpace() is { } path)
+		_prePaintingClipPath ??= new SKPath();
+		if (GetViewBoxPathInElementCoordinateSpace(_prePaintingClipPath))
 		{
-			canvas.ClipPath(path, antialias: true);
+			canvas.ClipPath(_prePaintingClipPath, antialias: true);
 		}
 	}
 
@@ -32,28 +37,28 @@ internal override void Paint(in PaintingSession session)
 		base.Paint(in session);
 	}
 
-	internal SKPath? GetViewBoxPathInElementCoordinateSpace()
+	/// <returns>The same <see cref="dst"/> object.</returns>
+	internal bool GetViewBoxPathInElementCoordinateSpace(SKPath dst)
 	{
 		if (ViewBox is not { } viewBox)
 		{
-			return null;
+			return false;
 		}
 
-		var shape = new SKPath();
+		dst.Rewind();
 		var clipRect = new SKRect(viewBox.Offset.X, viewBox.Offset.Y, viewBox.Offset.X + viewBox.Size.X, viewBox.Offset.Y + viewBox.Size.Y);
-		shape.AddRect(clipRect);
+		dst.AddRect(clipRect);
 		if (viewBox.IsAncestorClip)
 		{
 			Matrix4x4.Invert(TotalMatrix, out var totalMatrixInverted);
 			var childToParentTransform = Parent!.TotalMatrix * totalMatrixInverted;
 			if (!childToParentTransform.IsIdentity)
 			{
-
-				shape.Transform(childToParentTransform.ToSKMatrix());
+				dst.Transform(childToParentTransform.ToSKMatrix());
 			}
 		}
 
-		return shape;
+		return true;
 	}
 
 	/// <remarks>This does NOT take the clipping into account.</remarks>

src/Uno.UI.Composition/Composition/SkiaHelper.skia.cs

@@ -0,0 +1,43 @@
+#nullable enable
+
+using SkiaSharp;
+using System;
+using System.Collections.Generic;
+using System.Numerics;
+using System.Text;
+using Windows.Foundation;
+using Windows.UI;
+
+namespace Microsoft.UI.Composition
+{
+	public static class SkiaHelper
+	{
+		[ThreadStatic] private static readonly SKPath _tempPath = new SKPath();
+		[ThreadStatic] private static readonly SKPaint _tempPaint = new SKPaint();
+		[ThreadStatic] private static readonly SKPaint _tempPaint2 = new SKPaint();
+
+		public static SKPath GetTempSKPath()
+		{
+			// Note the difference between Rewind and Reset
+			// https://api.skia.org/classSkPath.html#a8dc858ee4c95a59b3dd4bdd3f7b85fdc : "Use rewind() instead of reset() if SkPath storage will be reused and performance is critical."
+			_tempPath.Rewind();
+			return _tempPath;
+		}
+
+		public static SKPaint GetTempSKPaint()
+		{
+			// https://api.skia.org/classSkPaint.html#a6c7118c97a0e8819d75aa757afbc4c49
+			// "This is equivalent to replacing SkPaint with the result of SkPaint()."
+			_tempPaint.Reset();
+			return _tempPaint;
+		}
+
+		public static SKPaint GetAnotherTempSKPaint()
+		{
+			// https://api.skia.org/classSkPaint.html#a6c7118c97a0e8819d75aa757afbc4c49
+			// "This is equivalent to replacing SkPaint with the result of SkPaint()."
+			_tempPaint2.Reset();
+			return _tempPaint2;
+		}
+	}
+}

src/Uno.UI.RuntimeTests/Tests/Windows_UI_Xaml_Shapes/Given_Path.cs

@@ -1,17 +1,22 @@
 using System;
-using Windows.Foundation;
+using System.Threading.Tasks;
+using Microsoft.UI.Xaml;
+using Microsoft.UI.Xaml.Controls;
 using Microsoft.UI.Xaml.Markup;
 using Microsoft.UI.Xaml.Media;
 using Microsoft.UI.Xaml.Shapes;
+using MUXControlsTestApp.Utilities;
 using SamplesApp.UITests;
+using Uno.UI.RuntimeTests.Helpers;
+using Size = Windows.Foundation.Size;
 
 namespace Uno.UI.RuntimeTests.Tests.Windows_UI_Xaml_Shapes
 {
 	[TestClass]
+	[RunsOnUIThread]
 	public class Given_Path
 	{
 		[TestMethod]
-		[RunsOnUIThread]
 		[UnoWorkItem("https://github.com/unoplatform/uno/issues/6846")]
 		public void Should_not_throw_if_Path_Data_is_set_to_null()
 		{
@@ -23,7 +28,6 @@ public void Should_not_throw_if_Path_Data_is_set_to_null()
 		}
 
 		[TestMethod]
-		[RunsOnUIThread]
 		public void Should_Not_Include_Control_Points_Bounds()
 		{
 #if WINAPPSDK
@@ -41,5 +45,29 @@ public void Should_Not_Include_Control_Points_Bounds()
 			Assert.IsTrue(Math.Abs(50 - SUT.DesiredSize.Height) <= 1, $"Actual size: {SUT.DesiredSize}");
 #endif
 		}
+
+		// This tests a workaround for a Linux-specific skia bug.
+		// This doesn't actually repro for some reason, so it's here for documentation purposes.
+		[TestMethod]
+		[UnoWorkItem("https://github.com/unoplatform/uno/issues/18473")]
+		public async Task When_Path_Clipped_Inside_ScrollViewer()
+		{
+			var root = (FrameworkElement)XamlReader.Load(
+				"""
+				<StackPanel xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+					<Border Height="100" HorizontalAlignment="Stretch" Background="Blue" />
+					<ScrollViewer Height="30">
+						<Path Fill="Red" Data="m 0,0 c -0.639,0 -1.276,0.243 -1.765,0.729 -0.977,0.974 -0.98,2.557 -0.006,3.535 L 16.925,23.032 -1.768,41.725 c -0.976,0.976 -0.976,2.559 0,3.535 0.977,0.976 2.559,0.976 3.536,0 L 22.225,24.803 c 0.975,-0.975 0.976,-2.555 0.004,-3.532 L 1.771,0.736 C 1.283,0.245 0.642,0 0,0" />
+					</ScrollViewer>
+				</StackPanel>
+				""");
+			await UITestHelper.Load(root);
+
+			root.FindVisualChildByType<ScrollViewer>().ScrollToVerticalOffset(9999);
+			await UITestHelper.WaitForIdle();
+
+			var screenshot = await UITestHelper.ScreenShot(root);
+			ImageAssert.DoesNotHaveColorInRectangle(screenshot, new System.Drawing.Rectangle(0, 0, screenshot.Width, screenshot.Height * 60 / 100), Microsoft.UI.Colors.Red);
+		}
 	}
 }

src/Uno.UI/UI/Xaml/Controls/TextBlock/TextBlock.skia.cs

@@ -16,6 +16,7 @@
 using Uno.UI.Xaml.Core;
 using Uno.UI.Xaml.Media;
 using Uno.UI.Xaml.Core.Scaling;
+using SkiaExtensions = Microsoft.UI.Composition.SkiaExtensions;
 
 #nullable enable
 
@@ -188,11 +189,11 @@ partial void SetupInlines()
 			{
 				var canvas = t.canvas;
 				var rect = t.rect;
-				canvas.DrawRect(new SKRect((float)rect.Left, (float)rect.Top, (float)rect.Right, (float)rect.Bottom), new SKPaint
-				{
-					Color = SelectionHighlightColor.Color.ToSKColor(),
-					Style = SKPaintStyle.Fill
-				});
+
+				var paint = SkiaHelper.GetTempSKPaint();
+				paint.Color = SelectionHighlightColor.Color.ToSKColor();
+				paint.Style = SKPaintStyle.Fill;
+				canvas.DrawRect(new SKRect((float)rect.Left, (float)rect.Top, (float)rect.Right, (float)rect.Bottom), paint);
 			};
 
 			_inlines.RenderSelection = IsTextSelectionEnabled;

src/Uno.UI/UI/Xaml/Controls/TextBox/TextBox.skia.cs

@@ -239,7 +239,7 @@ private void UpdateTextBoxView()
 							var caretRect = args.rect;
 							var compositor = _visual.Compositor;
 							var brush = DefaultBrushes.TextForegroundBrush.GetOrCreateCompositionBrush(compositor);
-							var caretPaint = new SKPaint(); // we create a new caret everytime to dodge the complications that occur when trying to "reset" an SKPaint.
+							var caretPaint = SkiaHelper.GetTempSKPaint();
 							brush.UpdatePaint(caretPaint, caretRect.ToSKRect());
 							args.canvas.DrawRect(
 								new SKRect((float)caretRect.Left, (float)caretRect.Top, (float)caretRect.Right,

src/Uno.UI/UI/Xaml/Documents/Inline.skia.cs

@@ -10,22 +10,6 @@ namespace Microsoft.UI.Xaml.Documents
 	partial class Inline
 	{
 		private FontDetails? _fontInfo;
-		private SKPaint? _paint;
-
-		internal SKPaint Paint
-		{
-			get
-			{
-				var paint = _paint ??= new SKPaint()
-				{
-					TextEncoding = SKTextEncoding.Utf16,
-					IsStroke = false,
-					IsAntialias = true,
-				};
-
-				return paint;
-			}
-		}
 
 		internal FontDetails FontInfo
 		{