Don't use AvaloniaObject in IPlatformRenderInterface

src/Avalonia.Base/CombinedGeometry.cs

@@ -152,19 +152,15 @@ namespace Avalonia.Media
             var g1 = Geometry1;
             var g2 = Geometry2;
 
-            if (g1 is object && g2 is object)
+            if (g1?.PlatformImpl != null && g2?.PlatformImpl != null)
             {
                 var factory = AvaloniaLocator.Current.GetRequiredService<IPlatformRenderInterface>();
-                return factory.CreateCombinedGeometry(GeometryCombineMode, g1, g2);
+                return factory.CreateCombinedGeometry(GeometryCombineMode, g1.PlatformImpl, g2.PlatformImpl);
             }
-            else if (GeometryCombineMode == GeometryCombineMode.Intersect)
-                return null;
-            else if (g1 is object)
-                return g1.PlatformImpl;
-            else if (g2 is object)
-                return g2.PlatformImpl;
-            else
+
+            if (GeometryCombineMode == GeometryCombineMode.Intersect)
                 return null;
+            return g1?.PlatformImpl ?? g2?.PlatformImpl;
         }
     }
 }

src/Avalonia.Base/Media/GeometryGroup.cs

@@ -78,7 +78,10 @@ namespace Avalonia.Media
             {
                 var factory = AvaloniaLocator.Current.GetRequiredService<IPlatformRenderInterface>();
 
-                return factory.CreateGeometryGroup(FillRule, _children);
+                var children = new IGeometryImpl?[_children.Count];
+                for (var c = 0; c < _children.Count; c++)
+                    children[c] = _children[c].PlatformImpl;
+                return factory.CreateGeometryGroup(FillRule, children!);
             }
 
             return null;

src/Avalonia.Base/Platform/IPlatformRenderInterface.cs

@@ -48,7 +48,7 @@ namespace Avalonia.Platform
         /// <param name="fillRule">The fill rule.</param>
         /// <param name="children">The geometries to group.</param>
         /// <returns>A combined geometry.</returns>
-        IGeometryImpl CreateGeometryGroup(FillRule fillRule, IReadOnlyList<Geometry> children);
+        IGeometryImpl CreateGeometryGroup(FillRule fillRule, IReadOnlyList<IGeometryImpl> children);
 
         /// <summary>
         /// Creates a geometry group implementation.
@@ -57,7 +57,7 @@ namespace Avalonia.Platform
         /// <param name="g1">The first geometry.</param>
         /// <param name="g2">The second geometry.</param>
         /// <returns>A combined geometry.</returns>
-        IGeometryImpl CreateCombinedGeometry(GeometryCombineMode combineMode, Geometry g1, Geometry g2);
+        IGeometryImpl CreateCombinedGeometry(GeometryCombineMode combineMode, IGeometryImpl g1, IGeometryImpl g2);
 
         /// <summary>
         /// Created a geometry implementation for the glyph run.

src/Avalonia.Headless/HeadlessPlatformRenderInterface.cs

@@ -47,8 +47,8 @@ namespace Avalonia.Headless
         }
 
         public IStreamGeometryImpl CreateStreamGeometry() => new HeadlessStreamingGeometryStub();
-        public IGeometryImpl CreateGeometryGroup(FillRule fillRule, IReadOnlyList<Geometry> children) => throw new NotImplementedException();
-        public IGeometryImpl CreateCombinedGeometry(GeometryCombineMode combineMode, Geometry g1, Geometry g2) => throw new NotImplementedException();
+        public IGeometryImpl CreateGeometryGroup(FillRule fillRule, IReadOnlyList<IGeometryImpl> children) => throw new NotImplementedException();
+        public IGeometryImpl CreateCombinedGeometry(GeometryCombineMode combineMode, IGeometryImpl g1, IGeometryImpl g2) => throw new NotImplementedException();
 
         public IRenderTarget CreateRenderTarget(IEnumerable<object> surfaces) => new HeadlessRenderTarget();
         public bool IsLost => false;

src/Skia/Avalonia.Skia/CombinedGeometryImpl.cs

@@ -1,4 +1,5 @@
 using Avalonia.Media;
+using Avalonia.Platform;
 using SkiaSharp;
 
 namespace Avalonia.Skia
@@ -15,10 +16,10 @@ namespace Avalonia.Skia
             Bounds = (stroke ?? fill)?.TightBounds.ToAvaloniaRect() ?? default;
         }
 
-        public static CombinedGeometryImpl ForceCreate(GeometryCombineMode combineMode, Geometry g1, Geometry g2)
+        public static CombinedGeometryImpl ForceCreate(GeometryCombineMode combineMode, IGeometryImpl g1, IGeometryImpl g2)
         {
-            if (g1.PlatformImpl is GeometryImpl i1
-                && g2.PlatformImpl is GeometryImpl i2
+            if (g1 is GeometryImpl i1
+                && g2 is GeometryImpl i2
                 && TryCreate(combineMode, i1, i2) is { } result)
                 return result;
             

src/Skia/Avalonia.Skia/GeometryGroupImpl.cs

@@ -1,5 +1,6 @@
 using System.Collections.Generic;
 using Avalonia.Media;
+using Avalonia.Platform;
 using SkiaSharp;
 
 namespace Avalonia.Skia
@@ -9,7 +10,7 @@ namespace Avalonia.Skia
     /// </summary>
     internal class GeometryGroupImpl : GeometryImpl
     {
-        public GeometryGroupImpl(FillRule fillRule, IReadOnlyList<Geometry> children)
+        public GeometryGroupImpl(FillRule fillRule, IReadOnlyList<IGeometryImpl> children)
         {
             var fillType = fillRule == FillRule.NonZero ? SKPathFillType.Winding : SKPathFillType.EvenOdd;
             var count = children.Count;
@@ -22,7 +23,7 @@ namespace Avalonia.Skia
             bool requiresFillPass = false;
             for (var i = 0; i < count; ++i)
             {
-                if (children[i].PlatformImpl is GeometryImpl geo)
+                if (children[i] is GeometryImpl geo)
                 {
                     if (geo.StrokePath != null)
                         stroke.AddPath(geo.StrokePath);
@@ -42,7 +43,7 @@ namespace Avalonia.Skia
 
                 for (var i = 0; i < count; ++i)
                 {
-                    if (children[i].PlatformImpl is GeometryImpl { FillPath: { } fillPath })
+                    if (children[i] is GeometryImpl { FillPath: { } fillPath })
                         fill.AddPath(fillPath);
                 }
 

src/Skia/Avalonia.Skia/PlatformRenderInterface.cs

@@ -58,12 +58,12 @@ namespace Avalonia.Skia
             return new StreamGeometryImpl();
         }
 
-        public IGeometryImpl CreateGeometryGroup(FillRule fillRule, IReadOnlyList<Geometry> children)
+        public IGeometryImpl CreateGeometryGroup(FillRule fillRule, IReadOnlyList<IGeometryImpl> children)
         {
             return new GeometryGroupImpl(fillRule, children);
         }
 
-        public IGeometryImpl CreateCombinedGeometry(GeometryCombineMode combineMode, Geometry g1, Geometry g2)
+        public IGeometryImpl CreateCombinedGeometry(GeometryCombineMode combineMode, IGeometryImpl g1, IGeometryImpl g2)
         {
             return CombinedGeometryImpl.ForceCreate(combineMode, g1, g2);
         }

src/Windows/Avalonia.Direct2D1/Direct2D1Platform.cs

@@ -158,8 +158,8 @@ namespace Avalonia.Direct2D1
         public IGeometryImpl CreateLineGeometry(Point p1, Point p2) => new LineGeometryImpl(p1, p2);
         public IGeometryImpl CreateRectangleGeometry(Rect rect) => new RectangleGeometryImpl(rect);
         public IStreamGeometryImpl CreateStreamGeometry() => new StreamGeometryImpl();
-        public IGeometryImpl CreateGeometryGroup(FillRule fillRule, IReadOnlyList<Geometry> children) => new GeometryGroupImpl(fillRule, children);
-        public IGeometryImpl CreateCombinedGeometry(GeometryCombineMode combineMode, Geometry g1, Geometry g2) => new CombinedGeometryImpl(combineMode, g1, g2);
+        public IGeometryImpl CreateGeometryGroup(FillRule fillRule, IReadOnlyList<IGeometryImpl> children) => new GeometryGroupImpl(fillRule, children);
+        public IGeometryImpl CreateCombinedGeometry(GeometryCombineMode combineMode, IGeometryImpl g1, IGeometryImpl g2) => new CombinedGeometryImpl(combineMode, g1, g2);
 
         public IGlyphRunImpl CreateGlyphRun(IGlyphTypeface glyphTypeface, double fontRenderingEmSize, 
             IReadOnlyList<GlyphInfo> glyphInfos, Point baselineOrigin)

src/Windows/Avalonia.Direct2D1/Media/CombinedGeometryImpl.cs

@@ -1,3 +1,4 @@
+using Avalonia.Platform;
 using SharpDX.Direct2D1;
 using AM = Avalonia.Media;
 
@@ -13,19 +14,19 @@ namespace Avalonia.Direct2D1.Media
         /// </summary>
         public CombinedGeometryImpl(
             AM.GeometryCombineMode combineMode,
-            AM.Geometry geometry1,
-            AM.Geometry geometry2)
+            IGeometryImpl geometry1,
+            IGeometryImpl geometry2)
             : base(CreateGeometry(combineMode, geometry1, geometry2))
         {
         }
 
         private static Geometry CreateGeometry(
             AM.GeometryCombineMode combineMode,
-            AM.Geometry geometry1,
-            AM.Geometry geometry2)
+            IGeometryImpl geometry1,
+            IGeometryImpl geometry2)
         {
-            var g1 = ((GeometryImpl)geometry1.PlatformImpl).Geometry;
-            var g2 = ((GeometryImpl)geometry2.PlatformImpl).Geometry;
+            var g1 = ((GeometryImpl)geometry1).Geometry;
+            var g2 = ((GeometryImpl)geometry2).Geometry;
             var dest = new PathGeometry(Direct2D1Platform.Direct2D1Factory);
             using var sink = dest.Open();
             g1.Combine(g2, (CombineMode)combineMode, sink);

src/Windows/Avalonia.Direct2D1/Media/GeometryGroupImpl.cs

@@ -1,4 +1,5 @@
 using System.Collections.Generic;
+using Avalonia.Platform;
 using SharpDX.Direct2D1;
 using AM = Avalonia.Media;
 
@@ -12,19 +13,19 @@ namespace Avalonia.Direct2D1.Media
         /// <summary>
         /// Initializes a new instance of the <see cref="StreamGeometryImpl"/> class.
         /// </summary>
-        public GeometryGroupImpl(AM.FillRule fillRule, IReadOnlyList<AM.Geometry> geometry)
+        public GeometryGroupImpl(AM.FillRule fillRule, IReadOnlyList<IGeometryImpl> geometry)
             : base(CreateGeometry(fillRule, geometry))
         {
         }
 
-        private static Geometry CreateGeometry(AM.FillRule fillRule, IReadOnlyList<AM.Geometry> children)
+        private static Geometry CreateGeometry(AM.FillRule fillRule, IReadOnlyList<IGeometryImpl> children)
         {
             var count = children.Count;
             var c = new Geometry[count];
 
             for (var i = 0; i < count; ++i)
             {
-                c[i] = ((GeometryImpl)children[i].PlatformImpl).Geometry;
+                c[i] = ((GeometryImpl)children[i]).Geometry;
             }
 
             return new GeometryGroup(Direct2D1Platform.Direct2D1Factory, (FillMode)fillRule, c);

tests/Avalonia.Base.UnitTests/VisualTree/MockRenderInterface.cs

@@ -30,12 +30,12 @@ namespace Avalonia.Base.UnitTests.VisualTree
             return new MockStreamGeometry();
         }
 
-        public IGeometryImpl CreateGeometryGroup(FillRule fillRule, IReadOnlyList<Geometry> children)
+        public IGeometryImpl CreateGeometryGroup(FillRule fillRule, IReadOnlyList<IGeometryImpl> children)
         {
             throw new NotImplementedException();
         }
 
-        public IGeometryImpl CreateCombinedGeometry(GeometryCombineMode combineMode, Geometry g1, Geometry g2)
+        public IGeometryImpl CreateCombinedGeometry(GeometryCombineMode combineMode, IGeometryImpl g1, IGeometryImpl g2)
         {
             throw new NotImplementedException();
         }

tests/Avalonia.Benchmarks/NullRenderingPlatform.cs

@@ -32,12 +32,12 @@ namespace Avalonia.Benchmarks
             return new MockStreamGeometryImpl();
         }
 
-        public IGeometryImpl CreateGeometryGroup(FillRule fillRule, IReadOnlyList<Geometry> children)
+        public IGeometryImpl CreateGeometryGroup(FillRule fillRule, IReadOnlyList<IGeometryImpl> children)
         {
             throw new NotImplementedException();
         }
 
-        public IGeometryImpl CreateCombinedGeometry(GeometryCombineMode combineMode, Geometry g1, Geometry g2)
+        public IGeometryImpl CreateCombinedGeometry(GeometryCombineMode combineMode, IGeometryImpl g1, IGeometryImpl g2)
         {
             throw new NotImplementedException();
         }

tests/Avalonia.UnitTests/MockPlatformRenderInterface.cs

@@ -72,12 +72,12 @@ namespace Avalonia.UnitTests
             return new MockStreamGeometryImpl();
         }
 
-        public IGeometryImpl CreateGeometryGroup(FillRule fillRule, IReadOnlyList<Geometry> children)
+        public IGeometryImpl CreateGeometryGroup(FillRule fillRule, IReadOnlyList<IGeometryImpl> children)
         {
             return Mock.Of<IGeometryImpl>();
         }
 
-        public IGeometryImpl CreateCombinedGeometry(GeometryCombineMode combineMode, Geometry g1, Geometry g2)
+        public IGeometryImpl CreateCombinedGeometry(GeometryCombineMode combineMode, IGeometryImpl g1, IGeometryImpl g2)
         {
             return Mock.Of<IGeometryImpl>();
         }