Apparently LayoutKind.Sequential is ignored for generic structs

src/Avalonia.Base/Rendering/Composition/Animations/AnimatedValueStore.cs

@@ -32,11 +32,9 @@ namespace Avalonia.Rendering.Composition.Animations
     /// The value store for non-animated values that can still be referenced by animations.
     /// Simply stores the value and notifies subscribers
     /// </summary>
-    [StructLayout(LayoutKind.Sequential)]
     internal struct ServerValueStore<T>
     {
-        // HAS TO BE THE FIRST FIELD, accessed by field offset from ServerObject
-        private ServerObjectSubscriptionStore Subscriptions;
+        public ServerObjectSubscriptionStore Subscriptions;
         private T _value;
         public T Value
         {
@@ -61,8 +59,7 @@ namespace Avalonia.Rendering.Composition.Animations
     [StructLayout(LayoutKind.Sequential)]
     internal struct ServerAnimatedValueStore<T> where T : struct
     {
-        // HAS TO BE THE FIRST FIELD, accessed by field offset from ServerObject
-        private ServerObjectSubscriptionStore Subscriptions;
+        public ServerObjectSubscriptionStore Subscriptions;
         private IAnimationInstance? _animation;
         private T _direct;
         private T? _lastAnimated;

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

@@ -63,15 +63,15 @@ namespace Avalonia.Rendering.Composition.Server
         }
         
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        protected int GetOffset<T>(ref T field) where T : struct
+        protected int GetOffset(ref ServerObjectSubscriptionStore field)
         {
-            return Unsafe.ByteOffset(ref Unsafe.As<uint, object>(ref _activationCount),
-                    ref Unsafe.As<T, object>(ref field))
+            return Unsafe.ByteOffset(ref _activationCount,
+                    ref Unsafe.As<ServerObjectSubscriptionStore, uint>(ref field))
                 .ToInt32();
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        private ref ServerObjectSubscriptionStore GetStoreFromOffset(int offset)
+        protected ref ServerObjectSubscriptionStore GetStoreFromOffset(int offset)
         {
 #if DEBUG
             if (offset == 0)

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

@@ -2,7 +2,9 @@ using System;
 using System.Numerics;
 using Avalonia.Media;
 using Avalonia.Platform;
+using Avalonia.Rendering.Composition.Animations;
 using Avalonia.Rendering.Composition.Transport;
+using Avalonia.Utilities;
 
 namespace Avalonia.Rendering.Composition.Server
 {

src/tools/DevGenerators/CompositionGenerator/Generator.cs

@@ -298,7 +298,7 @@ namespace Avalonia.SourceGenerator.CompositionGenerator
                     AssignmentExpression(SyntaxKind.SimpleAssignmentExpression, IdentifierName(fieldOffsetName),
                         InvocationExpression(MemberAccess(IdentifierName(uninitializedObjectName), "GetOffset"),
                             ArgumentList(SingletonSeparatedList(Argument(
-                                RefExpression(MemberAccess(IdentifierName(uninitializedObjectName), fieldName)))))))));
+                                RefExpression(MemberAccess(MemberAccess(IdentifierName(uninitializedObjectName), fieldName), "Subscriptions")))))))));
                 
                 if (prop.DefaultValue != null)
                 {