perf: reduce SKPaint and SKPath allocations

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

@@ -94,27 +94,37 @@ private SKPaint TryCreateAndClearStrokePaint(SKColorFilter? colorFilter)
 		private SKPaint TryCreateAndClearFillPaint(SKColorFilter? colorFilter)
 			=> TryCreateAndClearPaint(ref _fillPaint, false, colorFilter, CompositionConfiguration.UseBrushAntialiasing);
 
+		// TODO: profile the impact of this optimization and consider removing it
+		// It's hacky and can break if SkiaSharp exposes new properties that
+		// are then used and modified in CompositionBrush.UpdatePaint().
 		private static SKPaint TryCreateAndClearPaint(ref SKPaint? paint, bool isStroke, SKColorFilter? colorFilter, bool isHighQuality = false)
 		{
 			if (paint == null)
 			{
-				// Initialization
 				paint = new SKPaint();
-				paint.IsStroke = isStroke;
-				paint.IsAntialias = true;
-				paint.IsAutohinted = true;
-
-				if (isHighQuality)
-				{
-					paint.FilterQuality = SKFilterQuality.High;
-				}
 			}
 			else
 			{
+				// defaults
+				paint.IsAntialias = false;
+				paint.BlendMode = SKBlendMode.SrcOver;
+				paint.FakeBoldText = false;
+				paint.HintingLevel = SKPaintHinting.Normal;
+				paint.IsDither = false;
+				paint.IsEmbeddedBitmapText = false;
+				paint.IsLinearText = false;
+				paint.LcdRenderText = false;
+				paint.StrokeCap = SKStrokeCap.Butt;
+				paint.StrokeJoin = SKStrokeJoin.Miter;
+				paint.StrokeMiter = 4;
+				paint.StrokeWidth = 0;
+				paint.SubpixelText = false;
+				paint.TextAlign = SKTextAlign.Left;
+				paint.TextEncoding = SKTextEncoding.Utf8;
+				paint.TextScaleX = 1;
+				paint.TextSize = 12;
+
 				// 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();
@@ -126,9 +136,38 @@ private static SKPaint TryCreateAndClearPaint(ref SKPaint? paint, bool isStroke,
 					pathEffect.Dispose();
 					paint.PathEffect = null;
 				}
+
+				if (paint.ImageFilter is { } imageFilter)
+				{
+					imageFilter.Dispose();
+					paint.ImageFilter = null;
+				}
+
+				if (paint.MaskFilter is { } maskFilter)
+				{
+					maskFilter.Dispose();
+					paint.MaskFilter = null;
+				}
+
+				if (paint.Typeface is { } typeface)
+				{
+					typeface.Dispose();
+					paint.Typeface = null;
+				}
 			}
 
+			paint.IsStroke = isStroke;
+
+			// 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;
 		}

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);
+		}
 	}
 }