BREAKING CHANGE: replaced universe objects with root universe object

Engine.Core/Abstract/IUniverse.cs

@@ -78,9 +78,9 @@ public interface IUniverse : IEntity, IEnumerable<IUniverseObject>
     UniverseTime UnscaledTime { get; }
 
     /// <summary>
-    /// Gets a read-only list of <see cref="IUniverseObject"/>s managed by the <see cref="IUniverse"/>.
+    /// Gets the root <see cref="IUniverseObject"/> of the <see cref="IUniverse"/>.
     /// </summary>
-    IReadOnlyList<IUniverseObject> UniverseObjects { get; }
+    IUniverseObject Root { get; }
 
     /// <summary>
     /// Registers an <see cref="IUniverseObject"/> to the <see cref="IUniverse"/>.

Engine.Core/Collectors/ActiveBehaviourCollectorBase.cs

@@ -29,7 +29,7 @@ public abstract class ActiveBehaviourCollectorBase<T> : IBehaviourCollector<T> w
         if (Universe is not null)
             return false;
 
-        foreach (IUniverseObject universeObject in universe.UniverseObjects)
+        foreach (IUniverseObject universeObject in universe)
             OnUniverseObjectRegistered(universe, new(universeObject));
 
         universe.OnUniverseObjectRegistered.AddListener(delegateOnUniverseObjectRegistered);
@@ -46,7 +46,7 @@ public abstract class ActiveBehaviourCollectorBase<T> : IBehaviourCollector<T> w
         if (Universe is null)
             return false;
 
-        foreach (IUniverseObject universeObject in Universe.UniverseObjects)
+        foreach (IUniverseObject universeObject in Universe)
             OnUniverseObjectUnregistered(Universe, new(universeObject));
 
         Universe.OnUniverseObjectRegistered.RemoveListener(delegateOnUniverseObjectRegistered);

Engine.Core/Collectors/BehaviourCollectorBase.cs

@@ -25,7 +25,7 @@ public abstract class BehaviourCollectorBase<T> : IBehaviourCollector<T> where T
         if (Universe is not null)
             return false;
 
-        foreach (IUniverseObject universeObject in universe.UniverseObjects)
+        foreach (IUniverseObject universeObject in universe)
             OnUniverseObjectRegistered(universe, new(universeObject));
 
         universe.OnUniverseObjectRegistered.AddListener(delegateOnUniverseObjectRegistered);
@@ -43,7 +43,7 @@ public abstract class BehaviourCollectorBase<T> : IBehaviourCollector<T> where T
         if (Universe is null)
             return false;
 
-        foreach (IUniverseObject universeObject in Universe.UniverseObjects)
+        foreach (IUniverseObject universeObject in Universe)
             OnUniverseObjectUnregistered(Universe, new(universeObject));
 
         Universe.OnUniverseObjectRegistered.RemoveListener(delegateOnUniverseObjectRegistered);

Engine.Core/Extensions/UniverseExtensions.cs

@@ -32,5 +32,5 @@ public static class UniverseExtensions
     /// <typeparam name="T">Type to be searched through the <see cref="IUniverse"/>.</typeparam>
     /// <returns>The specified type if found; otherwise, throws <see cref="NotFoundException"/>.</returns>
     public static T FindRequired<T>(this IUniverse universe) where T : class
-        => universe.Find<T>() ?? throw new NotFoundException($"{universe.GetType().FullName}({universe.Id}) does not contain any {nameof(IUniverseObject)} or {nameof(IBehaviour)} of type {typeof(T).FullName}");
+        => universe.Root.BehaviourController.GetBehaviourInChildren<T>() ?? throw new NotFoundException($"{universe.GetType().FullName}({universe.Id}) does not contain any {nameof(IUniverseObject)} or {nameof(IBehaviour)} of type {typeof(T).FullName}");
 }

Engine.Core/Extensions/UniverseObjectExtensions.cs

@@ -16,6 +16,21 @@ public static class UniverseObjectExtensions
         return universeObject;
     }
 
+    public static IEnumerator<IUniverseObject> TraverseChildren(this IUniverseObject universeObject)
+    {
+        static IEnumerable<IUniverseObject> Traverse(IUniverseObject obj)
+        {
+            foreach (IUniverseObject child in obj.Children)
+            {
+                yield return child;
+                foreach (IUniverseObject descendant in Traverse(child))
+                    yield return descendant;
+            }
+        }
+
+        return Traverse(universeObject).GetEnumerator();
+    }
+
     #region Universe Object Search
     /// <summary>
     /// Gets a <see cref="IUniverseObject"/> of the specified type.

Engine.Core/Systems/UniverseEntranceManager.cs

@@ -23,7 +23,7 @@ public class UniverseEntranceManager : Internal.BehaviourIndependent
         enterUniverses.Assign(universe);
         exitUniverses.Assign(universe);
 
-        foreach (IUniverseObject universeObject in universe.UniverseObjects)
+        foreach (IUniverseObject universeObject in universe)
             OnUniverseObjectRegistered(universe, new(universeObject));
 
         universe.OnUniverseObjectRegistered.AddListener(OnUniverseObjectRegistered);
@@ -35,7 +35,7 @@ public class UniverseEntranceManager : Internal.BehaviourIndependent
         enterUniverses.Unassign();
         exitUniverses.Unassign();
 
-        foreach (IUniverseObject universeObject in universe.UniverseObjects)
+        foreach (IUniverseObject universeObject in universe)
             OnUniverseObjectUnRegistered(universe, new(universeObject));
 
         universe.OnUniverseObjectRegistered.RemoveListener(OnUniverseObjectRegistered);

Engine.Core/Universe.cs

@@ -31,7 +31,7 @@ public class Universe : BaseEntity, IUniverse
         delegateOnUniverseObjectExitedUniverse = OnUniverseObjectExitedUniverse;
     }
 
-    public IReadOnlyList<IUniverseObject> UniverseObjects => _universeObjects;
+    public IUniverseObject Root { get; private set; } = Factory.UniverseObjectFactory.Instantiate().SetUniverseObject("Root");
 
     public UniverseTime Time { get; private set; } = new();
     public UniverseTime UnscaledTime { get; private set; } = new();
@@ -68,6 +68,9 @@ public class Universe : BaseEntity, IUniverse
 
         _universeObjects.Add(universeObject);
 
+        if (universeObject.Parent == null)
+            universeObject.Parent = Root;
+
         if (!universeObject.EnterUniverse(this))
             throw new Exception($"{universeObject.Name} can't enter the universe");
 
@@ -113,15 +116,15 @@ public class Universe : BaseEntity, IUniverse
 
     protected override void InitializeInternal()
     {
-        foreach (IUniverseObject universeObject in UniverseObjects)
+        foreach (IUniverseObject universeObject in _universeObjects)
             universeObject.Initialize();
     }
 
     protected override void FinalizeInternal()
     {
         base.FinalizeInternal();
-        for (int i = UniverseObjects.Count - 1; i >= 0; i--)
+        for (int i = _universeObjects.Count - 1; i >= 0; i--)
-            Remove(UniverseObjects[i]);
+            Remove(_universeObjects[i]);
     }
 
     public void Update(UniverseTime engineTime)
@@ -158,6 +161,6 @@ public class Universe : BaseEntity, IUniverse
             Remove(universeObject);
     }
 
-    public IEnumerator<IUniverseObject> GetEnumerator() => _universeObjects.GetEnumerator();
+    public IEnumerator<IUniverseObject> GetEnumerator() => Root.TraverseChildren();
-    IEnumerator IEnumerable.GetEnumerator() => _universeObjects.GetEnumerator();
+    IEnumerator IEnumerable.GetEnumerator() => Root.TraverseChildren();
 }

Engine.Integration/Engine.Integration.Yaml/Converters/UniverseConverter.cs

@@ -22,7 +22,7 @@ public class UniverseConverter : EngineTypeYamlSerializerBase<IUniverse>
 
         IUniverse universe;
         IStateEnable stateEnable;
-        List<IUniverseObject> universeObjects;
+        IUniverseObject rootUniverseObject;
 
         parser.Consume<MappingStart>();
 
@@ -34,16 +34,16 @@ public class UniverseConverter : EngineTypeYamlSerializerBase<IUniverse>
             throw new();
         SerializedClass instanceSerializedClass = (SerializedClass)rootDeserializer(typeof(SerializedClass))!;
         ProgressionTracker.Set(isTrackingController ? .2f : ProgressionTracker.Progression, $"Creating {instanceSerializedClass.Type}");
-        universe = (IUniverse)instanceSerializedClass.CreateInstance(EntityRegistry);
+        universe = (IUniverse)instanceSerializedClass.CreateInstance(IdentifiableRegistry);
 
         if (parser.Consume<Scalar>().Value.CompareTo(nameof(IUniverse.StateEnable)) != 0)
             throw new();
         stateEnable = (IStateEnable)rootDeserializer(typeof(IStateEnable))!;
 
         ProgressionTracker.Set(isTrackingController ? .5f : ProgressionTracker.Progression, $"Reading universe objects");
-        if (parser.Consume<Scalar>().Value.CompareTo(nameof(IUniverse.UniverseObjects)) != 0)
+        if (parser.Consume<Scalar>().Value.CompareTo(nameof(IUniverse.Root)) != 0)
             throw new();
-        universeObjects = (List<IUniverseObject>)rootDeserializer(typeof(List<IUniverseObject>))!;
+        rootUniverseObject = (IUniverseObject)rootDeserializer(typeof(IUniverseObject))!;
 
         parser.Consume<MappingEnd>();
 
@@ -52,13 +52,12 @@ public class UniverseConverter : EngineTypeYamlSerializerBase<IUniverse>
         stateEnable.Assign(universe);
         universe.Assign(stateEnable);
 
-        ProgressionTracker.Set(isTrackingController ? .9f : ProgressionTracker.Progression, "Registering universe objects");
+        ProgressionTracker.Set(isTrackingController ? .9f : ProgressionTracker.Progression, "Registering root universe object");
-        for (int i = 0; i < universeObjects.Count; i++)
+        for (int i = 0; i < rootUniverseObject.Children.Count; i++)
         {
-            IUniverseObject uo = universeObjects[i];
+            IUniverseObject uo = rootUniverseObject.Children[i];
-            ProgressionTracker.Set(isTrackingController ? .9f + .1f * ((float)i / universeObjects.Count) : ProgressionTracker.Progression, $"Registering {uo.Name}");
+            ProgressionTracker.Set(isTrackingController ? .9f + .1f * ((float)i / rootUniverseObject.Children.Count) : ProgressionTracker.Progression, $"Registering {uo.Name}");
-
+            universe.Root.AddChild(uo);
-            universe.Register(uo);
         }
 
         ProgressionTracker.Set(isTrackingController ? 1f : ProgressionTracker.Progression, $"Created {instanceSerializedClass.Type}");
@@ -72,7 +71,7 @@ public class UniverseConverter : EngineTypeYamlSerializerBase<IUniverse>
         bool isTrackingController = ProgressionTracker.Progression.ApproximatelyEquals(0f);
         ProgressionTracker.Set(isTrackingController ? .25f : ProgressionTracker.Progression, $"Serializing universe");
 
-        IEnumerable<IUniverseObject> rootUniverseObjects = universe.UniverseObjects.Where(uo => uo.Parent is null);
+        IUniverseObject rootUniverseObject = universe.Root;
 
         emitter.Emit(new MappingStart());
 
@@ -85,8 +84,8 @@ public class UniverseConverter : EngineTypeYamlSerializerBase<IUniverse>
         emitter.Emit(new Scalar(nameof(IUniverse.StateEnable)));
         serializer(universe.StateEnable);
 
-        emitter.Emit(new Scalar(nameof(IUniverse.UniverseObjects)));
+        emitter.Emit(new Scalar(nameof(IUniverse.Root)));
-        serializer(rootUniverseObjects);
+        serializer(rootUniverseObject);
 
         ProgressionTracker.Set(isTrackingController ? 1f : ProgressionTracker.Progression, $"Serialized universe");
         emitter.Emit(new MappingEnd());

Engine.Integration/Engine.Integration.Yaml/Converters/UniverseObjectConverter.cs

@@ -97,7 +97,7 @@ public class UniverseObjectSerializer : EngineTypeYamlSerializerBase<IUniverseOb
         serializer(universeObject.BehaviourController);
 
         emitter.Emit(new Scalar(nameof(IUniverseObject.Children)));
-        serializer(universeObject.Children.Where(c => !c.GetType().HasAttribute<IgnoreSerializationAttribute>()));
+        serializer(universeObject.Children.Where(c => !c.GetType().HasAttribute<IgnoreSerializationAttribute>()).Reverse());
 
         ProgressionTracker.Set(isTrackingController ? 1f : ProgressionTracker.Progression, $"Serializing universe object");
         emitter.Emit(new MappingEnd());