chore: dont invalidate BorderVisual paths when the brush changes

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

@@ -29,6 +29,8 @@ internal class BorderVisual(Compositor compositor) : ShapeVisual(compositor)
 	private RectangleClip? _childClipCausedByCornerRadius;
 
 	// We do this instead of a direct SetProperty call so that SetProperty automatically gets an accurate propertyName
+	// we need the SetProperty calls to get notified on brush updates.
+	// (<Border|Background>Brush internals change -> <Border|Background>Shape is notified through FillBrush -> render invalidation)
 	private CompositionSpriteShape? BackgroundShape { set => SetProperty(ref _backgroundShape, value); }
 	private CompositionSpriteShape? BorderShape { set => SetProperty(ref _borderShape, value); }
 
@@ -55,13 +57,29 @@ public bool UseInnerBorderBoundsAsAreaForBackground
 	public CompositionBrush? BackgroundBrush
 	{
 		private get => _backgroundBrush;
-		set => SetProperty(ref _backgroundBrush, value);
+		set
+		{
+			if (_backgroundBrush is null)
+			{
+				// we skip the background path calculations while the background is null;
+				_backgroundPathValid = false;
+			}
+			SetProperty(ref _backgroundBrush, value);
+		}
 	}
 
 	public CompositionBrush? BorderBrush
 	{
 		private get => _borderBrush;
-		set => SetProperty(ref _borderBrush, value);
+		set
+		{
+			if (_borderBrush is null)
+			{
+				// we skip the border path calculations while the border is null;
+				_borderPathValid = false;
+			}
+			SetProperty(ref _borderBrush, value);
+		}
 	}
 
 	private protected override void OnPropertyChangedCore(string? propertyName, bool isSubPropertyChange)
@@ -78,11 +96,8 @@ private protected override void OnPropertyChangedCore(string? propertyName, bool
 			// BackgroundShape and BorderShape are NOT added to this.Shapes, which both makes it easier
 			// to reason about (no external tampering) and is also closer to what WinUI does.
 			case nameof(BorderBrush):
-				_borderPathValid = false; // to update _borderPath if previously skipped
 				if (BorderBrush is not null && _borderShape is null)
 				{
-					// we need this to get notified on brush updates
-					// (BorderBrush internals change -> BorderShape is notified through FillBrush -> render invalidation)
 					var borderShape = Compositor.CreateSpriteShape();
 					borderShape.Geometry = Compositor.CreatePathGeometry();
 #if DEBUG
@@ -97,11 +112,8 @@ private protected override void OnPropertyChangedCore(string? propertyName, bool
 				}
 				break;
 			case nameof(BackgroundBrush):
-				_backgroundPathValid = false; // to update _backgroundPath if previously skipped
 				if (BackgroundBrush is not null && _backgroundShape is null)
 				{
-					// we need this to get notified on brush updates.
-					// (BackgroundBrush internals change -> BackgroundShape is notified through FillBrush -> render invalidation)
 					var backgroundShape = Compositor.CreateSpriteShape();
 
 					backgroundShape.Geometry = Compositor.CreatePathGeometry();
@@ -170,7 +182,7 @@ private void UpdatePathsAndCornerClip()
 			fullCornerRadius.Outer.GetRadii(outerRadii);
 			fullCornerRadius.Inner.GetRadii(innerRadii);
 
-			if (_backgroundBrush is { } && !_backgroundPathValid)
+			if (_backgroundBrush is { } && !_backgroundPathValid) // no point calculating background state if the brush is null
 			{
 				_backgroundPathValid = true;
 				// We don't pass down <inner|outer>Area directly, since it contains the thickness offsets.
@@ -214,13 +226,16 @@ private void UpdatePathsAndCornerClip()
 				//    |                                           |
 				//    |                                           |
 				//    |-----------------300px---------------------|
-				UpdateBackgroundPath(_useInnerBorderBoundsAsAreaForBackground, innerArea.Size, outerArea.Size, outerRadii, innerRadii);
+
+				var backgroundPath = CreateBackgroundPath(_useInnerBorderBoundsAsAreaForBackground, innerArea.Size, outerArea.Size, outerRadii, innerRadii);
+				((CompositionPathGeometry)_backgroundShape!.Geometry!).Path = new CompositionPath(new SkiaGeometrySource2D(backgroundPath));
 				_backgroundShape!.Offset = _useInnerBorderBoundsAsAreaForBackground ? new Vector2((float)_borderThickness.Left, (float)_borderThickness.Top) : Vector2.Zero;
 			}
-			if (_borderBrush is { } && !_borderPathValid)
+			if (_borderBrush is { } && !_borderPathValid) // no point calculating border state if the brush is null
 			{
 				_borderPathValid = true;
-				UpdateBorderPath(innerArea, outerArea, outerRadii, innerRadii);
+				var borderPath = CreateBorderPath(innerArea, outerArea, outerRadii, innerRadii);
+				((CompositionPathGeometry)_borderShape!.Geometry!).Path = new CompositionPath(new SkiaGeometrySource2D(borderPath));
 			}
 		}
 
@@ -251,7 +266,7 @@ private void UpdatePathsAndCornerClip()
 		}
 	}
 
-	private unsafe void UpdateBackgroundPath(bool useInnerBorderBoundsAsAreaForBackground, SKSize innerArea, SKSize outerArea, SKPoint* outerRadii, SKPoint* innerRadii)
+	private static unsafe SKPath CreateBackgroundPath(bool useInnerBorderBoundsAsAreaForBackground, SKSize innerArea, SKSize outerArea, SKPoint* outerRadii, SKPoint* innerRadii)
 	{
 		var backgroundPath = new SKPath();
 		var roundRect = new SKRoundRect();
@@ -265,11 +280,10 @@ private unsafe void UpdateBackgroundPath(bool useInnerBorderBoundsAsAreaForBackg
 		backgroundPath.AddRoundRect(roundRect);
 		backgroundPath.Close();
 
-		// Unfortunately, this will cause an unnecessary render invalidation
-		((CompositionPathGeometry)_backgroundShape!.Geometry!).Path = new CompositionPath(new SkiaGeometrySource2D(backgroundPath));
+		return backgroundPath;
 	}
 
-	private unsafe void UpdateBorderPath(SKRect innerArea, SKRect outerArea, SKPoint* outerRadii, SKPoint* innerRadii)
+	private static unsafe SKPath CreateBorderPath(SKRect innerArea, SKRect outerArea, SKPoint* outerRadii, SKPoint* innerRadii)
 	{
 		var borderPath = new SKPath();
 
@@ -289,8 +303,7 @@ private unsafe void UpdateBorderPath(SKRect innerArea, SKRect outerArea, SKPoint
 			borderPath.Close();
 		}
 
-		// Unfortunately, this will cause an unnecessary render invalidation
-		((CompositionPathGeometry)_borderShape!.Geometry!).Path = new CompositionPath(new SkiaGeometrySource2D(borderPath));
+		return borderPath;
 	}
 
 	internal override bool HitTest(Point point)

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

@@ -11,7 +11,7 @@ internal static class UnoSkiaApi
 	unsafe internal static extern void sk_textblob_builder_alloc_run_pos(IntPtr builder, IntPtr font, int count, SKRect* bounds, UnoSKRunBufferInternal* runbuffer);
 
 	/// <summary>
-	/// We use this instead of the equivalent SKRoundRect.SetRectRadii because it take the array with a
+	/// We use this instead of the equivalent SKRoundRect.SetRectRadii because it takes an array with a
 	/// length of _exactly_ 4. If we rent the SKPoint array to reduce allocations, we're not guaranteed to
 	/// get the exact length we need.
 	/// </summary>