+ remove empty archetypes function

samples/MyBattleground/Program.cs

@@ -8,6 +8,34 @@
 
 using var ecs = new World();
 
+var entities = new EntityView[1];
+for (var i = 0; i < entities.Length; ++i)
+	entities[i] = ecs.Entity();
+
+foreach (var e in entities)
+{
+	e.Set(new Component1());
+	e.Set(new Component2());
+	e.Set(new Component3());
+	e.Set(new Component4());
+	e.Set(new Component5());
+}
+
+// while (true)
+// {
+// 	foreach (var e in entities)
+// 		e.Get<Component1>() = new Component1();
+
+// 	// foreach (var e in entities)
+// 	// {
+// 	// 	e.Unset<Component1>();
+// 	// 	e.Unset<Component2>();
+// 	// 	e.Unset<Component3>();
+// 	// 	e.Unset<Component4>();
+// 	// 	e.Unset<Component5>();
+// 	// }
+// }
+
 
 var asd = ecs.Entity().Set(new Position());
 var name = ecs.Entity<Position>().Name();
@@ -32,7 +60,7 @@
 child.Set(new EquippedItem() { Layer = 3 }, root);
 
 // root.AddChild(child);
-root.Delete();
+// root.Delete();
 
 ref var equip2 = ref ecs.Get<EquippedItem>(child);
 ref var equip = ref ecs.Get<EquippedItem>(child, root);
@@ -51,6 +79,9 @@
 var xx = ecs.Entity().Set(new Position() {X = 3});
 ref var qq = ref xx.Get<Position>();
 
+
+ecs.RemoveEmptyArchetypes();
+
 var query = ecs.Query<(Position, Velocity)>();
 
 // foreach (var (pos, vel) in query.Iter<Position, Velocity>())
@@ -250,6 +281,13 @@
 var scheduler = new Scheduler(ecs);
 scheduler.AddResource(0);
 
+void initWnd(Query<int> query)
+{
+
+}
+
+scheduler.AddSystem<Query<int>>(initWnd, stage: Stages.Startup);
+
 scheduler.AddSystem((Res<int> res) => Console.WriteLine("system 0 - thread id {0}", Thread.CurrentThread.ManagedThreadId), threadingType: ThreadingMode.Auto);
 scheduler.AddSystem(() => Console.WriteLine("system 1 - thread id {0}", Thread.CurrentThread.ManagedThreadId), threadingType: ThreadingMode.Auto);
 
@@ -259,8 +297,8 @@
 // sysAfter.RunAfter(sys);
 // sys.RunAfter(sysAfter);
 
-while (true)
-	scheduler.Run();
+// while (true)
+// 	scheduler.Run();
 
 scheduler.AddSystem((Local<int> i32, Res<string> str, Local<string> strLocal) => {
 	Console.WriteLine(i32.Value++);
@@ -550,3 +588,15 @@ struct Networked { }
 delegate void Query2Del<T0, T1>(ref T0 t0, ref T1 t1);
 
 struct EquippedItem { public byte Layer; }
+
+
+
+public record struct Component1(int Value);
+
+public record struct Component2(int Value);
+
+public record struct Component3(int Value);
+
+public record struct Component4(int Value);
+
+public record struct Component5(int Value);

src/Archetype.cs

@@ -346,6 +346,24 @@ private void TrimChunksIfNeeded()
 			Array.Resize(ref _chunks, half);
 	}
 
+	internal void RemoveEmptyArchetypes(ref int removed, Dictionary<EcsID, Archetype> cache)
+	{
+		for (var i = _add.Count - 1; i >= 0; --i)
+		{
+			var edge = _add[i];
+			edge.Archetype.RemoveEmptyArchetypes(ref removed, cache);
+
+			if (edge.Archetype.Count == 0 && edge.Archetype._add.Count == 0)
+			{
+				cache.Remove(edge.Archetype.Id);
+				_remove.Clear();
+				_add.RemoveAt(i);
+
+				removed += 1;
+			}
+		}
+	}
+
 	private static void MakeEdges(Archetype left, Archetype right, EcsID id)
 	{
 		left._add.Add(new EcsEdge() { Archetype = right, Id = id });

src/World.Public.cs

@@ -101,6 +101,19 @@ public void Dispose()
 		_cachedQueries.Clear();
     }
 
+	/// <summary>
+	/// Remove all empty archetypes.
+	/// </summary>
+	/// <returns></returns>
+	public int RemoveEmptyArchetypes()
+	{
+		var removed = 0;
+		_archRoot?.RemoveEmptyArchetypes(ref removed, _typeIndex);
+		if (removed > 0)
+			LastArchetypeId = ulong.MaxValue;
+		return removed;
+	}
+
 	/// <summary>
 	/// Get or create an archetype with the specified components.
 	/// </summary>