Add initial Behavior simulation

Source/Engine/AI/BehaviorTree.cs

@@ -1,5 +1,7 @@
 // Copyright (c) 2012-2023 Wojciech Figat. All rights reserved.
 
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
 #if FLAX_EDITOR
 using System;
 using FlaxEngine.Utilities;
@@ -39,4 +41,55 @@ namespace FlaxEngine
         }
 #endif
     }
+
+    unsafe partial class BehaviorTreeNode
+    {
+        /// <summary>
+        /// Gets the size in bytes of the given typed node state structure.
+        /// </summary>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static int GetStateSize<T>()
+        {
+            // C# nodes state is stored via pinned GCHandle to support holding managed references (eg. string or Vector3[])
+            return sizeof(IntPtr);
+        }
+
+        /// <summary>
+        /// Sets the node state at the given memory address.
+        /// </summary>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public void AllocState(IntPtr memory, object state)
+        {
+            var handle = GCHandle.Alloc(state);
+            var ptr = IntPtr.Add(memory, _memoryOffset).ToPointer();
+            Unsafe.Write<IntPtr>(ptr, (IntPtr)handle);
+        }
+
+        /// <summary>
+        /// Returns the typed node state at the given memory address.
+        /// </summary>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public ref T GetState<T>(IntPtr memory) where T : struct
+        {
+            var ptr = IntPtr.Add(memory, _memoryOffset).ToPointer();
+            var handle = GCHandle.FromIntPtr(Unsafe.Read<IntPtr>(ptr));
+            var state = handle.Target;
+#if !BUILD_RELEASE
+            if (state == null)
+                throw new NullReferenceException();
+#endif
+            return ref Unsafe.Unbox<T>(state);
+        }
+
+        /// <summary>
+        /// Frees the allocated node state at the given memory address.
+        /// </summary>
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public void FreeState(IntPtr memory)
+        {
+            var ptr = IntPtr.Add(memory, _memoryOffset).ToPointer();
+            var handle = GCHandle.FromIntPtr(Unsafe.Read<IntPtr>(ptr));
+            handle.Free();
+        }
+    }
 }