snapshot system

src/Rev2/Archetype.cs

@@ -1,24 +1,38 @@
 using System.Collections.Generic;
 
-namespace MoonTools.ECS.Rev2
+namespace MoonTools.ECS.Rev2;
+
+internal class Archetype
 {
-	public class Archetype
+	public World World;
+	public ArchetypeSignature Signature;
+	public List<Column> ComponentColumns = new List<Column>();
+	public List<EntityId> RowToEntity = new List<EntityId>();
+
+	public Dictionary<ComponentId, int> ComponentToColumnIndex =
+		new Dictionary<ComponentId, int>();
+	public SortedDictionary<ComponentId, ArchetypeEdge> Edges = new SortedDictionary<ComponentId, ArchetypeEdge>();
+
+	public int Count => RowToEntity.Count;
+
+	public Archetype(World world, ArchetypeSignature signature)
 	{
-		public ArchetypeSignature Signature;
+		World = world;
-		public ArchetypeId Id { get; private set; }
+		Signature = signature;
-		public List<Column> Components = new List<Column>();
+	}
-		public List<EntityId> RowToEntity = new List<EntityId>();
 
-		public Dictionary<ComponentId, int> ComponentToColumnIndex =
+	public void ClearAll()
-			new Dictionary<ComponentId, int>();
+	{
-		public SortedDictionary<ComponentId, ArchetypeEdge> Edges = new SortedDictionary<ComponentId, ArchetypeEdge>();
+		for (int i = 0; i < ComponentColumns.Count; i += 1)
-
-		public int Count => RowToEntity.Count;
-
-		public Archetype(ArchetypeId id, ArchetypeSignature signature)
 		{
-			Id = id;
+			ComponentColumns[i].Count = 0;
-			Signature = signature;
 		}
+
+		foreach (var entityId in RowToEntity)
+		{
+			World.FreeEntity(entityId);
+		}
+
+		RowToEntity.Clear();
 	}
 }

src/Rev2/ArchetypeEdge.cs

@@ -1,4 +1,4 @@
 namespace MoonTools.ECS.Rev2
 {
-	public readonly record struct ArchetypeEdge(Archetype Add, Archetype Remove);
+	internal readonly record struct ArchetypeEdge(Archetype Add, Archetype Remove);
 }

src/Rev2/ArchetypeId.cs

@@ -1,4 +0,0 @@
-namespace MoonTools.ECS.Rev2
-{
-	public readonly record struct ArchetypeId(int Id) : IHasId;
-}

src/Rev2/ArchetypeSignature.cs

@@ -3,7 +3,7 @@ using System.Collections.Generic;
 
 namespace MoonTools.ECS.Rev2
 {
-	public class ArchetypeSignature : IEquatable<ArchetypeSignature>
+	internal class ArchetypeSignature : IEquatable<ArchetypeSignature>
 	{
 		public static ArchetypeSignature Empty = new ArchetypeSignature(0);
 

src/Rev2/Column.cs

@@ -3,12 +3,13 @@ using System.Runtime.InteropServices;
 
 namespace MoonTools.ECS.Rev2
 {
-	public unsafe class Column : IDisposable
+	internal unsafe class Column : IDisposable
 	{
 		public nint Elements;
-		public int ElementSize;
 		public int Count;
-		public int Capacity;
+
+		private int Capacity;
+		private readonly int ElementSize;
 
 		private bool IsDisposed;
 
@@ -27,6 +28,12 @@ namespace MoonTools.ECS.Rev2
 			Elements = (nint) NativeMemory.Realloc((void*) Elements, (nuint) (ElementSize * Capacity));
 		}
 
+		private void ResizeTo(int capacity)
+		{
+			Capacity = capacity;
+			Elements = (nint) NativeMemory.Realloc((void*) Elements, (nuint) (ElementSize * Capacity));
+		}
+
 		// Fills gap by copying final element to the deleted index
 		public void Delete(int index)
 		{
@@ -53,7 +60,7 @@ namespace MoonTools.ECS.Rev2
 			Count += 1;
 		}
 
-		public void CopyToEnd(int index, Column other)
+		public void CopyElementToEnd(int index, Column other)
 		{
 			if (other.Count >= other.Capacity)
 			{
@@ -69,6 +76,22 @@ namespace MoonTools.ECS.Rev2
 			other.Count += 1;
 		}
 
+		public void CopyAllTo(Column other)
+		{
+			if (Count >= other.Capacity)
+			{
+				other.ResizeTo(Count);
+			}
+
+			NativeMemory.Copy(
+				(void*) Elements,
+				(void*) other.Elements,
+				(nuint) (ElementSize * Count)
+			);
+
+			other.Count = Count;
+		}
+
 		protected virtual void Dispose(bool disposing)
 		{
 			if (!IsDisposed)

src/Rev2/ComponentId.cs

@@ -2,7 +2,7 @@ using System;
 
 namespace MoonTools.ECS.Rev2
 {
-	public readonly record struct ComponentId(int Id) : IHasId, IComparable<ComponentId>
+	internal readonly record struct ComponentId(int Id) : IHasId, IComparable<ComponentId>
 	{
 		public int CompareTo(ComponentId other)
 		{

src/Rev2/Filter.cs

@@ -47,6 +47,15 @@ namespace MoonTools.ECS.Rev2
 			}
 		}
 
+		public EntityId RandomEntity
+		{
+			get
+			{
+				var randomIndex = RandomManager.Next(Count);
+				return NthEntity(randomIndex);
+			}
+		}
+
 		// WARNING: this WILL crash if the index is out of range!
 		public EntityId NthEntity(int index)
 		{
@@ -66,16 +75,25 @@ namespace MoonTools.ECS.Rev2
 			throw new InvalidOperationException("Filter index out of range!");
 		}
 
-		public EntityId RandomEntity
+		public void DestroyAllEntities()
 		{
-			get
+			foreach (var archetype in Archetypes)
 			{
-				var randomIndex = RandomManager.Next(Count);
+				archetype.ClearAll();
-				return NthEntity(randomIndex);
 			}
 		}
 
-		public Filter(Archetype emptyArchetype, HashSet<ComponentId> included, HashSet<ComponentId> excluded)
+		public void TakeSnapshot(Snapshot snapshot)
+		{
+			snapshot.Reset();
+
+			foreach (var archetype in Archetypes)
+			{
+				snapshot.TakeArchetypeSnapshot(archetype);
+			}
+		}
+
+		internal Filter(Archetype emptyArchetype, HashSet<ComponentId> included, HashSet<ComponentId> excluded)
 		{
 			EmptyArchetype = emptyArchetype;
 			Included = included;
@@ -85,7 +103,6 @@ namespace MoonTools.ECS.Rev2
 		internal ref struct ArchetypeEnumerator
 		{
 			private Archetype CurrentArchetype;
-			private bool Active;
 
 			// TODO: pool these
 			private Queue<Archetype> ArchetypeQueue = new Queue<Archetype>();
@@ -96,8 +113,6 @@ namespace MoonTools.ECS.Rev2
 
 			public ArchetypeEnumerator(Filter filter)
 			{
-				Active = false;
-
 				var empty = filter.EmptyArchetype;
 				ArchetypeSearchQueue.Enqueue(empty);
 
@@ -127,27 +142,14 @@ namespace MoonTools.ECS.Rev2
 						ArchetypeQueue.Enqueue(current);
 					}
 
-					// if the current archetype satisfies the filter, we need to add all edges that
+					// breadth-first search
-					// do not have an excluded component
+					// ignore excluded component edges
-					// if the current archetype does not satisfy the filter, we need to add all edges that
-					// include an included component
 					foreach (var (componentId, edge) in current.Edges)
 					{
-						if (satisfiesFilter)
+						if (!Explored.Contains(edge.Add) && !filter.Excluded.Contains(componentId))
 						{
-							if (!filter.Excluded.Contains(componentId) && !Explored.Contains(edge.Add))
+							Explored.Add(edge.Add);
-							{
+							ArchetypeSearchQueue.Enqueue(edge.Add);
-								Explored.Add(edge.Add);
-								ArchetypeSearchQueue.Enqueue(edge.Add);
-							}
-						}
-						else
-						{
-							if (filter.Included.Contains(componentId) && !Explored.Contains(edge.Add))
-							{
-								Explored.Add(edge.Add);
-								ArchetypeSearchQueue.Enqueue(edge.Add);
-							}
 						}
 					}
 				}

src/Rev2/FilterBuilder.cs

@@ -0,0 +1,42 @@
+using System.Collections.Generic;
+
+namespace MoonTools.ECS.Rev2
+{
+	public ref struct FilterBuilder
+	{
+		World World;
+		HashSet<ComponentId> Included;
+		HashSet<ComponentId> Excluded;
+
+		internal FilterBuilder(World world)
+		{
+			World = world;
+			Included = new HashSet<ComponentId>();
+			Excluded = new HashSet<ComponentId>();
+		}
+
+		private FilterBuilder(World world, HashSet<ComponentId> included, HashSet<ComponentId> excluded)
+		{
+			World = world;
+			Included = included;
+			Excluded = excluded;
+		}
+
+		public FilterBuilder Include<T>() where T : unmanaged
+		{
+			Included.Add(World.TypeToComponentId[typeof(T)]);
+			return new FilterBuilder(World, Included, Excluded);
+		}
+
+		public FilterBuilder Exclude<T>() where T : unmanaged
+		{
+			Excluded.Add(World.TypeToComponentId[typeof(T)]);
+			return new FilterBuilder(World, Included, Excluded);
+		}
+
+		public Filter Build()
+		{
+			return new Filter(World.EmptyArchetype, Included, Excluded);
+		}
+	}
+}

src/Rev2/IdAssigner.cs

@@ -2,7 +2,7 @@ using System.Collections.Generic;
 
 namespace MoonTools.ECS.Rev2
 {
-	public class IdAssigner<T> where T : struct, IHasId
+	internal class IdAssigner<T> where T : struct, IHasId
 	{
 		int Next;
 		Queue<int> AvailableIds = new Queue<int>();

src/Rev2/Record.cs

@@ -1,4 +1,4 @@
 namespace MoonTools.ECS.Rev2
 {
-	public readonly record struct Record(Archetype Archetype, int Row);
+	internal readonly record struct Record(Archetype Archetype, int Row);
 }

src/Rev2/Snapshot.cs

@@ -0,0 +1,110 @@
+using System.Collections.Generic;
+
+namespace MoonTools.ECS.Rev2;
+
+public class Snapshot
+{
+	private Dictionary<ArchetypeSignature, ArchetypeSnapshot> ArchetypeSnapshots =
+		new Dictionary<ArchetypeSignature, ArchetypeSnapshot>();
+
+	public int Count
+	{
+		get
+		{
+			var count = 0;
+
+			foreach (var snapshot in ArchetypeSnapshots.Values)
+			{
+				count += snapshot.Count;
+			}
+
+			return count;
+		}
+	}
+
+	public void Restore(World world)
+	{
+		foreach (var (archetypeSignature, archetypeSnapshot) in ArchetypeSnapshots)
+		{
+			var archetype = world.ArchetypeIndex[archetypeSignature];
+			RestoreArchetypeSnapshot(archetype);
+		}
+	}
+
+	internal void Reset()
+	{
+		foreach (var archetypeSnapshot in ArchetypeSnapshots.Values)
+		{
+			archetypeSnapshot.Count = 0;
+		}
+	}
+
+	internal void TakeArchetypeSnapshot(Archetype archetype)
+	{
+		if (!ArchetypeSnapshots.TryGetValue(archetype.Signature, out var archetypeSnapshot))
+		{
+			archetypeSnapshot = new ArchetypeSnapshot(archetype.Signature);
+			ArchetypeSnapshots.Add(archetype.Signature, archetypeSnapshot);
+		}
+
+		archetypeSnapshot.Take(archetype);
+	}
+
+	private void RestoreArchetypeSnapshot(Archetype archetype)
+	{
+		var archetypeSnapshot = ArchetypeSnapshots[archetype.Signature];
+		archetypeSnapshot.Restore(archetype);
+	}
+
+	private class ArchetypeSnapshot
+	{
+		public ArchetypeSignature Signature;
+		public readonly List<Column> ComponentColumns;
+
+		public int Count;
+
+		public ArchetypeSnapshot(ArchetypeSignature signature)
+		{
+			Signature = signature;
+			ComponentColumns = new List<Column>(signature.Count);
+
+			for (int i = 0; i < signature.Count; i += 1)
+			{
+				var componentId = signature[i];
+				ComponentColumns.Add(new Column(World.ElementSizes[componentId]));
+			}
+		}
+
+		public void Take(Archetype archetype)
+		{
+			for (int i = 0; i < ComponentColumns.Count; i += 1)
+			{
+				archetype.ComponentColumns[i].CopyAllTo(ComponentColumns[i]);
+			}
+
+			Count = archetype.Count;
+		}
+
+		public void Restore(Archetype archetype)
+		{
+			// Clear out existing entities
+			archetype.ClearAll();
+
+			// Copy all component data
+			for (int i = 0; i < ComponentColumns.Count; i += 1)
+			{
+				ComponentColumns[i].CopyAllTo(archetype.ComponentColumns[i]);
+			}
+
+			// Clear the row to entity list
+			archetype.RowToEntity.Clear();
+
+			// Create new entities and repopulate the row to entity list
+			for (int i = 0; i < Count; i += 1)
+			{
+				var entityId = archetype.World.CreateEntityOnArchetype(archetype);
+				archetype.RowToEntity.Add(entityId);
+			}
+		}
+	}
+}

src/Rev2/World.cs

@@ -7,8 +7,13 @@ namespace MoonTools.ECS.Rev2
 {
 	public class World : IDisposable
 	{
+		// Get ComponentId from a Type
+		internal static Dictionary<Type, ComponentId> TypeToComponentId = new Dictionary<Type, ComponentId>();
+		// Get element size from a ComponentId
+		internal static Dictionary<ComponentId, int> ElementSizes = new Dictionary<ComponentId, int>();
+
 		// Lookup from ArchetypeSignature to Archetype
-		Dictionary<ArchetypeSignature, Archetype> ArchetypeIndex = new Dictionary<ArchetypeSignature, Archetype>();
+		internal Dictionary<ArchetypeSignature, Archetype> ArchetypeIndex = new Dictionary<ArchetypeSignature, Archetype>();
 
 		// Going from EntityId to Archetype and storage row
 		Dictionary<EntityId, Record> EntityIndex = new Dictionary<EntityId, Record>();
@@ -16,18 +21,13 @@ namespace MoonTools.ECS.Rev2
 		// Going from ComponentId to Archetype list
 		Dictionary<ComponentId, List<Archetype>> ComponentIndex = new Dictionary<ComponentId, List<Archetype>>();
 
-		// Get ComponentId from a Type
-		Dictionary<Type, ComponentId> TypeToComponentId = new Dictionary<Type, ComponentId>();
-
-		// Get element size from a ComponentId
-		Dictionary<ComponentId, int> ElementSizes = new Dictionary<ComponentId, int>();
-
 		// ID Management
-		IdAssigner<ArchetypeId> ArchetypeIdAssigner = new IdAssigner<ArchetypeId>();
 		IdAssigner<EntityId> EntityIdAssigner = new IdAssigner<EntityId>();
 		IdAssigner<ComponentId> ComponentIdAssigner = new IdAssigner<ComponentId>();
 
-		public readonly Archetype EmptyArchetype;
+		internal readonly Archetype EmptyArchetype;
+
+		public FilterBuilder FilterBuilder => new FilterBuilder(this);
 
 		private bool IsDisposed;
 
@@ -39,12 +39,11 @@ namespace MoonTools.ECS.Rev2
 			EmptyArchetype = CreateArchetype(ArchetypeSignature.Empty);
 		}
 
-		private Archetype CreateArchetype(ArchetypeSignature signature)
+		internal Archetype CreateArchetype(ArchetypeSignature signature)
 		{
-			var archetypeId = ArchetypeIdAssigner.Assign();
+			var archetype = new Archetype(this, signature)
-			var archetype = new Archetype(archetypeId, signature)
 			{
-				Components = new List<Column>(signature.Count)
+				ComponentColumns = new List<Column>(signature.Count)
 			};
 
 			ArchetypeIndex.Add(signature, archetype);
@@ -52,9 +51,9 @@ namespace MoonTools.ECS.Rev2
 			for (int i = 0; i < signature.Count; i += 1)
 			{
 				var componentId = signature[i];
-				ComponentIndex[componentId].Add(archetype); //, new ArchetypeRecord(i));
+				ComponentIndex[componentId].Add(archetype);
-				archetype.ComponentToColumnIndex.Add(componentId, archetype.Components.Count);
+				archetype.ComponentToColumnIndex.Add(componentId, archetype.ComponentColumns.Count);
-				archetype.Components.Add(new Column(ElementSizes[componentId]));
+				archetype.ComponentColumns.Add(new Column(ElementSizes[componentId]));
 			}
 
 			return archetype;
@@ -63,12 +62,27 @@ namespace MoonTools.ECS.Rev2
 		public EntityId CreateEntity()
 		{
 			var entityId = EntityIdAssigner.Assign();
-			var emptyArchetype = ArchetypeIndex[ArchetypeSignature.Empty];
+			EntityIndex.Add(entityId, new Record(EmptyArchetype, EmptyArchetype.Count));
-			EntityIndex.Add(entityId, new Record(emptyArchetype, emptyArchetype.Count));
+			EmptyArchetype.RowToEntity.Add(entityId);
-			emptyArchetype.RowToEntity.Add(entityId);
 			return entityId;
 		}
 
+		// used as a fast path by Archetype.Transfer
+		internal EntityId CreateEntityOnArchetype(Archetype archetype)
+		{
+			var entityId = EntityIdAssigner.Assign();
+			EntityIndex.Add(entityId, new Record(archetype, archetype.Count));
+			archetype.RowToEntity.Add(entityId);
+			return entityId;
+		}
+
+		// used as a fast path by Archetype.ClearAll
+		internal void FreeEntity(EntityId entityId)
+		{
+			EntityIndex.Remove(entityId);
+			EntityIdAssigner.Unassign(entityId);
+		}
+
 		// FIXME: would be much more efficient to do all this at load time somehow
 		private void RegisterComponent<T>() where T : unmanaged
 		{
@@ -80,12 +94,21 @@ namespace MoonTools.ECS.Rev2
 
 		private void TryRegisterComponentId<T>() where T : unmanaged
 		{
-			if (!TypeToComponentId.TryGetValue(typeof(T), out var componentId))
+			if (!TypeToComponentId.ContainsKey(typeof(T)))
 			{
 				RegisterComponent<T>();
 			}
 		}
 
+		// non-generic variant for use with Transfer
+		internal void AddComponentIndexEntry(ComponentId componentId)
+		{
+			if (!ComponentIndex.ContainsKey(componentId))
+			{
+				ComponentIndex.Add(componentId, new List<Archetype>());
+			}
+		}
+
 		[MethodImpl(MethodImplOptions.AggressiveInlining)]
 		private ComponentId GetComponentId<T>() where T : unmanaged
 		{
@@ -106,7 +129,7 @@ namespace MoonTools.ECS.Rev2
 
 			var record = EntityIndex[entityId];
 			var columnIndex = record.Archetype.ComponentToColumnIndex[componentId];
-			var column = record.Archetype.Components[columnIndex];
+			var column = record.Archetype.ComponentColumns[columnIndex];
 
 			return ref ((T*) column.Elements)[record.Row];
 		}
@@ -120,7 +143,7 @@ namespace MoonTools.ECS.Rev2
 			{
 				var record = EntityIndex[entityId];
 				var columnIndex = record.Archetype.ComponentToColumnIndex[componentId];
-				var column = record.Archetype.Components[columnIndex];
+				var column = record.Archetype.ComponentColumns[columnIndex];
 
 				((T*) column.Elements)[record.Row] = component;
 			}
@@ -165,7 +188,7 @@ namespace MoonTools.ECS.Rev2
 
 			// add the new component to the new archetype
 			var columnIndex = nextArchetype.ComponentToColumnIndex[componentId];
-			var column = nextArchetype.Components[columnIndex];
+			var column = nextArchetype.ComponentColumns[columnIndex];
 			column.Append(component);
 		}
 
@@ -207,9 +230,9 @@ namespace MoonTools.ECS.Rev2
 			var archetype = record.Archetype;
 			var row = record.Row;
 
-			for (int i = 0; i < archetype.Components.Count; i += 1)
+			for (int i = 0; i < archetype.ComponentColumns.Count; i += 1)
 			{
-				archetype.Components[i].Delete(row);
+				archetype.ComponentColumns[i].Delete(row);
 			}
 
 			if (row != archetype.Count - 1)
@@ -227,16 +250,16 @@ namespace MoonTools.ECS.Rev2
 
 		private void MoveEntityToHigherArchetype(EntityId entityId, int row, Archetype from, Archetype to)
 		{
-			for (int i = 0; i < from.Components.Count; i += 1)
+			for (int i = 0; i < from.ComponentColumns.Count; i += 1)
 			{
 				var componentId = from.Signature[i];
 				var destinationColumnIndex = to.ComponentToColumnIndex[componentId];
 
 				// copy all components to higher archetype
-				from.Components[i].CopyToEnd(row, to.Components[destinationColumnIndex]);
+				from.ComponentColumns[i].CopyElementToEnd(row, to.ComponentColumns[destinationColumnIndex]);
 
 				// delete row on from archetype
-				from.Components[i].Delete(row);
+				from.ComponentColumns[i].Delete(row);
 			}
 
 			if (row != from.Count - 1)
@@ -256,18 +279,18 @@ namespace MoonTools.ECS.Rev2
 
 		private void MoveEntityToLowerArchetype(EntityId entityId, int row, Archetype from, Archetype to, ComponentId removed)
 		{
-			for (int i = 0; i < from.Components.Count; i += 1)
+			for (int i = 0; i < from.ComponentColumns.Count; i += 1)
 			{
 				var componentId = from.Signature[i];
 
 				// delete the row
-				from.Components[i].Delete(row);
+				from.ComponentColumns[i].Delete(row);
 
 				// if this isn't the removed component, copy to the lower archetype
 				if (componentId != removed)
 				{
 					var destinationColumnIndex = to.ComponentToColumnIndex[componentId];
-					from.Components[i].CopyToEnd(row, to.Components[destinationColumnIndex]);
+					from.ComponentColumns[i].CopyElementToEnd(row, to.ComponentColumns[destinationColumnIndex]);
 				}
 			}
 
@@ -293,11 +316,11 @@ namespace MoonTools.ECS.Rev2
 			{
 				var componentIdOne = archetype.Signature[0];
 				var columnIndexOne = archetype.ComponentToColumnIndex[componentIdOne];
-				var columnOneElements = archetype.Components[columnIndexOne].Elements;
+				var columnOneElements = archetype.ComponentColumns[columnIndexOne].Elements;
 
 				var componentIdTwo = archetype.Signature[1];
 				var columnIndexTwo = archetype.ComponentToColumnIndex[componentIdTwo];
-				var columnTwoElements = archetype.Components[columnIndexTwo].Elements;
+				var columnTwoElements = archetype.ComponentColumns[columnIndexTwo].Elements;
 
 				for (int i = archetype.Count - 1; i >= 0; i -= 1)
 				{
@@ -312,11 +335,11 @@ namespace MoonTools.ECS.Rev2
 			{
 				var componentIdOne = archetype.Signature[0];
 				var columnIndexOne = archetype.ComponentToColumnIndex[componentIdOne];
-				var columnOneElements = archetype.Components[columnIndexOne].Elements;
+				var columnOneElements = archetype.ComponentColumns[columnIndexOne].Elements;
 
 				var componentIdTwo = archetype.Signature[1];
 				var columnIndexTwo = archetype.ComponentToColumnIndex[componentIdTwo];
-				var columnTwoElements = archetype.Components[columnIndexTwo].Elements;
+				var columnTwoElements = archetype.ComponentColumns[columnIndexTwo].Elements;
 
 				for (int i = archetype.Count - 1; i >= 0; i -= 1)
 				{
@@ -336,7 +359,7 @@ namespace MoonTools.ECS.Rev2
 					{
 						for (var i = 0; i < archetype.Signature.Count; i += 1)
 						{
-							archetype.Components[i].Dispose();
+							archetype.ComponentColumns[i].Dispose();
 						}
 					}
 				}