From 06dbf6c9874ff39492a2875822ee4ae813d1217f Mon Sep 17 00:00:00 2001
From: Ullrich Praetz <ullrich@praetz.de>
Date: Fri, 19 Jul 2024 12:47:36 +0200
Subject: [PATCH] Engine - ECS: make TreeNode blittable

---
 Engine/src/ECS/Components/TreeNode.cs   |  1 -
 Engine/src/ECS/Entity/Store/Entities.cs | 10 ++++++++--
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/Engine/src/ECS/Components/TreeNode.cs b/Engine/src/ECS/Components/TreeNode.cs
index c55dd8129..c1bda3ffd 100644
--- a/Engine/src/ECS/Components/TreeNode.cs
+++ b/Engine/src/ECS/Components/TreeNode.cs
@@ -16,7 +16,6 @@ public struct TreeNode : IComponent    // todo should be internal
     
 //  [Browse(Never)] internal    int         parentId;   //  4   0 if entity has no parent
                     internal    IdArray     childIds;   //  8
-                    internal    int[]       dummy;      //  8  todo remove
     
     /// same as <see cref="IdArrayExtensions.GetSpan"/>
     public ReadOnlySpan<int>  GetChildIds(EntityStore store)
diff --git a/Engine/src/ECS/Entity/Store/Entities.cs b/Engine/src/ECS/Entity/Store/Entities.cs
index f2ae13ebb..a35768ae3 100644
--- a/Engine/src/ECS/Entity/Store/Entities.cs
+++ b/Engine/src/ECS/Entity/Store/Entities.cs
@@ -81,7 +81,10 @@ internal int CreateEntityInternal(Archetype archetype, int id)
     /// <summary>
     /// Create and return a clone of the passed <paramref name="entity"/> in the store.
     /// </summary>
-    /// <returns></returns>
+    /// <remarks>
+    /// Child entities of the passed <paramref name="entity"/> are not copied to the cloned entity.<br/>
+    /// If doing this these child entities would be children of the passed entity <b>and</b> the clone.
+    /// </remarks>
     public Entity CloneEntity(Entity entity)
     {
         var archetype   = entity.archetype ?? throw EntityNullException(entity);
@@ -96,6 +99,9 @@ public Entity CloneEntity(Entity entity)
             var scriptTypeByType    = Static.EntitySchema.ScriptTypeByType;
             // CopyComponents() must be used only in case all component types are blittable
             Archetype.CopyComponents(archetype, entity.compIndex, clone.compIndex);
+            if (clone.HasComponent<TreeNode>()) {
+                clone.GetComponent<TreeNode>() = default;   // clear child ids. See child entities note in remarks.
+            }
             // --- clone scripts
             foreach (var script in entity.Scripts) {
                 var scriptType      = scriptTypeByType[script.GetType()];
@@ -110,7 +116,7 @@ public Entity CloneEntity(Entity entity)
             
             // --- deserialize DataEntity
             dataBuffer.pid      = IdToPid(clone.Id);
-            dataBuffer.children = null; // child ids are not copied. If doing this these children would have two parents.
+            dataBuffer.children = null;                     // clear children. See child entities note in remarks.
             // convert will use entity created above
             converter.DataEntityToEntity(dataBuffer, this, out string error); // error == null. No possibility for mapping errors
             AssertNoError(error);