start implementing world transfer

src/ComponentDepot.cs

@@ -103,7 +103,17 @@ namespace MoonTools.ECS
 
 		public void CreateMissingStorages(ComponentDepot other)
 		{
-			for (var i = 0; i < ComponentTypeIndices.Count; i += 1)
+			while (other.ComponentTypeIndices.Count >= storages.Length)
+			{
+				Array.Resize(ref storages, storages.Length * 2);
+			}
+
+			while (other.ComponentTypeIndices.Count >= other.storages.Length)
+			{
+				Array.Resize(ref other.storages, other.storages.Length * 2);
+			}
+
+			for (var i = 0; i < other.ComponentTypeIndices.Count; i += 1)
 			{
 				if (storages[i] == null && other.storages[i] != null)
 				{

src/EntityComponentReader.cs

@@ -20,6 +20,11 @@ namespace MoonTools.ECS
 			World = world;
 		}
 
+		protected string GetTag(in Entity entity)
+		{
+			return World.GetTag(entity);
+		}
+
 		protected ReadOnlySpan<TComponent> ReadComponents<TComponent>() where TComponent : unmanaged
 		{
 			return ComponentDepot.ReadComponents<TComponent>();

src/EntityStorage.cs

@@ -15,17 +15,24 @@ namespace MoonTools.ECS
 
 		public int Count => nextID - availableIDs.Count;
 
-		public Entity Create()
+		public Dictionary<int, string> Tags = new Dictionary<int, string>();
+
+		public Entity Create(string tag)
 		{
 			var entity = new Entity(NextID());
+
 			if (!EntityToComponentTypeIndices.ContainsKey(entity.ID))
 			{
 				EntityToComponentTypeIndices.Add(entity.ID, new HashSet<int>());
 			}
+
 			if (!EntityToRelationTypeIndices.ContainsKey(entity.ID))
 			{
 				EntityToRelationTypeIndices.Add(entity.ID, new HashSet<int>());
 			}
+
+			Tags[entity.ID] = tag;
+
 			return entity;
 		}
 
@@ -34,10 +41,16 @@ namespace MoonTools.ECS
 			return Taken(entity.ID);
 		}
 
+		public void Tag(in Entity entity, string tag)
+		{
+			Tags[entity.ID] = tag;
+		}
+
 		public void Destroy(in Entity entity)
 		{
 			EntityToComponentTypeIndices[entity.ID].Clear();
 			EntityToRelationTypeIndices[entity.ID].Clear();
+			Tags.Remove(entity.ID);
 			Release(entity.ID);
 		}
 
@@ -68,6 +81,11 @@ namespace MoonTools.ECS
 			EntityToRelationTypeIndices[entityId].Remove(relationIndex);
 		}
 
+		public string Tag(int entityID)
+		{
+			return Tags[entityID];
+		}
+
 		public HashSet<int> ComponentTypeIndices(int entityID)
 		{
 			return EntityToComponentTypeIndices[entityID];

src/Manipulator.cs

@@ -6,7 +6,8 @@ namespace MoonTools.ECS
 		{
 		}
 
-		protected Entity CreateEntity() => World.CreateEntity();
+		protected Entity CreateEntity(string tag = "") => World.CreateEntity(tag);
+		protected void Tag(Entity entity, string tag) => World.Tag(entity, tag);
 		protected void Set<TComponent>(in Entity entity, in TComponent component) where TComponent : unmanaged => World.Set<TComponent>(entity, component);
 		protected void Remove<TComponent>(in Entity entity) where TComponent : unmanaged => World.Remove<TComponent>(entity);
 		protected void Relate<TRelationKind>(in Entity entityA, in Entity entityB, TRelationKind relationData) where TRelationKind : unmanaged => World.Relate(entityA, entityB, relationData);

src/RelationDepot.cs

@@ -156,7 +156,17 @@ namespace MoonTools.ECS
 
 		public void CreateMissingStorages(RelationDepot other)
 		{
-			for (var i = 0; i < RelationTypeIndices.Count; i += 1)
+			while (other.RelationTypeIndices.Count >= storages.Length)
+			{
+				Array.Resize(ref storages, storages.Length * 2);
+			}
+
+			while (other.RelationTypeIndices.Count >= other.storages.Length)
+			{
+				Array.Resize(ref other.storages, other.storages.Length * 2);
+			}
+
+			for (var i = 0; i < other.RelationTypeIndices.Count; i += 1)
 			{
 				if (storages[i] == null && other.storages[i] != null)
 				{

src/Snapshot.cs

@@ -1,122 +0,0 @@
-using System;
-using System.Collections.Generic;
-
-namespace MoonTools.ECS
-{
-	public class Snapshot
-	{
-		private World World;
-		private Filter? Filter;
-
-		private EntityStorage SnapshotEntityStorage;
-		private ComponentDepot SnapshotComponentDepot;
-		private RelationDepot SnapshotRelationDepot;
-
-		private List<int> SnapshotToWorldID = new List<int>();
-		private Dictionary<int, int> WorldToSnapshotID = new Dictionary<int, int>();
-
-		internal Snapshot(World world)
-		{
-			World = world;
-			SnapshotEntityStorage = new EntityStorage();
-			SnapshotComponentDepot = new ComponentDepot(World.ComponentTypeIndices);
-			SnapshotRelationDepot = new RelationDepot(World.RelationTypeIndices);
-		}
-
-		public unsafe void Take(Filter filter)
-		{
-			Clear();
-			Filter = filter;
-			SnapshotComponentDepot.CreateMissingStorages(World.ComponentDepot);
-			SnapshotRelationDepot.CreateMissingStorages(World.RelationDepot);
-
-			foreach (var worldEntity in filter.Entities)
-			{
-				var snapshotEntity = SnapshotEntityStorage.Create();
-				WorldToSnapshotID.Add(worldEntity.ID, snapshotEntity.ID);
-
-				foreach (var componentTypeIndex in World.EntityStorage.ComponentTypeIndices(worldEntity.ID))
-				{
-					SnapshotEntityStorage.SetComponent(snapshotEntity.ID, componentTypeIndex);
-					SnapshotComponentDepot.Set(snapshotEntity.ID, componentTypeIndex, World.ComponentDepot.UntypedGet(worldEntity.ID, componentTypeIndex));
-				}
-			}
-
-			foreach (var worldEntity in filter.Entities)
-			{
-				var snapshotEntityID = WorldToSnapshotID[worldEntity.ID];
-
-				foreach (var relationTypeIndex in World.EntityStorage.RelationTypeIndices(worldEntity.ID))
-				{
-					SnapshotEntityStorage.AddRelationKind(snapshotEntityID, relationTypeIndex);
-
-					foreach (var otherEntityID in World.RelationDepot.OutRelations(worldEntity.ID, relationTypeIndex))
-					{
-#if DEBUG
-						if (!World.FilterStorage.CheckSatisfied(otherEntityID, Filter.Signature))
-						{
-							throw new InvalidOperationException($"Snapshot entity {worldEntity.ID} is related to non-snapshot entity {otherEntityID}!");
-						}
-#endif
-						var relationStorageIndex = World.RelationDepot.GetStorageIndex(relationTypeIndex, worldEntity, otherEntityID);
-						var otherSnapshotID = WorldToSnapshotID[otherEntityID];
-						SnapshotEntityStorage.AddRelationKind(otherSnapshotID, relationTypeIndex);
-						SnapshotRelationDepot.Set(snapshotEntityID, otherSnapshotID, relationTypeIndex, World.RelationDepot.Get(relationTypeIndex, relationStorageIndex));
-					}
-				}
-			}
-		}
-
-		public unsafe void Restore()
-		{
-			if (Filter == null)
-			{
-				return;
-			}
-
-			foreach (var entity in Filter.Entities)
-			{
-				World.Destroy(entity);
-			}
-
-			for (var i = 0; i < SnapshotEntityStorage.Count; i += 1)
-			{
-				var entity = World.CreateEntity();
-				SnapshotToWorldID.Add(entity.ID);
-
-				foreach (var componentTypeIndex in SnapshotEntityStorage.ComponentTypeIndices(i))
-				{
-					World.EntityStorage.SetComponent(entity.ID, componentTypeIndex);
-					World.FilterStorage.Check(entity.ID, componentTypeIndex);
-					World.ComponentDepot.Set(entity.ID, componentTypeIndex, SnapshotComponentDepot.UntypedGet(i, componentTypeIndex));
-				}
-			}
-
-			for (var i = 0; i < SnapshotEntityStorage.Count; i += 1)
-			{
-				var worldID = SnapshotToWorldID[i];
-
-				foreach (var relationTypeIndex in SnapshotEntityStorage.RelationTypeIndices(i))
-				{
-					World.EntityStorage.AddRelationKind(worldID, relationTypeIndex);
-
-					foreach (var otherEntityID in SnapshotRelationDepot.OutRelations(i, relationTypeIndex))
-					{
-						var relationStorageIndex = SnapshotRelationDepot.GetStorageIndex(relationTypeIndex, i, otherEntityID);
-						var otherEntityWorldID = SnapshotToWorldID[otherEntityID];
-						World.RelationDepot.Set(worldID, otherEntityWorldID, relationTypeIndex, SnapshotRelationDepot.Get(relationTypeIndex, relationStorageIndex));
-					}
-				}
-			}
-		}
-
-		private void Clear()
-		{
-			SnapshotEntityStorage.Clear();
-			SnapshotComponentDepot.Clear();
-			SnapshotRelationDepot.Clear();
-			SnapshotToWorldID.Clear();
-			WorldToSnapshotID.Clear();
-		}
-	}
-}

src/World.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 
 namespace MoonTools.ECS
 {
@@ -23,9 +24,19 @@ namespace MoonTools.ECS
 			TemplateComponentDepot = new ComponentDepot(ComponentTypeIndices);
 		}
 
-		public Entity CreateEntity()
+		public Entity CreateEntity(string tag = "")
 		{
-			return EntityStorage.Create();
+			return EntityStorage.Create(tag);
+		}
+
+		public void Tag(Entity entity, string tag)
+		{
+			EntityStorage.Tag(entity, tag);
+		}
+
+		public string GetTag(Entity entity)
+		{
+			return EntityStorage.Tag(entity);
 		}
 
 		public void Set<TComponent>(Entity entity, in TComponent component) where TComponent : unmanaged
@@ -45,6 +56,17 @@ namespace MoonTools.ECS
 			}
 		}
 
+		// untyped version for Transfer
+		internal unsafe void Set(Entity entity, int componentTypeIndex, void* component)
+		{
+			ComponentDepot.Set(entity.ID, componentTypeIndex, component);
+
+			if (EntityStorage.SetComponent(entity.ID, componentTypeIndex))
+			{
+				FilterStorage.Check(entity.ID, componentTypeIndex);
+			}
+		}
+
 		public void Remove<TComponent>(in Entity entity) where TComponent : unmanaged
 		{
 			if (EntityStorage.RemoveComponent(entity.ID, ComponentTypeIndices.GetIndex<TComponent>()))
@@ -63,6 +85,14 @@ namespace MoonTools.ECS
 			EntityStorage.AddRelationKind(entityB.ID, relationTypeIndex);
 		}
 
+		// untyped version for Transfer
+		internal unsafe void Relate(Entity entityA, Entity entityB, int relationTypeIndex, void* relationData)
+		{
+			RelationDepot.Set(entityA, entityB, relationTypeIndex, relationData);
+			EntityStorage.AddRelationKind(entityA.ID, relationTypeIndex);
+			EntityStorage.AddRelationKind(entityB.ID, relationTypeIndex);
+		}
+
 		public void Unrelate<TRelationKind>(in Entity entityA, in Entity entityB) where TRelationKind : unmanaged
 		{
 			var (aEmpty, bEmpty) = RelationDepot.Remove<TRelationKind>(entityA, entityB);
@@ -118,9 +148,65 @@ namespace MoonTools.ECS
 			MessageDepot.Clear();
 		}
 
-		public Snapshot CreateSnapshot()
+		private Dictionary<int, int> WorldToTransferID = new Dictionary<int, int>();
+
+		// FIXME: this API sucks
+		public unsafe void Transfer(World other, Filter filter, Filter otherFilter)
 		{
-			return new Snapshot(this);
+			WorldToTransferID.Clear();
+			other.ComponentDepot.CreateMissingStorages(ComponentDepot);
+			other.RelationDepot.CreateMissingStorages(RelationDepot);
+
+			// destroy all entities matching the filter
+			foreach (var entity in otherFilter.Entities)
+			{
+				other.Destroy(entity);
+			}
+
+			// create entities and set their components
+			foreach (var entity in filter.Entities)
+			{
+				TransferEntity(other, entity);
+			}
+
+			// set relations
+			// FIXME: something is going wrong here, the transfer back isn't working
+			foreach (var entity in filter.Entities)
+			{
+				var otherWorldEntityA = WorldToTransferID[entity.ID];
+
+				foreach (var relationTypeIndex in EntityStorage.RelationTypeIndices(entity.ID))
+				{
+					foreach (var entityB in RelationDepot.OutRelations(entity.ID, relationTypeIndex))
+					{
+						var storageIndex = RelationDepot.GetStorageIndex(relationTypeIndex, entity.ID, entityB);
+
+						int otherWorldEntityB;
+						if (WorldToTransferID.TryGetValue(entityB, out otherWorldEntityB))
+						{
+							other.Relate(otherWorldEntityA, otherWorldEntityB, relationTypeIndex, RelationDepot.Get(relationTypeIndex, storageIndex));
+						}
+						else
+						{
+							// related entity is not in the filter
+							throw new Exception($"Missing transfer entity! {EntityStorage.Tag(entity.ID)} related to {EntityStorage.Tag(entityB.ID)}");
+						}
+					}
+				}
+			}
+		}
+
+		private unsafe int TransferEntity(World other, Entity entity)
+		{
+			var otherWorldEntity = other.CreateEntity(GetTag(entity));
+			WorldToTransferID.Add(entity.ID, otherWorldEntity.ID);
+
+			foreach (var componentTypeIndex in EntityStorage.ComponentTypeIndices(entity.ID))
+			{
+				other.Set(otherWorldEntity, componentTypeIndex, ComponentDepot.UntypedGet(entity.ID, componentTypeIndex));
+			}
+
+			return otherWorldEntity.ID;
 		}
 	}
 }