Ensure IRenderRoot.Renderer is never null

src/Avalonia.Base/Rendering/Composition/CompositingRenderer.cs

@@ -20,15 +20,17 @@ public class CompositingRenderer : IRendererWithCompositor
 {
     private readonly IRenderRoot _root;
     private readonly Compositor _compositor;
-    CompositionDrawingContext _recorder = new();
-    DrawingContext _recordingContext;
-    private HashSet<Visual> _dirty = new();
-    private HashSet<Visual> _recalculateChildren = new();
+    private readonly CompositionDrawingContext _recorder = new();
+    private readonly DrawingContext _recordingContext;
+    private readonly HashSet<Visual> _dirty = new();
+    private readonly HashSet<Visual> _recalculateChildren = new();
+    private readonly Action _update;
+
     private bool _queuedUpdate;
-    private Action _update;
     private bool _updating;
+    private bool _isDisposed;
 
-    internal CompositionTarget CompositionTarget;
+    internal CompositionTarget CompositionTarget { get; }
     
     /// <summary>
     /// Asks the renderer to only draw frames on the render thread. Makes Paint to wait until frame is rendered.
@@ -38,6 +40,17 @@ public class CompositingRenderer : IRendererWithCompositor
     /// <inheritdoc/>
     public RendererDiagnostics Diagnostics { get; }
 
+    /// <inheritdoc />
+    public Compositor Compositor => _compositor;
+
+    /// <summary>
+    /// Initializes a new instance of <see cref="CompositingRenderer"/>
+    /// </summary>
+    /// <param name="root">The render root using this renderer.</param>
+    /// <param name="compositor">The associated compositors.</param>
+    /// <param name="surfaces">
+    /// A function returning the list of native platform's surfaces that can be consumed by rendering subsystems.
+    /// </param>
     public CompositingRenderer(IRenderRoot root, Compositor compositor, Func<IEnumerable<object>> surfaces)
     {
         _root = root;
@@ -66,7 +79,7 @@ public class CompositingRenderer : IRendererWithCompositor
     /// <inheritdoc/>
     public event EventHandler<SceneInvalidatedEventArgs>? SceneInvalidated;
 
-    void QueueUpdate()
+    private void QueueUpdate()
     {
         if(_queuedUpdate)
             return;
@@ -77,9 +90,11 @@ public class CompositingRenderer : IRendererWithCompositor
     /// <inheritdoc/>
     public void AddDirty(Visual visual)
     {
+        if (_isDisposed)
+            return;
         if (_updating)
             throw new InvalidOperationException("Visual was invalidated during the render pass");
-        _dirty.Add((Visual)visual);
+        _dirty.Add(visual);
         QueueUpdate();
     }
 
@@ -126,9 +141,11 @@ public class CompositingRenderer : IRendererWithCompositor
     /// <inheritdoc/>
     public void RecalculateChildren(Visual visual)
     {
+        if (_isDisposed)
+            return;
         if (_updating)
             throw new InvalidOperationException("Visual was invalidated during the render pass");
-        _recalculateChildren.Add((Visual)visual);
+        _recalculateChildren.Add(visual);
         QueueUpdate();
     }
 
@@ -171,7 +188,7 @@ public class CompositingRenderer : IRendererWithCompositor
             if (sortedChildren != null)
                 for (var c = 0; c < visualChildren.Count; c++)
                 {
-                    if (!ReferenceEquals(compositionChildren[c], ((Visual)sortedChildren[c].visual).CompositionVisual))
+                    if (!ReferenceEquals(compositionChildren[c], sortedChildren[c].visual.CompositionVisual))
                     {
                         mismatch = true;
                         break;
@@ -179,7 +196,7 @@ public class CompositingRenderer : IRendererWithCompositor
                 }
             else
                 for (var c = 0; c < visualChildren.Count; c++)
-                    if (!ReferenceEquals(compositionChildren[c], ((Visual)visualChildren[c]).CompositionVisual))
+                    if (!ReferenceEquals(compositionChildren[c], visualChildren[c].CompositionVisual))
                     {
                         mismatch = true;
                         break;
@@ -201,7 +218,7 @@ public class CompositingRenderer : IRendererWithCompositor
         {
             foreach (var ch in sortedChildren)
             {
-                var compositionChild = ((Visual)ch.visual).CompositionVisual;
+                var compositionChild = ch.visual.CompositionVisual;
                 if (compositionChild != null)
                     compositionChildren.Add(compositionChild);
             }
@@ -210,7 +227,7 @@ public class CompositingRenderer : IRendererWithCompositor
         else
             foreach (var ch in v.GetVisualChildren())
             {
-                var compositionChild = ((Visual)ch).CompositionVisual;
+                var compositionChild = ch.CompositionVisual;
                 if (compositionChild != null)
                     compositionChildren.Add(compositionChild);
             }
@@ -289,13 +306,18 @@ public class CompositingRenderer : IRendererWithCompositor
             _updating = false;
         }
     }
-    
+
+    /// <inheritdoc />
     public void Resized(Size size)
     {
     }
 
+    /// <inheritdoc />
     public void Paint(Rect rect)
     {
+        if (_isDisposed)
+            return;
+
         QueueUpdate();
         CompositionTarget.RequestRedraw();
         if(RenderOnlyOnRenderThread && Compositor.Loop.RunsInBackground)
@@ -304,17 +326,34 @@ public class CompositingRenderer : IRendererWithCompositor
             CompositionTarget.ImmediateUIThreadRender();
     }
 
-    public void Start() => CompositionTarget.IsEnabled = true;
-
-    public void Stop()
+    /// <inheritdoc />
+    public void Start()
     {
-        CompositionTarget.IsEnabled = false;
+        if (_isDisposed)
+            return;
+
+        CompositionTarget.IsEnabled = true;
     }
 
-    public ValueTask<object?> TryGetRenderInterfaceFeature(Type featureType) => Compositor.TryGetRenderInterfaceFeature(featureType);
+    /// <inheritdoc />
+    public void Stop()
+        => CompositionTarget.IsEnabled = false;
+
+    /// <inheritdoc />
+    public ValueTask<object?> TryGetRenderInterfaceFeature(Type featureType)
+        => Compositor.TryGetRenderInterfaceFeature(featureType);
 
+    /// <inheritdoc />
     public void Dispose()
     {
+        if (_isDisposed)
+            return;
+
+        _isDisposed = true;
+        _dirty.Clear();
+        _recalculateChildren.Clear();
+        SceneInvalidated = null;
+
         Stop();
         CompositionTarget.Dispose();
         
@@ -323,9 +362,4 @@ public class CompositingRenderer : IRendererWithCompositor
         if (Compositor.Loop.RunsInBackground)
             _compositor.Commit().Wait();
     }
-
-    /// <summary>
-    /// The associated <see cref="Avalonia.Rendering.Composition.Compositor"/> object
-    /// </summary>
-    public Compositor Compositor => _compositor;
 }

src/Avalonia.Base/Rendering/IRenderRoot.cs

@@ -1,6 +1,4 @@
 using Avalonia.Metadata;
-using Avalonia.Platform;
-using Avalonia.VisualTree;
 
 namespace Avalonia.Rendering
 {

src/Avalonia.Base/Rendering/IRenderer.cs

@@ -90,6 +90,9 @@ namespace Avalonia.Rendering
     
     public interface IRendererWithCompositor : IRenderer
     {
+        /// <summary>
+        /// The associated <see cref="Avalonia.Rendering.Composition.Compositor"/> object
+        /// </summary>
         Compositor Compositor { get; }
     }
 }

src/Avalonia.Base/Visual.cs

@@ -348,7 +348,7 @@ namespace Avalonia
         /// </summary>
         public void InvalidateVisual()
         {
-            VisualRoot?.Renderer?.AddDirty(this);
+            VisualRoot?.Renderer.AddDirty(this);
         }
 
         /// <summary>
@@ -449,7 +449,7 @@ namespace Avalonia
         protected override void LogicalChildrenCollectionChanged(object? sender, NotifyCollectionChangedEventArgs e)
         {
             base.LogicalChildrenCollectionChanged(sender, e);
-            VisualRoot?.Renderer?.RecalculateChildren(this);
+            VisualRoot?.Renderer.RecalculateChildren(this);
         }
 
         /// <summary>
@@ -477,7 +477,7 @@ namespace Avalonia
             OnAttachedToVisualTree(e);
             AttachedToVisualTree?.Invoke(this, e);
             InvalidateVisual();
-            _visualRoot.Renderer?.RecalculateChildren(_visualParent!);
+            _visualRoot.Renderer.RecalculateChildren(_visualParent!);
 
             if (ZIndex != 0 && VisualParent is Visual parent)
                 parent.HasNonUniformZIndexChildren = true;
@@ -540,7 +540,7 @@ namespace Avalonia
             }
 
             DetachedFromVisualTree?.Invoke(this, e);
-            e.Root?.Renderer?.AddDirty(this);
+            e.Root.Renderer.AddDirty(this);
 
             var visualChildren = VisualChildren;
 
@@ -659,7 +659,7 @@ namespace Avalonia
                 parentVisual.HasNonUniformZIndexChildren = true;
             
             sender?.InvalidateVisual();
-            parent?.VisualRoot?.Renderer?.RecalculateChildren(parent);
+            parent?.VisualRoot?.Renderer.RecalculateChildren(parent);
         }
 
         /// <summary>

src/Avalonia.Controls/TopLevel.cs

@@ -94,7 +94,6 @@ namespace Avalonia.Controls
         private readonly IInputManager? _inputManager;
         private readonly IAccessKeyHandler? _accessKeyHandler;
         private readonly IKeyboardNavigationHandler? _keyboardNavigationHandler;
-        private readonly IPlatformRenderInterface? _renderInterface;
         private readonly IGlobalStyles? _globalStyles;
         private readonly IGlobalThemeVariantProvider? _applicationThemeHost;
         private readonly PointerOverPreProcessor? _pointerOverPreProcessor;
@@ -136,36 +135,21 @@ namespace Avalonia.Controls
         /// </param>
         public TopLevel(ITopLevelImpl impl, IAvaloniaDependencyResolver? dependencyResolver)
         {
-            if (impl == null)
-            {
-                throw new InvalidOperationException(
-                    "Could not create window implementation: maybe no windowing subsystem was initialized?");
-            }
-
-            PlatformImpl = impl;
+            PlatformImpl = impl ?? throw new InvalidOperationException(
+                "Could not create window implementation: maybe no windowing subsystem was initialized?");
 
             _actualTransparencyLevel = PlatformImpl.TransparencyLevel;            
 
-            dependencyResolver = dependencyResolver ?? AvaloniaLocator.Current;
+            dependencyResolver ??= AvaloniaLocator.Current;
 
             _accessKeyHandler = TryGetService<IAccessKeyHandler>(dependencyResolver);
             _inputManager = TryGetService<IInputManager>(dependencyResolver);
             _keyboardNavigationHandler = TryGetService<IKeyboardNavigationHandler>(dependencyResolver);
-            _renderInterface = TryGetService<IPlatformRenderInterface>(dependencyResolver);
             _globalStyles = TryGetService<IGlobalStyles>(dependencyResolver);
             _applicationThemeHost = TryGetService<IGlobalThemeVariantProvider>(dependencyResolver);
 
             Renderer = impl.CreateRenderer(this);
-
-            if (Renderer != null)
-            {
-                Renderer.SceneInvalidated += SceneInvalidated;
-            }
-            else
-            {
-                // Prevent nullable error.
-                Renderer = null!;
-            }
+            Renderer.SceneInvalidated += SceneInvalidated;
 
             impl.SetInputRoot(this);
 
@@ -216,7 +200,7 @@ namespace Avalonia.Controls
 
             if(impl.TryGetFeature<ISystemNavigationManagerImpl>() is {} systemNavigationManager)
             {
-                systemNavigationManager.BackRequested += (s, e) =>
+                systemNavigationManager.BackRequested += (_, e) =>
                 {
                     e.RoutedEvent = BackRequestedEvent;
                     RaiseEvent(e);
@@ -337,7 +321,7 @@ namespace Avalonia.Controls
                 {
                     _layoutManager = CreateLayoutManager();
 
-                    if (_layoutManager is LayoutManager typedLayoutManager && Renderer is not null)
+                    if (_layoutManager is LayoutManager typedLayoutManager)
                     {
                         _layoutDiagnosticBridge = new LayoutDiagnosticBridge(Renderer.Diagnostics, typedLayoutManager);
                         _layoutDiagnosticBridge.SetupBridge();
@@ -356,7 +340,7 @@ namespace Avalonia.Controls
         /// <summary>
         /// Gets the renderer for the window.
         /// </summary>
-        public IRenderer Renderer { get; private set; }
+        public IRenderer Renderer { get; }
 
         internal PixelPoint? LastPointerPosition => _pointerOverPreProcessor?.LastPosition;
         
@@ -450,7 +434,7 @@ namespace Avalonia.Controls
         /// <param name="rect">The dirty area.</param>
         protected virtual void HandlePaint(Rect rect)
         {
-            Renderer?.Paint(rect);
+            Renderer.Paint(rect);
         }
 
         /// <summary>
@@ -468,8 +452,8 @@ namespace Avalonia.Controls
                 _applicationThemeHost.ActualThemeVariantChanged -= GlobalActualThemeVariantChanged;
             }
 
-            Renderer?.Dispose();
-            Renderer = null!;
+            Renderer.SceneInvalidated -= SceneInvalidated;
+            Renderer.Dispose();
 
             _layoutDiagnosticBridge?.Dispose();
             _layoutDiagnosticBridge = null;
@@ -488,7 +472,7 @@ namespace Avalonia.Controls
             
             OnClosed(EventArgs.Empty);
 
-            LayoutManager?.Dispose();
+            LayoutManager.Dispose();
         }
 
         /// <summary>
@@ -503,7 +487,7 @@ namespace Avalonia.Controls
             Width = clientSize.Width;
             Height = clientSize.Height;
             LayoutManager.ExecuteLayoutPass();
-            Renderer?.Resized(clientSize);
+            Renderer.Resized(clientSize);
         }
 
         /// <summary>

src/Avalonia.Controls/Window.cs

@@ -573,7 +573,7 @@ namespace Avalonia.Controls
                     return;
                 }
 
-                Renderer?.Stop();
+                Renderer.Stop();
 
                 if (Owner is Window owner)
                 {
@@ -721,7 +721,7 @@ namespace Avalonia.Controls
                 SetWindowStartupLocation(owner?.PlatformImpl);
 
                 PlatformImpl?.Show(ShowActivated, false);
-                Renderer?.Start();
+                Renderer.Start();
                 OnOpened(EventArgs.Empty);
             }
         }
@@ -798,7 +798,7 @@ namespace Avalonia.Controls
 
                 PlatformImpl?.Show(ShowActivated, true);
 
-                Renderer?.Start();
+                Renderer.Start();
 
                 Observable.FromEventPattern(
                         x => Closed += x,

src/Avalonia.Controls/WindowBase.cs

@@ -129,7 +129,7 @@ namespace Avalonia.Controls
         {
             using (FreezeVisibilityChangeHandling())
             {
-                Renderer?.Stop();
+                Renderer.Stop();
                 PlatformImpl?.Hide();
                 IsVisible = false;
             }
@@ -153,7 +153,7 @@ namespace Avalonia.Controls
                 }
 
                 PlatformImpl?.Show(true, false);
-                Renderer?.Start();
+                Renderer.Start();
                 OnOpened(EventArgs.Empty);
             }
         }
@@ -219,7 +219,7 @@ namespace Avalonia.Controls
             {
                 ClientSize = clientSize;
                 LayoutManager.ExecuteLayoutPass();
-                Renderer?.Resized(clientSize);
+                Renderer.Resized(clientSize);
             }
         }
 

src/Avalonia.Diagnostics/Diagnostics/Controls/Application.cs

@@ -33,7 +33,7 @@ namespace Avalonia.Diagnostics.Controls
             RendererRoot = application.ApplicationLifetime switch
             {
                 Lifetimes.IClassicDesktopStyleApplicationLifetime classic => classic.MainWindow?.Renderer,
-                Lifetimes.ISingleViewApplicationLifetime single => (single.MainView as Visual)?.VisualRoot?.Renderer,
+                Lifetimes.ISingleViewApplicationLifetime single => single.MainView?.VisualRoot?.Renderer,
                 _ => null
             };
 

src/Avalonia.Native/WindowImpl.cs

@@ -119,7 +119,8 @@ namespace Avalonia.Native
             {
                 if(e.Type == RawPointerEventType.LeftButtonDown)
                 {
-                    var visual = (_inputRoot as Window).Renderer.HitTestFirst(e.Position, _inputRoot as Window, x =>
+                    var window = _inputRoot as Window;
+                    var visual = window?.Renderer.HitTestFirst(e.Position, window, x =>
                             {
                                 if (x is IInputElement ie && (!ie.IsHitTestVisible || !ie.IsEffectivelyVisible))
                                 {

tests/Avalonia.Controls.UnitTests/ButtonTests.cs

@@ -140,10 +140,9 @@ namespace Avalonia.Controls.UnitTests
                 .Returns<Point, Visual, Func<Visual, bool>>((p, r, f) =>
                     r.Bounds.Contains(p) ? new Visual[] { r } : new Visual[0]);
 
-            var target = new TestButton()
+            var target = new TestButton(renderer.Object)
             {
-                Bounds = new Rect(0, 0, 100, 100),
-                Renderer = renderer.Object
+                Bounds = new Rect(0, 0, 100, 100)
             };
 
             bool clicked = false;
@@ -172,10 +171,9 @@ namespace Avalonia.Controls.UnitTests
                 .Returns<Point, Visual, Func<Visual, bool>>((p, r, f) =>
                     r.Bounds.Contains(p) ? new Visual[] { r } : new Visual[0]);
 
-            var target = new TestButton()
+            var target = new TestButton(renderer.Object)
             {
-                Bounds = new Rect(0, 0, 100, 100),
-                Renderer = renderer.Object
+                Bounds = new Rect(0, 0, 100, 100)
             };
 
             bool clicked = false;
@@ -206,11 +204,10 @@ namespace Avalonia.Controls.UnitTests
                     r.Bounds.Contains(p.Transform(r.RenderTransform.Value.Invert())) ?
                     new Visual[] { r } : new Visual[0]);
 
-            var target = new TestButton()
+            var target = new TestButton(renderer.Object)
             {
                 Bounds = new Rect(0, 0, 100, 100),
-                RenderTransform = new TranslateTransform { X = 100, Y = 0 },
-                Renderer = renderer.Object
+                RenderTransform = new TranslateTransform { X = 100, Y = 0 }
             };
 
             //actual bounds of button should  be 100,0,100,100 x -> translated 100 pixels
@@ -386,9 +383,10 @@ namespace Avalonia.Controls.UnitTests
 
         private class TestButton : Button, IRenderRoot
         {
-            public TestButton()
+            public TestButton(IRenderer renderer)
             {
                 IsVisible = true;
+                Renderer = renderer;
             }
 
             public new Rect Bounds
@@ -399,7 +397,7 @@ namespace Avalonia.Controls.UnitTests
 
             public Size ClientSize => throw new NotImplementedException();
 
-            public IRenderer Renderer { get; set; }
+            public IRenderer Renderer { get; }
 
             public double RenderScaling => throw new NotImplementedException();
 

tests/Avalonia.Controls.UnitTests/TopLevelTests.cs

@@ -6,6 +6,7 @@ using Avalonia.Input.Raw;
 using Avalonia.Layout;
 using Avalonia.LogicalTree;
 using Avalonia.Platform;
+using Avalonia.Rendering;
 using Avalonia.Styling;
 using Avalonia.UnitTests;
 using Moq;
@@ -20,7 +21,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var impl = new Mock<ITopLevelImpl>();
+                var impl = CreateMockTopLevelImpl();
                 var target = new TestTopLevel(impl.Object);
 
                 Assert.True(((ILogical)target).IsAttachedToLogicalTree);
@@ -32,7 +33,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var impl = new Mock<ITopLevelImpl>();
+                var impl = CreateMockTopLevelImpl();
                 impl.Setup(x => x.ClientSize).Returns(new Size(123, 456));
 
                 var target = new TestTopLevel(impl.Object);
@@ -46,7 +47,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var impl = new Mock<ITopLevelImpl>();
+                var impl = CreateMockTopLevelImpl();
                 impl.Setup(x => x.ClientSize).Returns(new Size(123, 456));
 
                 var target = new TestTopLevel(impl.Object);
@@ -60,7 +61,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var impl = new Mock<ITopLevelImpl>();
+                var impl = CreateMockTopLevelImpl();
                 impl.Setup(x => x.ClientSize).Returns(new Size(123, 456));
 
                 var target = new TestTopLevel(impl.Object);
@@ -76,7 +77,7 @@ namespace Avalonia.Controls.UnitTests
 
             using (UnitTestApplication.Start(services))
             {
-                var impl = new Mock<ITopLevelImpl>();
+                var impl = CreateMockTopLevelImpl();
                 
                 var target = new TestTopLevel(impl.Object, Mock.Of<ILayoutManager>());
 
@@ -91,7 +92,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var impl = new Mock<ITopLevelImpl>();
+                var impl = CreateMockTopLevelImpl();
                 impl.SetupProperty(x => x.Resized);
                 impl.SetupGet(x => x.RenderScaling).Returns(1);
 
@@ -117,7 +118,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var impl = new Mock<ITopLevelImpl>();
+                var impl = CreateMockTopLevelImpl();
                 impl.Setup(x => x.ClientSize).Returns(new Size(123, 456));
 
                 var target = new TestTopLevel(impl.Object);
@@ -133,7 +134,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var impl = new Mock<ITopLevelImpl>();
+                var impl = CreateMockTopLevelImpl();
                 impl.SetupAllProperties();
                 impl.Setup(x => x.ClientSize).Returns(new Size(123, 456));
 
@@ -151,7 +152,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var impl = new Mock<ITopLevelImpl>();
+                var impl = CreateMockTopLevelImpl();
                 impl.SetupAllProperties();
 
                 bool raised = false;
@@ -169,7 +170,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var impl = new Mock<ITopLevelImpl>();
+                var impl = CreateMockTopLevelImpl();
                 impl.SetupAllProperties();
 
                 var target = new TestTopLevel(impl.Object);
@@ -200,7 +201,7 @@ namespace Avalonia.Controls.UnitTests
 
             using (UnitTestApplication.Start(services))
             {
-                var impl = new Mock<ITopLevelImpl>();
+                var impl = CreateMockTopLevelImpl();
                 impl.SetupAllProperties();
 
                 var target = new TestTopLevel(impl.Object);
@@ -222,7 +223,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var impl = new Mock<ITopLevelImpl>();
+                var impl = CreateMockTopLevelImpl();
                 impl.SetupAllProperties();
                 var target = new TestTopLevel(impl.Object);
                 var child = new TestTopLevel(impl.Object);
@@ -240,7 +241,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var impl = new Mock<ITopLevelImpl>();
+                var impl = CreateMockTopLevelImpl();
                 impl.SetupAllProperties();
                 var target = new TestTopLevel(impl.Object);
                 var raised = false;
@@ -257,7 +258,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var impl = new Mock<ITopLevelImpl>();
+                var impl = CreateMockTopLevelImpl();
                 impl.SetupAllProperties();
 
                 var layoutManager = new Mock<ILayoutManager>();
@@ -274,7 +275,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var impl = new Mock<ITopLevelImpl>();
+                var impl = CreateMockTopLevelImpl();
                 impl.SetupGet(x => x.RenderScaling).Returns(1);
 
                 var child = new Border { Classes = { "foo" } };
@@ -317,6 +318,14 @@ namespace Avalonia.Controls.UnitTests
                 }.RegisterInNameScope(scope));
         }
 
+        private static Mock<ITopLevelImpl> CreateMockTopLevelImpl()
+        {
+            var renderer = new Mock<ITopLevelImpl>();
+            renderer.Setup(r => r.CreateRenderer(It.IsAny<IRenderRoot>()))
+                .Returns(RendererMocks.CreateRenderer().Object);
+            return renderer;
+        }
+
         private class TestTopLevel : TopLevel
         {
             private readonly ILayoutManager _layoutManager;

tests/Avalonia.Controls.UnitTests/Utils/HotKeyManagerTests.cs

@@ -4,9 +4,7 @@ using Avalonia.Controls.Templates;
 using Avalonia.Input;
 using Avalonia.Input.Raw;
 using Avalonia.Platform;
-using Avalonia.Styling;
 using Avalonia.UnitTests;
-using Moq;
 using Xunit;
 using Factory = System.Func<int, System.Action<object>, Avalonia.Controls.Window, Avalonia.AvaloniaObject>;
 
@@ -20,7 +18,7 @@ namespace Avalonia.Controls.UnitTests.Utils
             using (AvaloniaLocator.EnterScope())
             {
                 AvaloniaLocator.CurrentMutable
-                    .Bind<IWindowingPlatform>().ToConstant(new WindowingPlatformMock());
+                    .Bind<IWindowingPlatform>().ToConstant(new MockWindowingPlatform());
 
                 var gesture1 = new KeyGesture(Key.A, KeyModifiers.Control);
                 var gesture2 = new KeyGesture(Key.B, KeyModifiers.Control);
@@ -64,7 +62,7 @@ namespace Avalonia.Controls.UnitTests.Utils
                 var commandResult = 0;
                 var expectedParameter = 1;
                 AvaloniaLocator.CurrentMutable
-                    .Bind<IWindowingPlatform>().ToConstant(new WindowingPlatformMock());
+                    .Bind<IWindowingPlatform>().ToConstant(new MockWindowingPlatform());
 
                 var gesture = new KeyGesture(Key.A, KeyModifiers.Control);
 
@@ -106,7 +104,7 @@ namespace Avalonia.Controls.UnitTests.Utils
                 var target = new KeyboardDevice();
                 var isExecuted = false;
                 AvaloniaLocator.CurrentMutable
-                    .Bind<IWindowingPlatform>().ToConstant(new WindowingPlatformMock());
+                    .Bind<IWindowingPlatform>().ToConstant(new MockWindowingPlatform());
 
                 var gesture = new KeyGesture(Key.A, KeyModifiers.Control);
 
@@ -146,7 +144,7 @@ namespace Avalonia.Controls.UnitTests.Utils
                 var target = new KeyboardDevice();
                 var clickExecutedCount = 0;
                 AvaloniaLocator.CurrentMutable
-                    .Bind<IWindowingPlatform>().ToConstant(new WindowingPlatformMock());
+                    .Bind<IWindowingPlatform>().ToConstant(new MockWindowingPlatform());
 
                 var gesture = new KeyGesture(Key.A, KeyModifiers.Control);
 
@@ -199,7 +197,7 @@ namespace Avalonia.Controls.UnitTests.Utils
                 var clickExecutedCount = 0;
                 var commandExecutedCount = 0;
                 AvaloniaLocator.CurrentMutable
-                    .Bind<IWindowingPlatform>().ToConstant(new WindowingPlatformMock());
+                    .Bind<IWindowingPlatform>().ToConstant(new MockWindowingPlatform());
 
                 var gesture = new KeyGesture(Key.A, KeyModifiers.Control);
 

tests/Avalonia.Controls.UnitTests/WindowBaseTests.cs

@@ -22,7 +22,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var impl = new Mock<IWindowBaseImpl>();
+                var impl = CreateMockWindowBaseImpl();
                 var target = new TestWindowBase(impl.Object);
 
                 target.Activate();
@@ -36,7 +36,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var impl = new Mock<IWindowBaseImpl>();
+                var impl = CreateMockWindowBaseImpl();
                 impl.SetupAllProperties();
 
                 bool raised = false;
@@ -55,7 +55,7 @@ namespace Avalonia.Controls.UnitTests
         {
             using (UnitTestApplication.Start(TestServices.StyledWindow))
             {
-                var impl = new Mock<IWindowBaseImpl>();
+                var impl = CreateMockWindowBaseImpl();
                 impl.SetupAllProperties();
 
                 bool raised = false;
@@ -241,6 +241,14 @@ namespace Avalonia.Controls.UnitTests
                 }.RegisterInNameScope(scope));
         }
 
+        private static Mock<IWindowBaseImpl> CreateMockWindowBaseImpl()
+        {
+            var renderer = new Mock<IWindowBaseImpl>();
+            renderer.Setup(r => r.CreateRenderer(It.IsAny<IRenderRoot>()))
+                .Returns(RendererMocks.CreateRenderer().Object);
+            return renderer;
+        }
+
         private class TestWindowBase : WindowBase
         {
             public bool IsClosed { get; private set; }

tests/Avalonia.Controls.UnitTests/WindowTests.cs

@@ -15,6 +15,8 @@ namespace Avalonia.Controls.UnitTests
         public void Setting_Title_Should_Set_Impl_Title()
         {
             var windowImpl = new Mock<IWindowImpl>();
+            windowImpl.Setup(r => r.CreateRenderer(It.IsAny<IRenderRoot>()))
+                .Returns(RendererMocks.CreateRenderer().Object);
             var windowingPlatform = new MockWindowingPlatform(() => windowImpl.Object);
 
             using (UnitTestApplication.Start(new TestServices(windowingPlatform: windowingPlatform)))

tests/Avalonia.Controls.UnitTests/WindowingPlatformMock.cs

@@ -1,35 +0,0 @@
-using System;
-using Moq;
-using Avalonia.Platform;
-
-namespace Avalonia.Controls.UnitTests
-{
-    public class WindowingPlatformMock : IWindowingPlatform
-    {
-        private readonly Func<IWindowImpl> _windowImpl;
-        private readonly Func<IPopupImpl> _popupImpl;
-
-        public WindowingPlatformMock(Func<IWindowImpl> windowImpl = null, Func<IPopupImpl> popupImpl = null )
-        {
-            _windowImpl = windowImpl;
-            _popupImpl = popupImpl;
-        }
-
-        public IWindowImpl CreateWindow()
-        {
-            return _windowImpl?.Invoke() ?? Mock.Of<IWindowImpl>(x => x.RenderScaling == 1);
-        }
-
-        public IWindowImpl CreateEmbeddableWindow()
-        {
-            throw new NotImplementedException();
-        }
-
-        public ITrayIconImpl CreateTrayIcon()
-        {
-            return null;
-        }
-
-        public IPopupImpl CreatePopup() => _popupImpl?.Invoke() ?? Mock.Of<IPopupImpl>(x => x.RenderScaling == 1);
-    }
-}

tests/Avalonia.UnitTests/TestTemplatedRoot.cs

@@ -1,54 +0,0 @@
-using System;
-using Avalonia.Controls;
-using Avalonia.Controls.Presenters;
-using Avalonia.Controls.Templates;
-using Avalonia.Layout;
-using Avalonia.LogicalTree;
-using Avalonia.Platform;
-using Avalonia.Rendering;
-using Avalonia.Styling;
-
-namespace Avalonia.UnitTests
-{
-    public class TestTemplatedRoot : ContentControl, ILayoutRoot, IRenderRoot, ILogicalRoot
-    {
-        private readonly NameScope _nameScope = new NameScope();
-
-        public TestTemplatedRoot()
-        {
-            LayoutManager = new LayoutManager(this);
-            Template = new FuncControlTemplate<TestTemplatedRoot>((x, scope) => new ContentPresenter
-            {
-                Name = "PART_ContentPresenter",
-            }.RegisterInNameScope(scope));
-        }
-
-        public Size ClientSize => new Size(100, 100);
-
-        public Size MaxClientSize => Size.Infinity;
-
-        public double LayoutScaling => 1;
-
-        public ILayoutManager LayoutManager { get; set; }
-
-        public double RenderScaling => 1;
-
-        public IRenderTarget RenderTarget => null;
-
-        public IRenderer Renderer => null;
-
-        public IRenderTarget CreateRenderTarget()
-        {
-            throw new NotImplementedException();
-        }
-
-        public void Invalidate(Rect rect)
-        {
-            throw new NotImplementedException();
-        }
-
-        public Point PointToClient(PixelPoint p) => p.ToPoint(1);
-
-        public PixelPoint PointToScreen(Point p) => PixelPoint.FromPoint(p, 1);
-    }
-}