Fix duplicating spline

#452

Source/Editor/SceneGraph/Actors/SplineNode.cs

@@ -29,7 +29,7 @@ namespace FlaxEditor.SceneGraph.Actors
 
             public override bool CanBeSelectedDirectly => true;
 
-            public override bool CanDuplicate => true;
+            public override bool CanDuplicate => !Root?.Selection.Contains(ParentNode) ?? true;
 
             public override bool CanDelete => true;
 

Source/Editor/SceneGraph/RootNode.cs

@@ -1,6 +1,7 @@
 // Copyright (c) 2012-2021 Wojciech Figat. All rights reserved.
 
 using System;
+using System.Collections.Generic;
 using FlaxEditor.SceneGraph.Actors;
 using FlaxEngine;
 
@@ -146,5 +147,10 @@ namespace FlaxEditor.SceneGraph
         /// Gets the undo.
         /// </summary>
         public abstract Undo Undo { get; }
+
+        /// <summary>
+        /// Gets the list of selected scene graph nodes in the editor context.
+        /// </summary>
+        public abstract List<SceneGraphNode> Selection { get; }
     }
 }

Source/Editor/SceneGraph/SceneGraphNode.cs

@@ -57,7 +57,9 @@ namespace FlaxEditor.SceneGraph
         /// </summary>
         public virtual RootNode Root => ParentNode?.Root;
 
-        /// <inheritdoc />
+        /// <summary>
+        /// Gets or sets the transform of the node.
+        /// </summary>
         public abstract Transform Transform { get; set; }
 
         /// <summary>