Add Actor.Clone for actors duplication at runtime (including scripts and children)

#2012

Source/Engine/Level/Actor.cpp

@@ -3,6 +3,7 @@
 #include "Actor.h"
 #include "ActorsCache.h"
 #include "Level.h"
+#include "SceneQuery.h"
 #include "SceneObjectsFactory.h"
 #include "Scene/Scene.h"
 #include "Prefabs/Prefab.h"
@@ -1880,8 +1881,7 @@ String Actor::ToJson()
     CompactJsonWriter writer(buffer);
     writer.SceneObject(this);
     String result;
-    const char* c = buffer.GetString();
-    result.SetUTF8(c, (int32)buffer.GetSize());
+    result.SetUTF8(buffer.GetString(), (int32)buffer.GetSize());
     return result;
 }
 
@@ -1909,6 +1909,41 @@ void Actor::FromJson(const StringAnsiView& json)
     OnTransformChanged();
 }
 
+Actor* Actor::Clone()
+{
+    // Collect actors to clone
+    auto actors = ActorsCache::ActorsListCache.Get();
+    actors->Add(this);
+    SceneQuery::GetAllActors(this, *actors);
+
+    // Serialize objects
+    MemoryWriteStream stream;
+    if (ToBytes(*actors, stream))
+        return nullptr;
+
+    // Remap object ids into a new ones
+    auto modifier = Cache::ISerializeModifier.Get();
+    for (int32 i = 0; i < actors->Count(); i++)
+    {
+        auto actor = actors->At(i);
+        if (!actor)
+            continue;
+        modifier->IdsMapping.Add(actor->GetID(), Guid::New());
+        for (int32 j = 0; j < actor->Scripts.Count(); j++)
+        {
+            const auto script = actor->Scripts[j];
+            if (script)
+                modifier->IdsMapping.Add(script->GetID(), Guid::New());
+        }
+    }
+
+    // Deserialize objects
+    Array<Actor*> output;
+    if (FromBytes(ToSpan(stream.GetHandle(), (int32)stream.GetPosition()), output, modifier.Value) || output.IsEmpty())
+        return nullptr;
+    return output[0];
+}
+
 void Actor::SetPhysicsScene(PhysicsScene* scene)
 {
     CHECK(scene);

Source/Engine/Level/Actor.h

@@ -982,6 +982,11 @@ public:
     /// <param name="json">The serialized actor data (state).</param>
     API_FUNCTION() void FromJson(const StringAnsiView& json);
 
+    /// <summary>
+    /// Clones actor including all scripts and any child actors (whole scene tree). Objects are duplicated via serialization (any transient/non-saved state is ignored).
+    /// </summary>
+    API_FUNCTION() Actor* Clone();
+
 public:
     /// <summary>
     /// Called when actor gets added to game systems. Occurs on BeginPlay event or when actor gets activated in hierarchy. Use this event to register object to other game system (eg. audio).