Extend dirty rect when UseLayoutRounding=false (#18511)

Co-authored-by: Benedikt Stebner <Gillibald@users.noreply.github.com>

src/Avalonia.Base/Layout/Layoutable.cs

@@ -948,5 +948,17 @@ namespace Avalonia.Layout
         {
             return new Size(Math.Max(size.Width, 0), Math.Max(size.Height, 0));
         }
+
+        internal override void SynchronizeCompositionProperties()
+        {
+            base.SynchronizeCompositionProperties();
+
+            if (CompositionVisual is { } visual)
+            {
+                // If the visual isn't using layout rounding, it's possible that antialiasing renders to pixels
+                // outside the current bounds. Extend the dirty rect by 1px in all directions in this case.
+                visual.ShouldExtendDirtyRect = !UseLayoutRounding;
+            }
+        }
     }
 }

src/Avalonia.Base/Rendering/Composition/Server/ServerCompositionVisual.cs

@@ -254,6 +254,12 @@ namespace Avalonia.Rendering.Composition.Server
         {
             if (rc == default)
                 return;
+
+            // If the visual isn't using layout rounding, it's possible that antialiasing renders to pixels
+            // outside the current bounds. Extend the dirty rect by 1px in all directions in this case.
+            if (ShouldExtendDirtyRect && RenderOptions.EdgeMode != EdgeMode.Aliased)
+                rc = rc.Inflate(new Thickness(1));
+
             Root?.AddDirtyRect(rc);
         }
 

src/Avalonia.Base/composition-schema.xml

@@ -34,6 +34,7 @@
         <Property Name="OpacityMaskBrush" ClientName="OpacityMaskBrushTransportField" Type="Avalonia.Media.IBrush?" Private="true"  />
         <Property Name="Effect" Type="Avalonia.Media.IImmutableEffect?" Internal="true" />
         <Property Name="RenderOptions" Type="Avalonia.Media.RenderOptions" />
+        <Property Name="ShouldExtendDirtyRect" Type="bool" Internal="true" />
     </Object>
     <Object Name="CompositionContainerVisual" Inherits="CompositionVisual"/>
     <Object Name="CompositionSolidColorVisual" Inherits="CompositionContainerVisual">