Fixed an issue where Archetypes were iterated if they contained 0 e…

…ntitys.

src/Arch.Tests/EnumeratorTest.cs

@@ -7,7 +7,7 @@ namespace Arch.Tests;
 
 /// <summary>
 ///     The <see cref="EnumeratorTest"/>
-///     checks if the enumerators inside the common classes work correctly. 
+///     checks if the enumerators inside the common classes work correctly.
 /// </summary>
 [TestFixture]
 public class EnumeratorTest
@@ -37,7 +37,7 @@ public void Setup()
     }
 
     /// <summary>
-    ///     Checks if the <see cref="World"/> <see cref="World.Archetypes"/> are enumerated correctly. 
+    ///     Checks if the <see cref="World"/> <see cref="World.Archetypes"/> are enumerated correctly.
     /// </summary>
     [Test]
     public void WorldArchetypeEnumeration()
@@ -56,7 +56,7 @@ public void WorldArchetypeEnumeration()
     }
 
     /// <summary>
-    ///     Checks if the <see cref="Archetype"/> <see cref="Archetype.Chunks"/> are enumerated correctly. 
+    ///     Checks if the <see cref="Archetype"/> <see cref="Archetype.Chunks"/> are enumerated correctly.
     /// </summary>
     [Test]
     public void ArchetypeChunkEnumeration()
@@ -72,7 +72,7 @@ public void ArchetypeChunkEnumeration()
     }
 
     /// <summary>
-    ///     Checks if the <see cref="Query"/> archetypes are enumerated correctly. 
+    ///     Checks if the <see cref="Query"/> archetypes are enumerated correctly.
     /// </summary>
     [Test]
     public void QueryArchetypeEnumeration()
@@ -88,7 +88,29 @@ public void QueryArchetypeEnumeration()
     }
 
     /// <summary>
-    ///     Checks if the <see cref="Query"/> chunks are enumerated correctly. 
+    ///     Checks if the <see cref="Query"/> archetypes are enumerated correctly when theres one empty archetype.
+    ///     In the past it did not which caused weird query behaviour in certain situations where there was one empty archetype with one empty chunk.
+    /// </summary>
+    [Test]
+    public void QueryArchetypeEmptyEnumeration()
+    {
+        // Create world, entity and move it.
+        using var world = World.Create();
+        var entity = world.Create();
+        world.Add<int>(entity);
+
+        var counter = 0;
+        var query = world.Query(QueryDescription.Null);
+        foreach (var archetype in query.GetArchetypeIterator())
+        {
+            counter++;
+        }
+
+        That(counter, Is.EqualTo(1));
+    }
+
+    /// <summary>
+    ///     Checks if the <see cref="Query"/> chunks are enumerated correctly.
     /// </summary>
     [Test]
     public void QueryChunkEnumeration()

src/Arch.Tests/WorldTest.cs

@@ -277,7 +277,6 @@ public void TrimExcessEmptyArchetypes()
         That(world.Capacity, Is.EqualTo(archetype.Size * archetype.EntitiesPerChunk));
     }
 
-
     /// <summary>
     ///     Checks if the <see cref="World"/> clears itself correctly.
     /// </summary>

src/Arch/Arch.csproj

@@ -14,12 +14,13 @@
 
     <PackageId>Arch</PackageId>
     <Title>Arch</Title>
-    <Version>1.2.6.5-alpha</Version>
+    <Version>1.2.6.6-alpha</Version>
     <Authors>genaray</Authors>
     <PackageLicenseExpression>Apache-2.0</PackageLicenseExpression>
     <Description>A high performance c# net.6 and net.7 archetype based ECS ( Entity component system ).</Description>
     <PackageReleaseNotes>Added more dangerous utility methods. 
-Entity now implements IComparable&lt;Entity&gt;</PackageReleaseNotes>
+Entity now implements IComparable&lt;Entity&gt;.
+DangerousWorldExtension can now return the Slot for an entity, used for dangerous acess and serialisation. </PackageReleaseNotes>
     <PackageTags>c#;.net;.net6;.net7;ecs;game;entity;gamedev; game-development; game-engine; entity-component-system;</PackageTags>
 
     <PackageProjectUrl>https://github.com/genaray/Arch</PackageProjectUrl>

src/Arch/Core/Archetype.cs

@@ -160,9 +160,9 @@ internal Archetype(ComponentType[] types)
     ///     The component types that the <see cref="Arch.Core.Entity"/>'s stored here have.
     /// </summary>
     public ComponentType[] Types { [MethodImpl(MethodImplOptions.AggressiveInlining)] get; }
-    
+
     /// <summary>
-    ///     The lookup array used by this <see cref="Archetype"/>, is being passed to all its <see cref="Chunks"/> to save memory. 
+    ///     The lookup array used by this <see cref="Archetype"/>, is being passed to all its <see cref="Chunks"/> to save memory.
     /// </summary>
     internal int[] LookupArray
     {
@@ -233,7 +233,10 @@ internal Slot LastSlot
     public int Entities
     {
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        get => (Size * EntitiesPerChunk) - (EntitiesPerChunk - GetChunk(Size - 1).Size);
+        get;
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        private set;
     }
 
     /// <summary>
@@ -256,13 +259,15 @@ internal bool Add(Entity entity, out Slot slot)
         {
             slot.Index = lastChunk.Add(entity);
             slot.ChunkIndex = Size - 1;
+            Entities++;
 
             return false;
         }
 
         // Create new chunk
         var newChunk = new Chunk(EntitiesPerChunk, _componentIdToArrayIndex, Types);
         slot.Index = newChunk.Add(entity);
+        Entities++;
         slot.ChunkIndex = Size;
 
         // Resize chunks & map entity
@@ -286,6 +291,7 @@ internal void Remove(ref Slot slot, out int movedEntityId)
         // Move the last entity from the last chunk into the chunk to replace the removed entity directly
         ref var chunk = ref Chunks[slot.ChunkIndex];
         movedEntityId = chunk.Transfer(slot.Index, ref LastChunk);
+        Entities--;
 
         // Return to prevent that Size decreases when chunk IS not Empty and to prevent Size becoming 0 or -1.
         if (LastChunk.Size != 0 || Size <= 1)
@@ -426,6 +432,7 @@ internal ChunkRangeIterator GetRangeIterator(int to)
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public void Clear()
     {
+        Entities = 0;
         Size = 1;
         foreach (ref var chunk in this)
         {
@@ -662,6 +669,10 @@ internal static void Copy(Archetype source, Archetype destination)
 
             sourceChunkIndex++;
         }
+
+        // Increase entities by destination since those were copied, set source to zero since its now empty.
+        destination.Entities += source.Entities;
+        source.Entities = 0;
     }
 
     /// <summary>

src/Arch/Core/Enumerators.cs

@@ -129,7 +129,7 @@ public bool MoveNext()
         while (_archetypes.MoveNext())
         {
             var archetype = _archetypes.Current;
-            if (archetype.Size > 0 && _query.Valid(archetype.BitSet))
+            if (archetype.Entities > 0 && _query.Valid(archetype.BitSet))
             {
                 return true;
             }

src/Arch/Core/Extensions/Dangerous/DangerousWorldExtensions.cs

@@ -31,7 +31,7 @@ public static void EnsureCapacity(this World world, int capacity)
     {
         world.EntityInfo.EnsureCapacity(capacity);
     }
-    
+
     /// <summary>
     ///     Sets the <see cref="EntityInfo.Archetype"/> for an <see cref="Entity"/>.
     /// </summary>
@@ -62,7 +62,7 @@ public static void SetVersions(this World world, int[][] versions)
     {
         world.EntityInfo.Versions = (JaggedArray<int>)versions;
     }
-    
+
     /// <summary>
     ///     Returns the <see cref="EntityInfoStorage.Slots"/> of a <see cref="World"/> for reading or modifiyng it.
     /// </summary>
@@ -73,7 +73,7 @@ public static (int,int)[][] GetSlots(this World world)
         var array = (Slot[][])world.EntityInfo.Slots;
         return Unsafe.As<(int,int)[][]>(array);
     }
-    
+
     /// <summary>
     ///     Sets the <see cref="EntityInfoStorage.Slots"/> of a <see cref="World"/>.
     /// </summary>
@@ -83,7 +83,19 @@ public static void SetSlots(this World world, (int,int)[][] slots)
     {
         world.EntityInfo.Slots = (JaggedArray<Slot>) Unsafe.As<Slot[][]>(slots);
     }
-
+
+    /// <summary>
+    ///     Returns the <see cref="Slot"/> of an <see cref="Entity"/>.
+    /// </summary>
+    /// <param name="world">The <see cref="World"/>.</param>
+    /// <param name="entity">The <see cref="Entity"/>.</param>
+    /// <returns>The <see cref="Slot"/> as a <see cref="ValueTuple{T,TT}"/>.</returns>
+    public static (int, int) GetSlot(this World world, Entity entity)
+    {
+        ref var slot = ref world.EntityInfo.GetSlot(entity.Id);
+        return (slot.Index, slot.ChunkIndex);
+    }
+
     /// <summary>
     ///     Returns the <see cref="EntityInfoStorage.Archetypes"/> of a <see cref="World"/> for reading or modifiyng it.
     /// </summary>
@@ -93,7 +105,7 @@ public static Archetype[][] GetArchetypes(this World world)
     {
         return (Archetype[][])world.EntityInfo.Archetypes;
     }
-    
+
     /// <summary>
     ///     Sets the <see cref="EntityInfoStorage.Archetypes"/> of a <see cref="World"/>.
     /// </summary>

src/Arch/Core/Query.cs

@@ -13,6 +13,11 @@ namespace Arch.Core;
 public partial struct QueryDescription : IEquatable<QueryDescription>
 {
 
+    /// <summary>
+    ///     A null reference, basically an empty <see cref="QueryDescription"/> that queries for all <see cref="Entity"/>s.
+    /// </summary>
+    public static readonly QueryDescription Null = new();
+
     /// <summary>
     ///     An array of all components that an <see cref="Entity"/> should have mandatory.
     /// </summary>