Media system refactoring

- animation/layout/render cycle is now managed from a central location
- animations are now throttled if animation/layout/render pass takes longer than a frame which previously caused a soft-freeze with input not being processed
- the public API is trimmed to make sure that we can make other planned changes during the 11.x support cycle

"Changelog":
- IClock is hidden and is planned to be replaced later
- Animator classes are hidden and are planned to be refactored later
- IAnimation members are hidden, it's supposed to be a marker interface for Style.Animations collection now, to start animations manually use Animation.RunAsync
- Sealed several classes in Avalonia.Animation namespace
- Spring class is removed from the public API (it wasn't possible to use it directly in a meaningful way anyway)
- Sealed brushes, transforms, effects and drawings
- Removed separate dispatcher priorities for Layout and Composition, everything now happens from a central place with Render priority (same as WPF)
- - some private "hook" priorities are added for now, those will be removed later
- IRenderLoop is hidden and removed from locator
- IRenderer is hidden (the plan is to remove that concept later)
- - Renderer.Start/Stop exposed as StartRendering/StopRendering on the toplevel (will be on a CompositionTarget/PresentationSource-like type later)
- - Renderer.Diagnistics exposed as RendererDiagnostics (same)
- - Renderer is no longer created by the platform code and is created by TopLevel itself
- - From the user-code hit-testing should be done by VisualExtensions.GetVisual(s)At, which has the same features
- - For unit tests a separate IHitTester interface is added which can be changed for a particular toplevel
- ILayoutManager is hidden
- - LayoutManager.ExecuteLayoutPass() exposed as TopLevel.UpdateLayout()
- Custom animators now have a separate base class that only deals with interpolation

Minor improvements:
- Compositor has a mode that doesn't use DispatcherTimers, useful for unit tests
- Introduced ScopedTestBase that auto-resets the locator when test is finished

nukebuild/RefAssemblyGenerator.cs

@@ -71,10 +71,10 @@ public class RefAssemblyGenerator
         foreach (var nested in type.NestedTypes)
             ProcessType(nested, obsoleteCtor);
 
-        var hideMethods = (type.IsInterface && type.Name.EndsWith("Impl"))
+        var hideMembers = (type.IsInterface && type.Name.EndsWith("Impl"))
                           || HasPrivateApi(type.CustomAttributes);
 
-        var injectMethod = hideMethods
+        var injectMethod = hideMembers
                            || type.CustomAttributes.Any(a =>
                                a.AttributeType.FullName == "Avalonia.Metadata.NotClientImplementableAttribute");
 
@@ -95,21 +95,47 @@ public class RefAssemblyGenerator
 
         foreach (var m in type.Methods)
         {
-            if (hideMethods || HasPrivateApi(m.CustomAttributes))
+            if (hideMembers || HasPrivateApi(m.CustomAttributes))
             {
-                var dflags = MethodAttributes.Public | MethodAttributes.Family | MethodAttributes.FamORAssem |
-                             MethodAttributes.FamANDAssem | MethodAttributes.Assembly;
-                m.Attributes = ((m.Attributes | dflags) ^ dflags) | MethodAttributes.Assembly;
+                HideMethod(m);
             }
             MarkAsUnstable(m, obsoleteCtor, forceUnstable);
         }
 
+        foreach (var p in type.Properties)
+        {
+            if (HasPrivateApi(p.CustomAttributes))
+            {
+                if (p.SetMethod != null)
+                    HideMethod(p.SetMethod);
+                if (p.GetMethod != null)
+                    HideMethod(p.GetMethod);
+            }
+        }
+
+        foreach (var f in type.Fields)
+        {
+            if (hideMembers || HasPrivateApi(f.CustomAttributes))
+            {
+                var dflags = FieldAttributes.Public | FieldAttributes.Family | FieldAttributes.FamORAssem |
+                             FieldAttributes.FamANDAssem | FieldAttributes.Assembly;
+                f.Attributes = ((f.Attributes | dflags) ^ dflags) | FieldAttributes.Assembly;
+            }
+        }
+
         foreach (var m in type.Properties)
             MarkAsUnstable(m, obsoleteCtor, forceUnstable);
         foreach (var m in type.Events)
             MarkAsUnstable(m, obsoleteCtor, forceUnstable);
     }
 
+    static void HideMethod(MethodDefinition m)
+    {
+        var dflags = MethodAttributes.Public | MethodAttributes.Family | MethodAttributes.FamORAssem |
+                     MethodAttributes.FamANDAssem | MethodAttributes.Assembly;
+        m.Attributes = ((m.Attributes | dflags) ^ dflags) | MethodAttributes.Assembly;
+    }
+    
     static void MarkAsUnstable(IMemberDefinition def, MethodReference obsoleteCtor, ICustomAttribute unstableAttribute)
     {
         if (def.CustomAttributes.Any(a => a.AttributeType.FullName == "System.ObsoleteAttribute"))

samples/ControlCatalog/Pages/ItemsRepeaterPage.xaml.cs

@@ -117,9 +117,8 @@ namespace ControlCatalog.Pages
         private void ScrollTo(int index)
         {
             System.Diagnostics.Debug.WriteLine("Scroll to " + index);
-            var layoutManager = ((TopLevel)VisualRoot!).LayoutManager;
             var element = _repeater.GetOrCreateElement(index);
-            layoutManager.ExecuteLayoutPass();
+            ((TopLevel)VisualRoot!).UpdateLayout();
             element.BringIntoView();
         }
 

samples/GpuInterop/MainWindow.axaml.cs

@@ -11,7 +11,7 @@ namespace GpuInterop
         {
             InitializeComponent();
             this.AttachDevTools();
-            Renderer.Diagnostics.DebugOverlays = RendererDebugOverlays.Fps;
+            RendererDiagnostics.DebugOverlays = RendererDebugOverlays.Fps;
         }
 
         private void InitializeComponent()

samples/RenderDemo/MainWindow.xaml.cs

@@ -21,7 +21,7 @@ namespace RenderDemo
             void BindOverlay(Expression<Func<MainWindowViewModel, bool>> expr, RendererDebugOverlays overlay)
                 => vm.WhenAnyValue(expr).Subscribe(x =>
                 {
-                    var diagnostics = Renderer.Diagnostics;
+                    var diagnostics = RendererDiagnostics;
                     diagnostics.DebugOverlays = x ?
                         diagnostics.DebugOverlays | overlay :
                         diagnostics.DebugOverlays & ~overlay;

samples/RenderDemo/Pages/AnimationsPage.xaml

@@ -347,12 +347,8 @@
   </UserControl.Styles>
   <Grid>
     <StackPanel HorizontalAlignment="Center" VerticalAlignment="Center" ClipToBounds="False">
-      <StackPanel.Clock>
-        <Clock />
-      </StackPanel.Clock>
       <StackPanel Orientation="Horizontal" VerticalAlignment="Center" Spacing="20">
         <TextBlock VerticalAlignment="Center">Hover to activate Keyframe Animations.</TextBlock>
-        <Button Content="{Binding PlayStateText}" Command="{Binding TogglePlayState}" Click="ToggleClock" />
       </StackPanel>
       <WrapPanel ClipToBounds="False">
         <Border Classes="Test Rect1" Background="DarkRed"/>

samples/RenderDemo/Pages/AnimationsPage.xaml.cs

@@ -24,20 +24,5 @@ namespace RenderDemo.Pages
         {
             AvaloniaXamlLoader.Load(this);
         }
-
-        private void ToggleClock(object sender, RoutedEventArgs args)
-        {
-            var button = sender as Button;
-            var clock = button.Clock;
-
-            if (clock.PlayState == PlayState.Run)
-            {
-                clock.PlayState = PlayState.Pause;
-            }
-            else if (clock.PlayState == PlayState.Pause)
-            {
-                clock.PlayState = PlayState.Run;
-            }
-        }
     }
 }

samples/RenderDemo/Pages/CustomAnimatorPage.xaml

@@ -11,10 +11,18 @@
           <Style.Animations>
             <Animation Duration="0:0:1" IterationCount="Infinite">
               <KeyFrame Cue="0%">
-                <Setter Property="Text" Value="" Animation.Animator="{x:Type pages:CustomStringAnimator}"/>
+                <Setter Property="Text" Value="">
+                  <Animation.Animator>
+                    <pages:CustomStringAnimator/>
+                  </Animation.Animator>
+                </Setter>
               </KeyFrame>
               <KeyFrame Cue="100%">
-                <Setter Property="Text" Value="0123456789" Animation.Animator="{x:Type pages:CustomStringAnimator}"/>
+                <Setter Property="Text" Value="0123456789" >
+                  <Animation.Animator>
+                    <pages:CustomStringAnimator/>
+                  </Animation.Animator>
+                </Setter>
               </KeyFrame>
             </Animation>
           </Style.Animations>

samples/RenderDemo/Pages/CustomStringAnimator.cs

@@ -1,8 +1,9 @@
-using Avalonia.Animation.Animators;
+using Avalonia.Animation;
+using Avalonia.Animation.Animators;
 
 namespace RenderDemo.Pages
 {
-    public class CustomStringAnimator : Animator<string>
+    public class CustomStringAnimator : CustomAnimatorBase<string>
     {
         public override string Interpolate(double progress, string oldValue, string newValue)
         {

samples/RenderDemo/Pages/Transform3DPage.axaml

@@ -134,9 +134,6 @@
     </UserControl.Styles>
 
     <Grid ColumnDefinitions="Auto,*,Auto,*" RowDefinitions="*, Auto, Auto, Auto, Auto, Auto, Auto, Auto">
-        <Grid.Clock>
-            <Clock />
-        </Grid.Clock>
         <Border Name="B1" Background="DarkRed" Classes="Test">
             <Border.RenderTransform>
                 <Rotate3DTransform CenterZ="-100"

samples/RenderDemo/Pages/TransitionsPage.xaml

@@ -248,12 +248,8 @@
 
   <Grid>
     <StackPanel HorizontalAlignment="Center" VerticalAlignment="Center" ClipToBounds="False">
-      <StackPanel.Clock>
-        <Clock />
-      </StackPanel.Clock>
       <StackPanel Orientation="Horizontal" VerticalAlignment="Center" Spacing="20">
         <TextBlock VerticalAlignment="Center">Hover to activate Transitions.</TextBlock>
-        <Button Content="{Binding PlayStateText}" Command="{Binding TogglePlayState}" Click="ToggleClock" />
       </StackPanel>
       <WrapPanel ClipToBounds="False">
         <Border Classes="Test Rect1" Background="DarkRed"/>

samples/RenderDemo/Pages/TransitionsPage.xaml.cs

@@ -18,20 +18,5 @@ namespace RenderDemo.Pages
         {
             AvaloniaXamlLoader.Load(this);
         }
-
-        private void ToggleClock(object sender, RoutedEventArgs args)
-        {
-            var button = sender as Button;
-            var clock = button.Clock;
-
-            if (clock.PlayState == PlayState.Run)
-            {
-                clock.PlayState = PlayState.Pause;
-            }
-            else if (clock.PlayState == PlayState.Pause)
-            {
-                clock.PlayState = PlayState.Run;
-            }
-        }
     }
 }

src/Android/Avalonia.Android/AndroidPlatform.cs

@@ -45,7 +45,6 @@ namespace Avalonia.Android
                 .Bind<IPlatformThreadingInterface>().ToConstant(new AndroidThreadingInterface())
                 .Bind<IPlatformIconLoader>().ToSingleton<PlatformIconLoaderStub>()
                 .Bind<IRenderTimer>().ToConstant(new ChoreographerTimer())
-                .Bind<IRenderLoop>().ToConstant(new RenderLoop())
                 .Bind<PlatformHotkeyConfiguration>().ToSingleton<PlatformHotkeyConfiguration>();
 
             if (Options.UseGpu)

src/Android/Avalonia.Android/Platform/SkiaPlatform/TopLevelImpl.cs

@@ -103,9 +103,8 @@ namespace Avalonia.Android.Platform.SkiaPlatform
 
         public IEnumerable<object> Surfaces => new object[] { _gl, _framebuffer, Handle };
 
-        public IRenderer CreateRenderer(IRenderRoot root) =>
-            new CompositingRenderer(root, AndroidPlatform.Compositor, () => Surfaces);
-
+        public Compositor Compositor => AndroidPlatform.Compositor;
+        
         public virtual void Hide()
         {
             _view.Visibility = ViewStates.Invisible;

src/Avalonia.Base/Animation/Animatable.cs

@@ -17,7 +17,7 @@ namespace Avalonia.Animation
         /// <summary>
         /// Defines the <see cref="Clock"/> property.
         /// </summary>
-        public static readonly StyledProperty<IClock> ClockProperty =
+        internal static readonly StyledProperty<IClock> ClockProperty =
             AvaloniaProperty.Register<Animatable, IClock>(nameof(Clock), inherits: true);
 
         /// <summary>
@@ -36,7 +36,7 @@ namespace Avalonia.Animation
         /// <summary>
         /// Gets or sets the clock which controls the animations on the control.
         /// </summary>
-        public IClock Clock
+        internal IClock Clock
         {
             get => GetValue(ClockProperty);
             set => SetValue(ClockProperty, value);

src/Avalonia.Base/Animation/Animation.cs

@@ -16,7 +16,7 @@ namespace Avalonia.Animation
     /// <summary>
     /// Tracks the progress of an animation.
     /// </summary>
-    public class Animation : AvaloniaObject, IAnimation
+    public sealed class Animation : AvaloniaObject, IAnimation
     {
         /// <summary>
         /// Defines the <see cref="Duration"/> property.
@@ -186,7 +186,7 @@ namespace Avalonia.Animation
         /// </summary>
         /// <param name="setter">The animation setter.</param>
         /// <returns>The property animator type.</returns>
-        public static (Type Type, Func<IAnimator> Factory)? GetAnimator(IAnimationSetter setter)
+        internal static (Type Type, Func<IAnimator> Factory)? GetAnimator(IAnimationSetter setter)
         {
             if (s_animators.TryGetValue(setter, out var type))
             {
@@ -200,11 +200,9 @@ namespace Avalonia.Animation
         /// </summary>
         /// <param name="setter">The animation setter.</param>
         /// <param name="value">The property animator value.</param>
-        public static void SetAnimator(IAnimationSetter setter,
-            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor | DynamicallyAccessedMemberTypes.PublicMethods)]
-            Type value)
+        public static void SetAnimator(IAnimationSetter setter, CustomAnimatorBase value)
         {
-            s_animators[setter] = (value, () => (IAnimator)Activator.CreateInstance(value)!);
+            s_animators[setter] = (value.WrapperType, value.CreateWrapper);
         }
 
         private readonly static List<(Func<AvaloniaProperty, bool> Condition, Type Animator, Func<IAnimator> Factory)> Animators = new()
@@ -233,7 +231,7 @@ namespace Avalonia.Animation
         /// <typeparam name="TAnimator">
         /// The type of the animator to instantiate.
         /// </typeparam>
-        public static void RegisterAnimator<TAnimator>(Func<AvaloniaProperty, bool> condition)
+        internal static void RegisterAnimator<TAnimator>(Func<AvaloniaProperty, bool> condition)
             where TAnimator : IAnimator, new()
         {
             Animators.Insert(0, (condition, typeof(TAnimator), () => new TAnimator()));
@@ -312,8 +310,11 @@ namespace Avalonia.Animation
             return (newAnimatorInstances, subscriptions);
         }
 
+        IDisposable IAnimation.Apply(Animatable control, IClock? clock, IObservable<bool> match, Action? onComplete)
+            => Apply(control, clock, match, onComplete);
+        
         /// <inheritdoc/>
-        public IDisposable Apply(Animatable control, IClock? clock, IObservable<bool> match, Action? onComplete)
+        internal IDisposable Apply(Animatable control, IClock? clock, IObservable<bool> match, Action? onComplete)
         {
             var (animators, subscriptions) = InterpretKeyframes(control);
             if (animators.Count == 1)
@@ -358,14 +359,19 @@ namespace Avalonia.Animation
             return new CompositeDisposable(subscriptions);
         }
 
+        public Task RunAsync(Animatable control) => RunAsync(control, null);
+        
         /// <inheritdoc/>
-        public Task RunAsync(Animatable control, IClock? clock = null)
+        internal Task RunAsync(Animatable control, IClock? clock)
         {
             return RunAsync(control, clock, default);
         }
 
+        Task IAnimation.RunAsync(Animatable control, IClock? clock, CancellationToken cancellationToken)
+            => RunAsync(control, clock, cancellationToken);
+        
         /// <inheritdoc/>
-        public Task RunAsync(Animatable control, IClock? clock = null, CancellationToken cancellationToken = default)
+        internal Task RunAsync(Animatable control, IClock? clock, CancellationToken cancellationToken)
         {
             if (cancellationToken.IsCancellationRequested)
             {

src/Avalonia.Base/Animation/AnimatorDrivenTransition.cs

@@ -1,5 +1,6 @@
 using System;
 using Avalonia.Animation.Animators;
+using Avalonia.Animation.Easings;
 
 namespace Avalonia.Animation
 {
@@ -8,13 +9,11 @@ namespace Avalonia.Animation
     /// </summary>
     /// <typeparam name="T">Type of the transitioned value.</typeparam>
     /// <typeparam name="TAnimator">Type of the animator.</typeparam>
-    public abstract class AnimatorDrivenTransition<T, TAnimator> : Transition<T> where TAnimator : Animator<T>, new()
+    internal static class AnimatorDrivenTransition<T, TAnimator> where TAnimator : Animator<T>, new()
     {
         private static readonly TAnimator s_animator = new TAnimator();
 
-        public override IObservable<T> DoTransition(IObservable<double> progress, T oldValue, T newValue)
-        {
-            return new AnimatorTransitionObservable<T, TAnimator>(s_animator, progress, Easing, oldValue, newValue);
-        }
+        public static IObservable<T> Transition(IEasing easing, IObservable<double> progress, T oldValue, T newValue) =>
+            new AnimatorTransitionObservable<T, TAnimator>(s_animator, progress, easing, oldValue, newValue);
     }
 }

src/Avalonia.Base/Animation/AnimatorKeyFrame.cs

@@ -11,7 +11,7 @@ namespace Avalonia.Animation
     /// Defines a KeyFrame that is used for
     /// <see cref="Animator{T}"/> objects.
     /// </summary>
-    public class AnimatorKeyFrame : AvaloniaObject
+    internal class AnimatorKeyFrame : AvaloniaObject
     {
         public static readonly DirectProperty<AnimatorKeyFrame, object?> ValueProperty =
             AvaloniaProperty.RegisterDirect<AnimatorKeyFrame, object?>(nameof(Value), k => k.Value, (k, v) => k.Value = v);

src/Avalonia.Base/Animation/AnimatorTransitionObservable.cs

@@ -9,17 +9,15 @@ namespace Avalonia.Animation
     /// </summary>
     /// <typeparam name="T">Type of the transitioned value.</typeparam>
     /// <typeparam name="TAnimator">Type of the animator.</typeparam>
-    public class AnimatorTransitionObservable<T, TAnimator> : TransitionObservableBase<T> where TAnimator : Animator<T>
+    internal class AnimatorTransitionObservable<T, TAnimator> : TransitionObservableBase<T> where TAnimator : Animator<T>
     {
         private readonly TAnimator _animator;
-        private readonly Easing _easing;
         private readonly T _oldValue;
         private readonly T _newValue;
 
-        public AnimatorTransitionObservable(TAnimator animator, IObservable<double> progress, Easing easing, T oldValue, T newValue) : base(progress, easing)
+        public AnimatorTransitionObservable(TAnimator animator, IObservable<double> progress, IEasing easing, T oldValue, T newValue) : base(progress, easing)
         {
             _animator = animator;
-            _easing = easing;
             _oldValue = oldValue;
             _newValue = newValue;
         }

src/Avalonia.Base/Animation/Animators/Animator`1.cs

@@ -11,7 +11,7 @@ namespace Avalonia.Animation.Animators
     /// <summary>
     /// Base class for <see cref="Animator{T}"/> objects
     /// </summary>
-    public abstract class Animator<T> : AvaloniaList<AnimatorKeyFrame>, IAnimator
+    internal abstract class Animator<T> : AvaloniaList<AnimatorKeyFrame>, IAnimator
     {
         /// <summary>
         /// List of type-converted keyframes.

src/Avalonia.Base/Animation/Animators/BaseBrushAnimator.cs

@@ -15,7 +15,7 @@ namespace Avalonia.Animation.Animators
     /// redirect them to the properly registered
     /// animators in this class.
     /// </summary>
-    public class BaseBrushAnimator : Animator<IBrush?>
+    internal class BaseBrushAnimator : Animator<IBrush?>
     {
         private static readonly List<(Func<Type, bool> Match, Type AnimatorType, Func<IAnimator> AnimatorFactory)> _brushAnimators = new();
 

src/Avalonia.Base/Animation/Animators/BoolAnimator.cs

@@ -3,7 +3,7 @@
     /// <summary>
     /// Animator that handles <see cref="bool"/> properties.
     /// </summary>
-    public class BoolAnimator : Animator<bool>
+    internal class BoolAnimator : Animator<bool>
     {
         /// <inheritdocs/>
         public override bool Interpolate(double progress, bool oldValue, bool newValue)

src/Avalonia.Base/Animation/Animators/BoxShadowAnimator.cs

@@ -2,7 +2,7 @@ using Avalonia.Media;
 
 namespace Avalonia.Animation.Animators
 {
-    public class BoxShadowAnimator : Animator<BoxShadow>
+    internal class BoxShadowAnimator : Animator<BoxShadow>
     {
         static ColorAnimator s_colorAnimator = new ColorAnimator();
         static DoubleAnimator s_doubleAnimator = new DoubleAnimator();

src/Avalonia.Base/Animation/Animators/BoxShadowsAnimator.cs

@@ -2,7 +2,7 @@ using Avalonia.Media;
 
 namespace Avalonia.Animation.Animators
 {
-    public class BoxShadowsAnimator :  Animator<BoxShadows>
+    internal class BoxShadowsAnimator : Animator<BoxShadows>
     {
         private static readonly BoxShadowAnimator s_boxShadowAnimator = new BoxShadowAnimator();
         public override BoxShadows Interpolate(double progress, BoxShadows oldValue, BoxShadows newValue)

src/Avalonia.Base/Animation/Animators/ByteAnimator.cs

@@ -5,7 +5,7 @@ namespace Avalonia.Animation.Animators
     /// <summary>
     /// Animator that handles <see cref="byte"/> properties.
     /// </summary>
-    public class ByteAnimator : Animator<byte>
+    internal class ByteAnimator : Animator<byte>
     {
         const double maxVal = (double)byte.MaxValue;
 

src/Avalonia.Base/Animation/Animators/ColorAnimator.cs

@@ -12,7 +12,7 @@ namespace Avalonia.Animation.Animators
     /// Animator that interpolates <see cref="Color"/> through 
     /// gamma sRGB color space for better visual result.
     /// </summary>
-    public class ColorAnimator : Animator<Color>
+    internal class ColorAnimator : Animator<Color>
     {
         /// <summary>
         /// Opto-electronic conversion function for the sRGB color space.

src/Avalonia.Base/Animation/Animators/CornerRadiusAnimator.cs

@@ -7,7 +7,7 @@ namespace Avalonia.Animation.Animators
     /// <summary>
     /// Animator that handles <see cref="CornerRadius"/> properties.
     /// </summary>
-    public class CornerRadiusAnimator : Animator<CornerRadius>
+    internal class CornerRadiusAnimator : Animator<CornerRadius>
     {
         public override CornerRadius Interpolate(double progress, CornerRadius oldValue, CornerRadius newValue)
         {

src/Avalonia.Base/Animation/Animators/DecimalAnimator.cs

@@ -3,7 +3,7 @@
     /// <summary>
     /// Animator that handles <see cref="decimal"/> properties.
     /// </summary>
-    public class DecimalAnimator : Animator<decimal>
+    internal class DecimalAnimator : Animator<decimal>
     {
         /// <inheritdocs/>
         public override decimal Interpolate(double progress, decimal oldValue, decimal newValue)

src/Avalonia.Base/Animation/Animators/DoubleAnimator.cs

@@ -3,7 +3,7 @@
     /// <summary>
     /// Animator that handles <see cref="double"/> properties.
     /// </summary>
-    public class DoubleAnimator : Animator<double>
+    internal class DoubleAnimator : Animator<double>
     {
         /// <inheritdocs/>
         public override double Interpolate(double progress, double oldValue, double newValue)

src/Avalonia.Base/Animation/Animators/FloatAnimator.cs

@@ -3,7 +3,7 @@
     /// <summary>
     /// Animator that handles <see cref="float"/> properties.
     /// </summary>
-    public class FloatAnimator : Animator<float>
+    internal class FloatAnimator : Animator<float>
     {
         /// <inheritdocs/>
         public override float Interpolate(double progress, float oldValue, float newValue)

src/Avalonia.Base/Animation/Animators/GradientBrushAnimator.cs

@@ -13,7 +13,7 @@ namespace Avalonia.Animation.Animators
     /// <summary>
     /// Animator that handles <see cref="SolidColorBrush"/> values. 
     /// </summary>
-    public class GradientBrushAnimator : Animator<IGradientBrush?>
+    internal class GradientBrushAnimator : Animator<IGradientBrush?>
     {
         private static readonly RelativePointAnimator s_relativePointAnimator = new RelativePointAnimator();
         private static readonly DoubleAnimator s_doubleAnimator = new DoubleAnimator();

src/Avalonia.Base/Animation/Animators/Int16Animator.cs

@@ -5,7 +5,7 @@ namespace Avalonia.Animation.Animators
     /// <summary>
     /// Animator that handles <see cref="Int16"/> properties.
     /// </summary>
-    public class Int16Animator : Animator<Int16>
+    internal class Int16Animator : Animator<Int16>
     {
         const double maxVal = (double)Int16.MaxValue;
 

src/Avalonia.Base/Animation/Animators/Int32Animator.cs

@@ -5,7 +5,7 @@ namespace Avalonia.Animation.Animators
     /// <summary>
     /// Animator that handles <see cref="Int32"/> properties.
     /// </summary>
-    public class Int32Animator : Animator<Int32>
+    internal class Int32Animator : Animator<Int32>
     {
         const double maxVal = (double)Int32.MaxValue;
 

src/Avalonia.Base/Animation/Animators/Int64Animator.cs

@@ -5,7 +5,7 @@ namespace Avalonia.Animation.Animators
     /// <summary>
     /// Animator that handles <see cref="Int64"/> properties.
     /// </summary>
-    public class Int64Animator : Animator<Int64>
+    internal class Int64Animator : Animator<Int64>
     {
         const double maxVal = (double)Int64.MaxValue;
 

src/Avalonia.Base/Animation/Animators/PointAnimator.cs

@@ -7,7 +7,7 @@ namespace Avalonia.Animation.Animators
     /// <summary>
     /// Animator that handles <see cref="Point"/> properties.
     /// </summary>
-    public class PointAnimator : Animator<Point>
+    internal class PointAnimator : Animator<Point>
     {
         public override Point Interpolate(double progress, Point oldValue, Point newValue)
         { 

src/Avalonia.Base/Animation/Animators/RectAnimator.cs

@@ -7,7 +7,7 @@ namespace Avalonia.Animation.Animators
     /// <summary>
     /// Animator that handles <see cref="Rect"/> properties.
     /// </summary>
-    public class RectAnimator : Animator<Rect>
+    internal class RectAnimator : Animator<Rect>
     {
         public override Rect Interpolate(double progress, Rect oldValue, Rect newValue)
         {

src/Avalonia.Base/Animation/Animators/RelativePointAnimator.cs

@@ -3,7 +3,7 @@
     /// <summary>
     /// Animator that handles <see cref="RelativePoint"/> properties.
     /// </summary>
-    public class RelativePointAnimator : Animator<RelativePoint>
+    internal class RelativePointAnimator : Animator<RelativePoint>
     {
         private static readonly PointAnimator s_pointAnimator = new PointAnimator();
 

src/Avalonia.Base/Animation/Animators/SizeAnimator.cs

@@ -7,7 +7,7 @@ namespace Avalonia.Animation.Animators
     /// <summary>
     /// Animator that handles <see cref="Size"/> properties.
     /// </summary>
-    public class SizeAnimator : Animator<Size>
+    internal class SizeAnimator : Animator<Size>
     {
         public override Size Interpolate(double progress, Size oldValue, Size newValue)
         {

src/Avalonia.Base/Animation/Animators/SolidColorBrushAnimator.cs

@@ -10,7 +10,7 @@ namespace Avalonia.Animation.Animators
     /// <summary>
     /// Animator that handles <see cref="SolidColorBrush"/> values. 
     /// </summary>
-    public class ISolidColorBrushAnimator : Animator<ISolidColorBrush?>
+    internal class ISolidColorBrushAnimator : Animator<ISolidColorBrush?>
     {
         private static readonly DoubleAnimator s_doubleAnimator = new DoubleAnimator();
 

src/Avalonia.Base/Animation/Animators/ThicknessAnimator.cs

@@ -7,7 +7,7 @@ namespace Avalonia.Animation.Animators
     /// <summary>
     /// Animator that handles <see cref="Thickness"/> properties.
     /// </summary>
-    public class ThicknessAnimator : Animator<Thickness>
+    internal class ThicknessAnimator : Animator<Thickness>
     {
         public override Thickness Interpolate(double progress, Thickness oldValue, Thickness newValue)
         {

src/Avalonia.Base/Animation/Animators/TransformAnimator.cs

@@ -9,7 +9,7 @@ namespace Avalonia.Animation.Animators
     /// <summary>
     /// Animator that handles <see cref="Transform"/> properties.
     /// </summary>
-    public class TransformAnimator : Animator<double>
+    internal class TransformAnimator : Animator<double>
     {
         DoubleAnimator? _doubleAnimator;
 

src/Avalonia.Base/Animation/Animators/TransformOperationsAnimator.cs

@@ -4,7 +4,7 @@ using Avalonia.Media.Transformation;
 
 namespace Avalonia.Animation.Animators
 {
-    public class TransformOperationsAnimator : Animator<TransformOperations>
+    internal class TransformOperationsAnimator : Animator<TransformOperations>
     {
         public TransformOperationsAnimator()
         {

src/Avalonia.Base/Animation/Animators/UInt16Animator.cs

@@ -5,7 +5,7 @@ namespace Avalonia.Animation.Animators
     /// <summary>
     /// Animator that handles <see cref="UInt16"/> properties.
     /// </summary>
-    public class UInt16Animator : Animator<UInt16>
+    internal class UInt16Animator : Animator<UInt16>
     {
         const double maxVal = (double)UInt16.MaxValue;
 

src/Avalonia.Base/Animation/Animators/UInt32Animator.cs

@@ -5,7 +5,7 @@ namespace Avalonia.Animation.Animators
     /// <summary>
     /// Animator that handles <see cref="UInt32"/> properties.
     /// </summary>
-    public class UInt32Animator : Animator<UInt32>
+    internal class UInt32Animator : Animator<UInt32>
     {
         const double maxVal = (double)UInt32.MaxValue;
 

src/Avalonia.Base/Animation/Animators/UInt64Animator.cs

@@ -5,7 +5,7 @@ namespace Avalonia.Animation.Animators
     /// <summary>
     /// Animator that handles <see cref="UInt64"/> properties.
     /// </summary>
-    public class UInt64Animator : Animator<UInt64>
+    internal class UInt64Animator : Animator<UInt64>
     {
         const double maxVal = (double)UInt64.MaxValue;
 

src/Avalonia.Base/Animation/Animators/VectorAnimator.cs

@@ -7,7 +7,7 @@ namespace Avalonia.Animation.Animators
     /// <summary>
     /// Animator that handles <see cref="Vector"/> properties.
     /// </summary>
-    public class VectorAnimator : Animator<Vector>
+    internal class VectorAnimator : Animator<Vector>
     {
         public override Vector Interpolate(double progress, Vector oldValue, Vector newValue)
         {

src/Avalonia.Base/Animation/Clock.cs

@@ -3,7 +3,10 @@ using Avalonia.Reactive;
 
 namespace Avalonia.Animation
 {
-    public class Clock : ClockBase
+    // Note: this class was always broken: it subscribes to the global clock immediately even it if
+    // doesn't actually have subscriptions
+    
+    internal class Clock : ClockBase
     {
         public static IClock GlobalClock => AvaloniaLocator.Current.GetRequiredService<IGlobalClock>();
 

src/Avalonia.Base/Animation/ClockBase.cs

@@ -3,7 +3,7 @@ using Avalonia.Reactive;
 
 namespace Avalonia.Animation
 {
-    public class ClockBase : IClock
+    internal class ClockBase : IClock
     {
         private readonly ClockObservable _observable;
 

src/Avalonia.Base/Animation/Easings/SpringEasing.cs

@@ -64,11 +64,6 @@ public class SpringEasing : Easing
         Damping = damping;
         InitialVelocity = initialVelocity;
     }
-
-    public SpringEasing(Spring keySpline)
-    {
-        _internalSpring = keySpline;
-    }
     
     public SpringEasing()
     {

src/Avalonia.Base/Animation/IAnimation.cs

@@ -14,11 +14,11 @@ namespace Avalonia.Animation
         /// <summary>
         /// Apply the animation to the specified control and run it when <paramref name="match" /> produces <c>true</c>.
         /// </summary>
-        IDisposable Apply(Animatable control, IClock? clock, IObservable<bool> match, Action? onComplete = null);
+        internal IDisposable Apply(Animatable control, IClock? clock, IObservable<bool> match, Action? onComplete = null);
 
         /// <summary>
         /// Run the animation on the specified control.
         /// </summary>
-        Task RunAsync(Animatable control, IClock clock, CancellationToken cancellationToken = default);
+        internal Task RunAsync(Animatable control, IClock clock, CancellationToken cancellationToken = default);
     }
 }

src/Avalonia.Base/Animation/IAnimationSetter.cs

@@ -2,7 +2,7 @@ using Avalonia.Metadata;
 
 namespace Avalonia.Animation
 {
-    [NotClientImplementable]
+    [NotClientImplementable, PrivateApi]
     public interface IAnimationSetter
     {
         AvaloniaProperty? Property { get; set; }

src/Avalonia.Base/Animation/IAnimator.cs

@@ -7,8 +7,7 @@ namespace Avalonia.Animation
     /// <summary>
     /// Interface for Animator objects
     /// </summary>
-    [NotClientImplementable]
-    public interface IAnimator : IList<AnimatorKeyFrame>
+    internal interface IAnimator : IList<AnimatorKeyFrame>
     {
         /// <summary>
         /// The target property.

src/Avalonia.Base/Animation/IClock.cs

@@ -3,8 +3,7 @@ using Avalonia.Metadata;
 
 namespace Avalonia.Animation
 {
-    [NotClientImplementable]
-    public interface IClock : IObservable<TimeSpan>
+    internal interface IClock : IObservable<TimeSpan>
     {
         PlayState PlayState { get; set; }
     }

src/Avalonia.Base/Animation/ICustomAnimator.cs

@@ -0,0 +1,30 @@
+using System;
+using Avalonia.Animation.Animators;
+
+namespace Avalonia.Animation;
+
+public abstract class CustomAnimatorBase
+{
+    internal abstract IAnimator CreateWrapper();
+    internal abstract Type WrapperType { get; }
+}
+
+public abstract class CustomAnimatorBase<T> : CustomAnimatorBase
+{
+    public abstract T Interpolate(double progress, T oldValue, T newValue);
+
+    internal override Type WrapperType => typeof(AnimatorWrapper);
+    internal override IAnimator CreateWrapper() => new AnimatorWrapper(this);
+
+    internal class AnimatorWrapper : Animator<T>
+    {
+        private readonly CustomAnimatorBase<T> _parent;
+
+        public AnimatorWrapper(CustomAnimatorBase<T> parent)
+        {
+            _parent = parent;
+        }
+        
+        public override T Interpolate(double progress, T oldValue, T newValue) => _parent.Interpolate(progress, oldValue, newValue);
+    }
+}

src/Avalonia.Base/Animation/IGlobalClock.cs

@@ -2,8 +2,7 @@ using Avalonia.Metadata;
 
 namespace Avalonia.Animation
 {
-    [NotClientImplementable]
-    public interface IGlobalClock : IClock
+    internal interface IGlobalClock : IClock
     {
     }
 }

src/Avalonia.Base/Animation/ITransition.cs

@@ -6,13 +6,13 @@ namespace Avalonia.Animation
     /// <summary>
     /// Interface for Transition objects.
     /// </summary>
-    [NotClientImplementable]
+    [NotClientImplementable, PrivateApi]
     public interface ITransition
     {
         /// <summary>
         /// Applies the transition to the specified <see cref="Animatable"/>.
         /// </summary>
-        IDisposable Apply(Animatable control, IClock clock, object? oldValue, object? newValue);
+        internal IDisposable Apply(Animatable control, IClock clock, object? oldValue, object? newValue);
 
         /// <summary>
         /// Gets the property to be animated.

src/Avalonia.Base/Animation/KeyFrame.cs

@@ -15,7 +15,7 @@ namespace Avalonia.Animation
     /// Stores data regarding a specific key
     /// point and value in an animation.
     /// </summary>
-    public class KeyFrame : AvaloniaObject
+    public sealed class KeyFrame : AvaloniaObject
     {
         private TimeSpan _ktimeSpan;
         private Cue _kCue;

src/Avalonia.Base/Animation/KeyFrames.cs

@@ -7,7 +7,7 @@ namespace Avalonia.Animation
     /// <summary>
     /// A collection of <see cref="KeyFrame"/>s.
     /// </summary>
-    public class KeyFrames : AvaloniaList<KeyFrame>
+    public sealed class KeyFrames : AvaloniaList<KeyFrame>
     {
         /// <summary>
         /// Initializes a new instance of the <see cref="KeyFrames"/> class.

src/Avalonia.Base/Animation/KeySpline.cs

@@ -17,7 +17,7 @@ namespace Avalonia.Animation
     /// See https://docs.microsoft.com/en-us/dotnet/api/system.windows.media.animation.keyspline
     /// </summary>
     [TypeConverter(typeof(KeySplineTypeConverter))]
-    public class KeySpline : AvaloniaObject
+    public sealed class KeySpline : AvaloniaObject
     {
         // Control points
         private double _controlPointX1;

src/Avalonia.Base/Animation/RenderLoopClock.cs

@@ -1,26 +0,0 @@
-using System;
-using System.Collections.Generic;
-using System.Text;
-using Avalonia.Rendering;
-
-namespace Avalonia.Animation
-{
-    public class RenderLoopClock : ClockBase, IRenderLoopTask, IGlobalClock
-    {
-        protected override void Stop()
-        {
-            AvaloniaLocator.Current.GetRequiredService<IRenderLoop>().Remove(this);
-        }
-
-        bool IRenderLoopTask.NeedsUpdate => HasSubscriptions;
-
-        void IRenderLoopTask.Render()
-        {
-        }
-
-        void IRenderLoopTask.Update(TimeSpan time)
-        {
-            Pulse(time);
-        }
-    }
-}

src/Avalonia.Base/Animation/Spring.cs

@@ -10,7 +10,7 @@ namespace Avalonia.Animation;
 /// Determines how an animation is used based on spring formula.
 /// </summary>
 [TypeConverter(typeof(SpringTypeConverter))]
-public class Spring
+internal class Spring
 {
     private SpringSolver _springSolver;
     private double _mass;

src/Avalonia.Base/Animation/SpringTypeConverter.cs

@@ -7,7 +7,7 @@ namespace Avalonia.Animation;
 /// <summary>
 /// Converts string values to <see cref="Spring"/> values.
 /// </summary>
-public class SpringTypeConverter : TypeConverter
+internal class SpringTypeConverter : TypeConverter
 {
     public override bool CanConvertFrom(ITypeDescriptorContext? context, Type sourceType)
     {

src/Avalonia.Base/Animation/Transition.cs

@@ -53,10 +53,13 @@ namespace Avalonia.Animation
         /// <summary>
         /// Apply interpolation to the property.
         /// </summary>
-        public abstract IObservable<T> DoTransition(IObservable<double> progress, T oldValue, T newValue);
+        internal abstract IObservable<T> DoTransition(IObservable<double> progress, T oldValue, T newValue);
 
         /// <inheritdocs/>
-        public virtual IDisposable Apply(Animatable control, IClock clock, object? oldValue, object? newValue)
+        IDisposable ITransition.Apply(Animatable control, IClock clock, object? oldValue, object? newValue)
+            => Apply(control, clock, oldValue, newValue);
+        
+        internal virtual IDisposable Apply(Animatable control, IClock clock, object? oldValue, object? newValue)
         {
             if (Property is null)
                 throw new InvalidOperationException("Transition has no property specified.");

src/Avalonia.Base/Animation/TransitionObservableBase.cs

@@ -12,11 +12,11 @@ namespace Avalonia.Animation
     /// <typeparam name="T">Type of the transitioned value.</typeparam>
     public abstract class TransitionObservableBase<T> : SingleSubscriberObservableBase<T>, IObserver<double>
     {
-        private readonly Easing _easing;
+        private readonly IEasing _easing;
         private readonly IObservable<double> _progress;
         private IDisposable? _progressSubscription;
 
-        protected TransitionObservableBase(IObservable<double> progress, Easing easing)
+        protected TransitionObservableBase(IObservable<double> progress, IEasing easing)
         {
             _progress = progress;
             _easing = easing;

src/Avalonia.Base/Animation/Transitions.cs

@@ -7,7 +7,7 @@ namespace Avalonia.Animation
     /// <summary>
     /// A collection of <see cref="ITransition"/> definitions.
     /// </summary>
-    public class Transitions : AvaloniaList<ITransition>
+    public sealed class Transitions : AvaloniaList<ITransition>
     {
         /// <summary>
         /// Initializes a new instance of the <see cref="Transitions"/> class.

src/Avalonia.Base/Animation/Transitions/BoxShadowsTransition.cs

@@ -1,3 +1,4 @@
+using System;
 using Avalonia.Animation.Animators;
 using Avalonia.Media;
 
@@ -6,7 +7,10 @@ namespace Avalonia.Animation
     /// <summary>
     /// Transition class that handles <see cref="AvaloniaProperty"/> with <see cref="BoxShadows"/> type.
     /// </summary>  
-    public class BoxShadowsTransition : AnimatorDrivenTransition<BoxShadows, BoxShadowsAnimator>
+    public class BoxShadowsTransition : Transition<BoxShadows>
     {
+        internal override IObservable<BoxShadows> DoTransition(IObservable<double> progress, BoxShadows oldValue,
+            BoxShadows newValue) =>
+            AnimatorDrivenTransition<BoxShadows, BoxShadowsAnimator>.Transition(Easing, progress, oldValue, newValue);
     }
 }

src/Avalonia.Base/Animation/Transitions/BrushTransition.cs

@@ -16,7 +16,7 @@ namespace Avalonia.Animation
         private static readonly GradientBrushAnimator s_gradientAnimator = new GradientBrushAnimator();
         private static readonly ISolidColorBrushAnimator s_solidColorBrushAnimator = new ISolidColorBrushAnimator();
 
-        public override IObservable<IBrush?> DoTransition(IObservable<double> progress, IBrush? oldValue, IBrush? newValue)
+        internal override IObservable<IBrush?> DoTransition(IObservable<double> progress, IBrush? oldValue, IBrush? newValue)
         {
             if (oldValue is null || newValue is null)
             {

src/Avalonia.Base/Animation/Transitions/ColorTransition.cs

@@ -1,4 +1,5 @@
-using Avalonia.Animation.Animators;
+using System;
+using Avalonia.Animation.Animators;
 using Avalonia.Media;
 
 namespace Avalonia.Animation
@@ -6,7 +7,9 @@ namespace Avalonia.Animation
     /// <summary>
     /// Transition class that handles <see cref="AvaloniaProperty"/> with <see cref="Color"/> type.
     /// </summary>
-    public class ColorTransition : AnimatorDrivenTransition<Color, ColorAnimator>
+    public class ColorTransition : Transition<Color>
     {
+        internal override IObservable<Color> DoTransition(IObservable<double> progress, Color oldValue, Color newValue)
+            => AnimatorDrivenTransition<Color, ColorAnimator>.Transition(Easing, progress, oldValue, newValue);
     }
 }

src/Avalonia.Base/Animation/Transitions/CornerRadiusTransition.cs

@@ -1,3 +1,4 @@
+using System;
 using Avalonia.Animation.Animators;
 
 namespace Avalonia.Animation
@@ -5,7 +6,11 @@ namespace Avalonia.Animation
     /// <summary>
     /// Transition class that handles <see cref="AvaloniaProperty"/> with <see cref="CornerRadius"/> type.
     /// </summary>  
-    public class CornerRadiusTransition : AnimatorDrivenTransition<CornerRadius, CornerRadiusAnimator>
+    public class CornerRadiusTransition : Transition<CornerRadius>
     {
+        internal override IObservable<CornerRadius> DoTransition(IObservable<double> progress, CornerRadius oldValue,
+            CornerRadius newValue) =>
+            AnimatorDrivenTransition<CornerRadius, CornerRadiusAnimator>.Transition(Easing, progress, oldValue,
+                newValue);
     }
 }

src/Avalonia.Base/Animation/Transitions/DoubleTransition.cs

@@ -1,3 +1,4 @@
+using System;
 using Avalonia.Animation.Animators;
 
 namespace Avalonia.Animation
@@ -5,7 +6,9 @@ namespace Avalonia.Animation
     /// <summary>
     /// Transition class that handles <see cref="AvaloniaProperty"/> with <see cref="double"/> types.
     /// </summary>  
-    public class DoubleTransition : AnimatorDrivenTransition<double, DoubleAnimator>
+    public class DoubleTransition : Transition<double>
     {
+        internal override IObservable<double> DoTransition(IObservable<double> progress, double oldValue, double newValue) => 
+            AnimatorDrivenTransition<double, DoubleAnimator>.Transition(Easing, progress, oldValue, newValue);
     }
 }

src/Avalonia.Base/Animation/Transitions/FloatTransition.cs

@@ -1,3 +1,4 @@
+using System;
 using Avalonia.Animation.Animators;
 
 namespace Avalonia.Animation
@@ -5,7 +6,9 @@ namespace Avalonia.Animation
     /// <summary>
     /// Transition class that handles <see cref="AvaloniaProperty"/> with <see cref="float"/> types.
     /// </summary>  
-    public class FloatTransition : AnimatorDrivenTransition<float, FloatAnimator>
+    public class FloatTransition : Transition<float>
     {
+        internal override IObservable<float> DoTransition(IObservable<double> progress, float oldValue, float newValue) => 
+            AnimatorDrivenTransition<float, FloatAnimator>.Transition(Easing, progress, oldValue, newValue);
     }
 }

src/Avalonia.Base/Animation/Transitions/IntegerTransition.cs

@@ -1,3 +1,4 @@
+using System;
 using Avalonia.Animation.Animators;
 
 namespace Avalonia.Animation
@@ -5,7 +6,9 @@ namespace Avalonia.Animation
     /// <summary>
     /// Transition class that handles <see cref="AvaloniaProperty"/> with <see cref="int"/> types.
     /// </summary>  
-    public class IntegerTransition : AnimatorDrivenTransition<int, Int32Animator>
+    public class IntegerTransition : Transition<int>
     {
+        internal override IObservable<int> DoTransition(IObservable<double> progress, int oldValue, int newValue) => 
+            AnimatorDrivenTransition<int, Int32Animator>.Transition(Easing, progress, oldValue, newValue);
     }
 }

src/Avalonia.Base/Animation/Transitions/PointTransition.cs

@@ -1,3 +1,4 @@
+using System;
 using Avalonia.Animation.Animators;
 
 namespace Avalonia.Animation
@@ -5,7 +6,9 @@ namespace Avalonia.Animation
     /// <summary>
     /// Transition class that handles <see cref="AvaloniaProperty"/> with <see cref="Point"/> type.
     /// </summary>  
-    public class PointTransition : AnimatorDrivenTransition<Point, PointAnimator>
+    public class PointTransition : Transition<Point>
     {
+        internal override IObservable<Point> DoTransition(IObservable<double> progress, Point oldValue, Point newValue) => 
+            AnimatorDrivenTransition<Point, PointAnimator>.Transition(Easing, progress, oldValue, newValue);
     }
 }

src/Avalonia.Base/Animation/Transitions/RelativePointTransition.cs

@@ -1,3 +1,4 @@
+using System;
 using Avalonia.Animation.Animators;
 
 namespace Avalonia.Animation
@@ -5,7 +6,9 @@ namespace Avalonia.Animation
     /// <summary>
     /// Transition class that handles <see cref="AvaloniaProperty"/> with <see cref="RelativePoint"/> type.
     /// </summary>  
-    public class RelativePointTransition : AnimatorDrivenTransition<RelativePoint, RelativePointAnimator>
+    public class RelativePointTransition : Transition<RelativePoint>
     {
+        internal override IObservable<RelativePoint> DoTransition(IObservable<double> progress, RelativePoint oldValue, RelativePoint newValue) =>
+            AnimatorDrivenTransition<RelativePoint, RelativePointAnimator>.Transition(Easing, progress, oldValue, newValue);
     }
 }

src/Avalonia.Base/Animation/Transitions/SizeTransition.cs

@@ -1,3 +1,4 @@
+using System;
 using Avalonia.Animation.Animators;
 
 namespace Avalonia.Animation
@@ -5,7 +6,9 @@ namespace Avalonia.Animation
     /// <summary>
     /// Transition class that handles <see cref="AvaloniaProperty"/> with <see cref="Size"/> type.
     /// </summary>  
-    public class SizeTransition : AnimatorDrivenTransition<Size, SizeAnimator>
+    public class SizeTransition : Transition<Size>
     {
+        internal override IObservable<Size> DoTransition(IObservable<double> progress, Size oldValue, Size newValue) => 
+            AnimatorDrivenTransition<Size, SizeAnimator>.Transition(Easing, progress, oldValue, newValue);
     }
 }

src/Avalonia.Base/Animation/Transitions/ThicknessTransition.cs

@@ -1,3 +1,4 @@
+using System;
 using Avalonia.Animation.Animators;
 
 namespace Avalonia.Animation
@@ -5,7 +6,9 @@ namespace Avalonia.Animation
     /// <summary>
     /// Transition class that handles <see cref="AvaloniaProperty"/> with <see cref="Thickness"/> type.
     /// </summary>  
-    public class ThicknessTransition : AnimatorDrivenTransition<Thickness, ThicknessAnimator>
+    public class ThicknessTransition : Transition<Thickness>
     {
+        internal override IObservable<Thickness> DoTransition(IObservable<double> progress, Thickness oldValue, Thickness newValue) => 
+            AnimatorDrivenTransition<Thickness, ThicknessAnimator>.Transition(Easing, progress, oldValue, newValue);
     }
 }

src/Avalonia.Base/Animation/Transitions/TransformOperationsTransition.cs

@@ -11,7 +11,7 @@ namespace Avalonia.Animation
     {
         private static readonly TransformOperationsAnimator s_operationsAnimator = new TransformOperationsAnimator();
 
-        public override IObservable<ITransform> DoTransition(
+        internal override IObservable<ITransform> DoTransition(
             IObservable<double> progress,
             ITransform oldValue,
             ITransform newValue)

src/Avalonia.Base/Animation/Transitions/VectorTransition.cs

@@ -1,3 +1,4 @@
+using System;
 using Avalonia.Animation.Animators;
 
 namespace Avalonia.Animation
@@ -5,7 +6,9 @@ namespace Avalonia.Animation
     /// <summary>
     /// Transition class that handles <see cref="AvaloniaProperty"/> with <see cref="Vector"/> type.
     /// </summary>  
-    public class VectorTransition : AnimatorDrivenTransition<Vector, VectorAnimator>
+    public class VectorTransition : Transition<Vector>
     {
+        internal override IObservable<Vector> DoTransition(IObservable<double> progress, Vector oldValue, Vector newValue) => 
+            AnimatorDrivenTransition<Vector, VectorAnimator>.Transition(Easing, progress, oldValue, newValue);
     }
 }

src/Avalonia.Base/Input/TextInput/TransformTrackingHelper.cs

@@ -91,7 +91,7 @@ namespace Avalonia.Input.TextInput
             if(_queuedForUpdate)
                 return;
             _queuedForUpdate = true;
-            Dispatcher.UIThread.Post(UpdateMatrix, DispatcherPriority.Render);
+            Dispatcher.UIThread.Post(UpdateMatrix, DispatcherPriority.AfterRender);
         }
 
         private void PropertyChangedHandler(object? sender, AvaloniaPropertyChangedEventArgs e)

src/Avalonia.Base/Layout/ILayoutManager.cs

@@ -7,7 +7,7 @@ namespace Avalonia.Layout
     /// Manages measuring and arranging of controls.
     /// </summary>
     [NotClientImplementable]
-    public interface ILayoutManager : IDisposable
+    internal interface ILayoutManager : IDisposable
     {
         /// <summary>
         /// Raised when the layout manager completes a layout pass.

src/Avalonia.Base/Layout/ILayoutRoot.cs

@@ -21,6 +21,6 @@ namespace Avalonia.Layout
         /// <summary>
         /// Associated instance of layout manager
         /// </summary>
-        ILayoutManager LayoutManager { get; }
+        internal ILayoutManager LayoutManager { get; }
     }
 }

src/Avalonia.Base/Layout/LayoutManager.cs

@@ -4,6 +4,7 @@ using System.Collections.Generic;
 using System.Diagnostics;
 using System.Linq;
 using Avalonia.Logging;
+using Avalonia.Media;
 using Avalonia.Rendering;
 using Avalonia.Threading;
 using Avalonia.Utilities;
@@ -15,14 +16,13 @@ namespace Avalonia.Layout
     /// <summary>
     /// Manages measuring and arranging of controls.
     /// </summary>
-    public class LayoutManager : ILayoutManager, IDisposable
+    internal class LayoutManager : ILayoutManager, IDisposable
     {
         private const int MaxPasses = 10;
         private readonly Layoutable _owner;
         private readonly LayoutQueue<Layoutable> _toMeasure = new LayoutQueue<Layoutable>(v => !v.IsMeasureValid);
         private readonly LayoutQueue<Layoutable> _toArrange = new LayoutQueue<Layoutable>(v => !v.IsArrangeValid);
         private readonly List<Layoutable> _toArrangeAfterMeasure = new();
-        private readonly Action _executeLayoutPass;
         private List<EffectiveViewportChangedListener>? _effectiveViewportChangedListeners;
         private bool _disposed;
         private bool _queued;
@@ -32,7 +32,6 @@ namespace Avalonia.Layout
         public LayoutManager(ILayoutRoot owner)
         {
             _owner = owner as Layoutable ?? throw new ArgumentNullException(nameof(owner));
-            _executeLayoutPass = ExecuteQueuedLayoutPass;
         }
 
         public virtual event EventHandler? LayoutUpdated;
@@ -99,7 +98,7 @@ namespace Avalonia.Layout
             QueueLayoutPass();
         }
 
-        private void ExecuteQueuedLayoutPass()
+        internal void ExecuteQueuedLayoutPass()
         {
             if (!_queued)
             {
@@ -346,7 +345,7 @@ namespace Avalonia.Layout
             if (!_queued && !_running)
             {
                 _queued = true;
-                Dispatcher.UIThread.Post(_executeLayoutPass, DispatcherPriority.Layout);
+                MediaContext.Instance.QueueLayoutPass(this);
             }
         }
 

src/Avalonia.Base/Media/DashStyle.cs

@@ -13,7 +13,7 @@ namespace Avalonia.Media
     /// <summary>
     /// Represents the sequence of dashes and gaps that will be applied by a <see cref="Pen"/>.
     /// </summary>
-    public class DashStyle : Animatable, IDashStyle
+    public sealed class DashStyle : Animatable, IDashStyle
     {
         /// <summary>
         /// Defines the <see cref="Dashes"/> property.

src/Avalonia.Base/Media/Drawing.cs

@@ -5,6 +5,11 @@
     /// </summary>
     public abstract class Drawing : AvaloniaObject
     {
+        internal Drawing()
+        {
+            
+        }
+        
         /// <summary>
         /// Draws this drawing to the given <see cref="DrawingContext"/>.
         /// </summary>

src/Avalonia.Base/Media/DrawingBrush.cs

@@ -12,7 +12,7 @@ namespace Avalonia.Media
     /// <summary>
     /// Paints an area with an <see cref="Drawing"/>.
     /// </summary>
-    public class DrawingBrush : TileBrush, ISceneBrush
+    public sealed class DrawingBrush : TileBrush, ISceneBrush
     {
         /// <summary>
         /// Defines the <see cref="Drawing"/> property.

src/Avalonia.Base/Media/DrawingGroup.cs

@@ -8,7 +8,7 @@ using Avalonia.Utilities;
 
 namespace Avalonia.Media
 {
-    public class DrawingGroup : Drawing
+    public sealed class DrawingGroup : Drawing
     {
         public static readonly StyledProperty<double> OpacityProperty =
             AvaloniaProperty.Register<DrawingGroup, double>(nameof(Opacity), 1);

src/Avalonia.Base/Media/Effects/BlurEffect.cs

@@ -2,7 +2,7 @@ using System;
 // ReSharper disable CheckNamespace
 namespace Avalonia.Media;
 
-public class BlurEffect : Effect, IBlurEffect, IMutableEffect
+public sealed class BlurEffect : Effect, IBlurEffect, IMutableEffect
 {
     public static readonly StyledProperty<double> RadiusProperty = AvaloniaProperty.Register<BlurEffect, double>(
         nameof(Radius), 5);

src/Avalonia.Base/Media/Effects/DropShadowEffect.cs

@@ -42,7 +42,7 @@ public abstract class DropShadowEffectBase : Effect
     }
 }
 
-public class DropShadowEffect : DropShadowEffectBase, IDropShadowEffect, IMutableEffect
+public sealed class DropShadowEffect : DropShadowEffectBase, IDropShadowEffect, IMutableEffect
 {
     public static readonly StyledProperty<double> OffsetXProperty = AvaloniaProperty.Register<DropShadowEffect, double>(
         nameof(OffsetX), 3.5355);
@@ -76,7 +76,7 @@ public class DropShadowEffect : DropShadowEffectBase, IDropShadowEffect, IMutabl
 /// <summary>
 /// This class is compatible with WPF's DropShadowEffect and provides Direction and ShadowDepth properties instead of OffsetX/OffsetY
 /// </summary>
-public class DropShadowDirectionEffect : DropShadowEffectBase, IDirectionDropShadowEffect, IMutableEffect
+public sealed class DropShadowDirectionEffect : DropShadowEffectBase, IDirectionDropShadowEffect, IMutableEffect
 {
     public static readonly StyledProperty<double> ShadowDepthProperty =
         AvaloniaProperty.Register<DropShadowDirectionEffect, double>(

src/Avalonia.Base/Media/Effects/Effect.cs

@@ -90,4 +90,9 @@ public class Effect : Animatable, IAffectsRender
     {
         EffectAnimator.EnsureRegistered();
     }
+
+    internal Effect()
+    {
+        
+    }
 }

src/Avalonia.Base/Media/Effects/EffectAnimator.cs

@@ -7,7 +7,7 @@ using Avalonia.Media;
 // ReSharper disable once CheckNamespace
 namespace Avalonia.Animation.Animators;
 
-public class EffectAnimator : Animator<IEffect?>
+internal class EffectAnimator : Animator<IEffect?>
 {
     public override IDisposable? Apply(Animation animation, Animatable control, IClock? clock,
         IObservable<bool> match, Action? onComplete)
@@ -68,7 +68,7 @@ public class EffectAnimator : Animator<IEffect?>
     }
 }
 
-public abstract class EffectAnimatorBase<T> : Animator<IEffect?> where T : class, IEffect?
+internal abstract class EffectAnimatorBase<T> : Animator<IEffect?> where T : class, IEffect?
 {
     public override IDisposable BindAnimation(Animatable control, IObservable<IEffect?> instance)
     {
@@ -91,7 +91,7 @@ public abstract class EffectAnimatorBase<T> : Animator<IEffect?> where T : class
     }
 }
 
-public class BlurEffectAnimator : EffectAnimatorBase<IBlurEffect>
+internal class BlurEffectAnimator : EffectAnimatorBase<IBlurEffect>
 {
     private static readonly DoubleAnimator s_doubleAnimator = new DoubleAnimator();
 
@@ -102,7 +102,7 @@ public class BlurEffectAnimator : EffectAnimatorBase<IBlurEffect>
     }
 }
 
-public class DropShadowEffectAnimator : EffectAnimatorBase<IDropShadowEffect>
+internal class DropShadowEffectAnimator : EffectAnimatorBase<IDropShadowEffect>
 {
     private static readonly DoubleAnimator s_doubleAnimator = new DoubleAnimator();
 

src/Avalonia.Base/Media/Effects/EffectTransition.cs

@@ -50,7 +50,7 @@ public class EffectTransition : Transition<IEffect?>
 
     }
 
-    public override IObservable<IEffect?> DoTransition(IObservable<double> progress, IEffect? oldValue, IEffect? newValue)
+    internal override IObservable<IEffect?> DoTransition(IObservable<double> progress, IEffect? oldValue, IEffect? newValue)
     {
         if ((oldValue != null || newValue != null)
             && (

src/Avalonia.Base/Media/GeometryDrawing.cs

@@ -7,7 +7,7 @@ namespace Avalonia.Media
     /// Represents a drawing operation that combines 
     /// a geometry with and brush and/or pen to produce rendered content.
     /// </summary>
-    public class GeometryDrawing : Drawing
+    public sealed class GeometryDrawing : Drawing
     {
         // Adding the Pen's stroke thickness here could yield wrong results due to transforms.
         private static readonly IPen s_boundsPen = new ImmutablePen(Colors.Black.ToUInt32(), 0);

src/Avalonia.Base/Media/GlyphRunDrawing.cs

@@ -1,6 +1,6 @@
 namespace Avalonia.Media
 {
-    public class GlyphRunDrawing : Drawing
+    public sealed class GlyphRunDrawing : Drawing
     {
         public static readonly StyledProperty<IBrush?> ForegroundProperty =
             AvaloniaProperty.Register<GlyphRunDrawing, IBrush?>(nameof(Foreground));

src/Avalonia.Base/Media/GradientBrush.cs

@@ -37,7 +37,7 @@ namespace Avalonia.Media
         /// </summary>
         [System.Diagnostics.CodeAnalysis.SuppressMessage("AvaloniaProperty", "AVP1012", 
             Justification = "Collection properties shouldn't be set with SetCurrentValue.")]
-        public GradientBrush()
+        internal GradientBrush()
         {
             this.GradientStops = new GradientStops();
         }

src/Avalonia.Base/Media/ImageBrush.cs

@@ -10,7 +10,7 @@ namespace Avalonia.Media
     /// <summary>
     /// Paints an area with an <see cref="IBitmap"/>.
     /// </summary>
-    public class ImageBrush : TileBrush, IImageBrush, IMutableBrush
+    public sealed class ImageBrush : TileBrush, IImageBrush, IMutableBrush
     {
         /// <summary>
         /// Defines the <see cref="Visual"/> property.

src/Avalonia.Base/Media/ImageDrawing.cs

@@ -5,7 +5,7 @@ namespace Avalonia.Media
     /// <summary>
     /// Draws an image within a region defined by a <see cref="Rect"/>.
     /// </summary>
-    public class ImageDrawing : Drawing
+    public sealed class ImageDrawing : Drawing
     {
         /// <summary>
         /// Defines the <see cref="ImageSource"/> property.

src/Avalonia.Base/Media/MatrixTransform.cs

@@ -7,7 +7,7 @@ namespace Avalonia.Media
     /// <summary>
     /// Transforms an <see cref="Visual"/> according to a <see cref="Matrix"/>.
     /// </summary>
-    public class MatrixTransform : Transform
+    public sealed class MatrixTransform : Transform
     {
         /// <summary>
         /// Defines the <see cref="Matrix"/> property.

src/Avalonia.Base/Media/MediaContext.Clock.cs

@@ -0,0 +1,53 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using Avalonia.Animation;
+using Avalonia.Reactive;
+using Avalonia.Threading;
+
+namespace Avalonia.Media;
+
+internal partial class MediaContext
+{
+    private readonly MediaContextClock _clock;
+    public IGlobalClock Clock => _clock;
+    private readonly Stopwatch _time = Stopwatch.StartNew();
+    
+    class MediaContextClock : IGlobalClock
+    {
+        private readonly MediaContext _parent;
+        private List<IObserver<TimeSpan>> _observers = new();
+        public bool HasNewSubscriptions { get; set; }
+        public bool HasSubscriptions => _observers.Count > 0;
+
+        public MediaContextClock(MediaContext parent)
+        {
+            _parent = parent;
+        }
+
+        public IDisposable Subscribe(IObserver<TimeSpan> observer)
+        {
+            _parent.ScheduleRender(false);
+            Dispatcher.UIThread.VerifyAccess();
+            HasNewSubscriptions = true;
+            _observers.Add(observer);
+            return Disposable.Create(() =>
+            {
+                Dispatcher.UIThread.VerifyAccess();
+                _observers.Remove(observer);
+            });
+        }
+
+        public void Pulse(TimeSpan now)
+        {
+            foreach (var observer in _observers.ToArray())
+                observer.OnNext(now);
+        }
+
+        public PlayState PlayState
+        {
+            get => PlayState.Run;
+            set => throw new InvalidOperationException();
+        }
+    }
+}

src/Avalonia.Base/Media/MediaContext.Compositor.cs

@@ -0,0 +1,135 @@
+using System;
+using System.Threading.Tasks;
+using Avalonia.Platform;
+using Avalonia.Rendering.Composition;
+using Avalonia.Rendering.Composition.Transport;
+using Avalonia.Threading;
+
+namespace Avalonia.Media;
+
+partial class MediaContext
+{
+    private bool _scheduleCommitOnLastCompositionBatchCompletion;
+    
+    /// <summary>
+    /// Actually sends the current batch to the compositor and does the required housekeeping
+    /// This is the only place that should be allowed to call Commit
+    /// </summary>
+    private Batch CommitCompositor(Compositor compositor)
+    {
+        var commit = compositor.Commit();
+        _requestedCommits.Remove(compositor);
+        _pendingCompositionBatches[compositor] = commit;
+        commit.Processed.ContinueWith(_ =>
+            Dispatcher.UIThread.Post(() => CompositionBatchFinished(compositor, commit), DispatcherPriority.Send));
+        return commit;
+    }
+    
+    /// <summary>
+    /// Handles batch completion, required to re-schedule a render pass if one was skipped due to compositor throttling
+    /// </summary>
+    private void CompositionBatchFinished(Compositor compositor, Batch batch)
+    {
+        // Check if it was the last commited batch, since sometimes we are forced to send a new
+        // one without waiting for the previous one to complete  
+        if (_pendingCompositionBatches.TryGetValue(compositor, out var waitingForBatch) && waitingForBatch == batch)
+            _pendingCompositionBatches.Remove(compositor);
+
+        if (_pendingCompositionBatches.Count == 0)
+        {
+            _animationsAreWaitingForComposition = false;
+
+            // Check if we have uncommited changes
+            if (_scheduleCommitOnLastCompositionBatchCompletion && _pendingCompositionBatches.Count > 0)
+            {
+                CommitCompositorsWithThrottling();
+                _scheduleCommitOnLastCompositionBatchCompletion = false;
+            }
+            // Check if there are active animations and schedule the next render
+            else if(_clock.HasSubscriptions) 
+                ScheduleRender(false);
+        }
+
+    }
+
+    private bool CommitCompositorsWithThrottling()
+    {
+        // Check if we are still waiting for previous composition batches
+        if (_pendingCompositionBatches.Count > 0)
+        {
+            _scheduleCommitOnLastCompositionBatchCompletion = true;
+            return true;
+        }
+
+        if (_requestedCommits.Count == 0)
+            return false;
+        
+        foreach (var c in _requestedCommits)
+            CommitCompositor(c);
+        
+        _requestedCommits.Clear();
+        return true;
+    }
+    
+    /// <summary>
+    /// Executes a synchronous commit when we need to wait for composition jobs to be done
+    /// Is used in resize and TopLevel destruction scenarios
+    /// </summary>
+    private void SyncCommit(Compositor compositor, bool waitFullRender)
+    {
+        // Unit tests are assuming that they can call any API without setting up platforms
+        if (AvaloniaLocator.Current.GetService<IPlatformRenderInterface>() == null)
+            return;
+        
+        if (compositor is
+            {
+                UseUiThreadForSynchronousCommits: false,
+                Loop.RunsInBackground: true
+            })
+        {
+            var batch = CommitCompositor(compositor);
+            (waitFullRender ? batch.Rendered : batch.Processed).Wait();
+        }
+        else
+        {
+            CommitCompositor(compositor);
+            compositor.Server.Render();
+        }
+    }
+    
+    /// <summary>
+    /// This method handles synchronous rendering of a surface when requested by the OS (typically during the resize)
+    /// </summary>
+    // TODO: do we need to execute a render pass here too?
+    // We've previously tried that and it made the resize experience worse
+    public void ImmediateRenderRequested(CompositionTarget target)
+    {
+        SyncCommit(target.Compositor, true);
+    }
+
+
+    /// <summary>
+    /// This method handles synchronous destruction of the composition target, so we are guaranteed
+    /// to release all resources when a TopLevel is being destroyed 
+    /// </summary>
+    public void SyncDisposeCompositionTarget(CompositionTarget compositionTarget)
+    {
+        compositionTarget.Dispose();
+        
+        // TODO: introduce a way to skip any actual rendering for other targets and only do a dispose?
+        SyncCommit(compositionTarget.Compositor, false);
+    }
+    
+    /// <summary>
+    /// This method schedules a render when something has called RequestCommitAsync
+    /// This can be triggered by user code outside of our normal layout and rendering
+    /// </summary>
+    void ICompositorScheduler.CommitRequested(Compositor compositor)
+    {
+        if(!_requestedCommits.Add(compositor))
+            return;
+
+        // TODO: maybe skip the full render here?
+        ScheduleRender(true);
+    }
+}

src/Avalonia.Base/Media/MediaContext.cs

@@ -0,0 +1,171 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Avalonia.Animation;
+using Avalonia.Layout;
+using Avalonia.Rendering;
+using Avalonia.Rendering.Composition;
+using Avalonia.Rendering.Composition.Transport;
+using Avalonia.Threading;
+
+namespace Avalonia.Media;
+
+internal partial class MediaContext : ICompositorScheduler
+{
+    private DispatcherOperation? _nextRenderOp;
+    private DispatcherOperation? _inputMarkerOp;
+    private TimeSpan _inputMarkerAddedAt;
+    private bool _animationsAreWaitingForComposition;
+    private const double MaxSecondsWithoutInput = 1;
+    private readonly Action _render;
+    private readonly Action _inputMarkerHandler;
+    private readonly HashSet<Compositor> _requestedCommits = new();
+    private readonly Dictionary<Compositor, Batch> _pendingCompositionBatches = new();
+    private record  TopLevelInfo(Compositor Compositor, CompositingRenderer Renderer, ILayoutManager LayoutManager);
+    private readonly HashSet<LayoutManager> _queuedLayoutManagers = new();
+    public static bool InputMarkerEnabled = true;
+
+    private Dictionary<object, TopLevelInfo> _topLevels = new();
+
+    private MediaContext()
+    {
+        _render = Render;
+        _inputMarkerHandler = InputMarkerHandler;
+        _clock = new(this);
+    }
+    
+    public static MediaContext Instance
+    {
+        get
+        {
+            // Technically it's supposed to be a thread-static singleton, but we don't have multiple threads
+            // and need to do a full reset for unit tests
+            var context = AvaloniaLocator.Current.GetService<MediaContext>();
+            if (context == null)
+                AvaloniaLocator.CurrentMutable.Bind<MediaContext>().ToConstant(context = new());
+            return context;
+        }
+    }
+    
+    /// <summary>
+    /// Schedules the next render operation, handles render throttling for input processing
+    /// </summary>
+    private void ScheduleRender(bool now)
+    {
+        // Already scheduled, nothing to do
+        if (_nextRenderOp != null)
+        {
+            if (now)
+                _nextRenderOp.Priority = DispatcherPriority.Render;
+            return;
+        }
+        // Sometimes our animation, layout and render passes might be taking more than a frame to complete
+        // which can cause a "freeze"-like state when UI is being updated, but input is never being processed
+        // So here we inject an operation with Input priority to check if Input wasn't being processed
+        // for a long time. If that's the case the next rendering operation will be scheduled to happen after all pending input
+        
+        var priority = DispatcherPriority.Render;
+        
+        if (InputMarkerEnabled)
+        {
+            if (_inputMarkerOp == null)
+            {
+                _inputMarkerOp = Dispatcher.UIThread.InvokeAsync(_inputMarkerHandler, DispatcherPriority.Input);
+                _inputMarkerAddedAt = _time.Elapsed;
+            }
+            else if (!now && (_time.Elapsed - _inputMarkerAddedAt).TotalSeconds > MaxSecondsWithoutInput)
+            {
+                priority = DispatcherPriority.Input;
+            }
+        }
+
+        _nextRenderOp = Dispatcher.UIThread.InvokeAsync(_render, priority);
+    }
+    
+    /// <summary>
+    /// This handles the _inputMarkerOp message.  We're using
+    /// _inputMarkerOp to determine if input priority dispatcher ops
+    /// have been processes.
+    /// </summary>
+    private void InputMarkerHandler()
+    {
+        //set the marker to null so we know that input priority has been processed
+        _inputMarkerOp = null;
+    }
+
+    private void Render()
+    {
+        try
+        {
+            RenderCore();
+        }
+        finally
+        {
+            _nextRenderOp = null;
+        }
+    }
+    
+    private void RenderCore()
+    {
+        var now = _time.Elapsed;
+        if (!_animationsAreWaitingForComposition)
+            _clock.Pulse(now);
+
+        // Since new animations could be started during the layout and can affect layout/render
+        // We are doing several iterations when it happens
+        for (var c = 0; c < 10; c++)
+        {
+            _clock.HasNewSubscriptions = false;
+            //TODO: Integrate LayoutManager's attempt limit here
+            foreach (var layout in _queuedLayoutManagers.ToArray())
+                layout.ExecuteQueuedLayoutPass();
+            _queuedLayoutManagers.Clear();
+            
+            if (_clock.HasNewSubscriptions)
+            {
+                _clock.Pulse(now);
+                continue;
+            }
+
+            break;
+        }
+
+        // We are currently using compositor commit callbacks to drive animations
+        // Later we should use WPF's approach that asks the animation system for the next tick time
+        // and use some timer if the next animation frame is not needed to be sent to the compositor immediately
+        if (_requestedCommits.Count > 0 || _clock.HasSubscriptions)
+        {
+            _animationsAreWaitingForComposition = true;
+            CommitCompositorsWithThrottling();
+        }
+    }
+
+    // Used for unit tests
+    public bool IsTopLevelActive(object key) => _topLevels.ContainsKey(key);
+
+    public void AddTopLevel(object key, ILayoutManager layoutManager, IRenderer renderer)
+    {
+        if(_topLevels.ContainsKey(key))
+            return;
+        var render = (CompositingRenderer)renderer;
+        _topLevels.Add(key, new TopLevelInfo(render.Compositor, render, layoutManager));
+        render.Start();
+        ScheduleRender(true);
+    }
+
+    public void RemoveTopLevel(object key)
+    {
+        if (_topLevels.TryGetValue(key, out var info))
+        {
+            _topLevels.Remove(key);
+            info.Renderer.Stop();
+        }
+    }
+
+    public void QueueLayoutPass(LayoutManager layoutManager)
+    {
+        _queuedLayoutManagers.Add(layoutManager);
+        ScheduleRender(true);
+    }
+}

src/Avalonia.Base/Media/RotateTransform.cs

@@ -7,7 +7,7 @@ namespace Avalonia.Media
     /// <summary>
     /// Rotates an <see cref="Visual"/>.
     /// </summary>
-    public class RotateTransform : Transform
+    public sealed class RotateTransform : Transform
     {
         /// <summary>
         /// Defines the <see cref="Angle"/> property.