+ plugins project

19 files changed, 906 insertions, 0 deletions

diff --git a/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/Aspect.cs b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/Aspect.cs
new file mode 100644
index 0000000..e6fb606
--- /dev/null
+++ b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/Aspect.cs
@@ -0,0 +1,48 @@
+using System;
+using System.Collections.Specialized;
+
+namespace MonoGame.Extended.Entities
+{
+    public class Aspect
+    {
+        internal Aspect()
+        {
+            AllSet = new BitVector32();
+            ExclusionSet = new BitVector32();
+            OneSet = new BitVector32();
+        }
+
+        public BitVector32 AllSet;
+        public BitVector32 ExclusionSet;
+        public BitVector32 OneSet;
+
+        public static AspectBuilder All(params Type[] types)
+        {
+            return new AspectBuilder().All(types);
+        }
+
+        public static AspectBuilder One(params Type[] types)
+        {
+            return new AspectBuilder().One(types);
+        }
+
+        public static AspectBuilder Exclude(params Type[] types)
+        {
+            return new AspectBuilder().Exclude(types);
+        }
+
+        public bool IsInterested(BitVector32 componentBits)
+        {
+            if (AllSet.Data != 0 && (componentBits.Data & AllSet.Data) != AllSet.Data)
+                return false;
+
+            if (ExclusionSet.Data != 0 && (componentBits.Data & ExclusionSet.Data) != 0)
+                return false;
+
+            if (OneSet.Data != 0 && (componentBits.Data & OneSet.Data) == 0)
+                return false;
+
+            return true;
+        }
+    }
+}
\ No newline at end of file
diff --git a/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/AspectBuilder.cs b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/AspectBuilder.cs
new file mode 100644
index 0000000..d749795
--- /dev/null
+++ b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/AspectBuilder.cs
@@ -0,0 +1,63 @@
+using System;
+using System.Collections.Specialized;
+using MonoGame.Extended.Collections;
+
+namespace MonoGame.Extended.Entities
+{
+    public class AspectBuilder
+    {
+        public AspectBuilder()
+        {
+            AllTypes = new Bag<Type>();
+            ExclusionTypes = new Bag<Type>();
+            OneTypes = new Bag<Type>();
+        }
+
+        public Bag<Type> AllTypes { get; }
+        public Bag<Type> ExclusionTypes { get; }
+        public Bag<Type> OneTypes { get; }
+
+        public AspectBuilder All(params Type[] types)
+        {
+            foreach (var type in types)
+                AllTypes.Add(type);
+
+            return this;
+        }
+
+        public AspectBuilder One(params Type[] types)
+        {
+            foreach (var type in types)
+                OneTypes.Add(type);
+
+            return this;
+        }
+
+        public AspectBuilder Exclude(params Type[] types)
+        {
+            foreach (var type in types)
+                ExclusionTypes.Add(type);
+
+            return this;
+        }
+
+        public Aspect Build(ComponentManager componentManager)
+        {
+            var aspect = new Aspect();
+            Associate(componentManager, AllTypes, ref aspect.AllSet);
+            Associate(componentManager, OneTypes, ref aspect.OneSet);
+            Associate(componentManager, ExclusionTypes, ref aspect.ExclusionSet);
+            return aspect;
+        }
+
+        // ReSharper disable once ParameterTypeCanBeEnumerable.Local
+        private static void Associate(ComponentManager componentManager, Bag<Type> types, ref BitVector32 bits)
+        {
+            foreach (var type in types)
+            {
+                var id = componentManager.GetComponentTypeId(type);
+                bits[1 << id] = true;
+            }
+        }
+    }
+}
\ No newline at end of file
diff --git a/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/BitArrayExtensions.cs b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/BitArrayExtensions.cs
new file mode 100644
index 0000000..2ca0737
--- /dev/null
+++ b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/BitArrayExtensions.cs
@@ -0,0 +1,54 @@
+using System;
+using System.Collections;
+
+namespace MonoGame.Extended.Entities
+{
+    public static class BitArrayExtensions
+    {
+        public static bool IsEmpty(this BitArray bitArray)
+        {
+            for (var i = 0; i < bitArray.Length; i++)
+            {
+                if (bitArray[i])
+                    return false;
+            }
+
+            return true;
+        }
+
+        public static bool ContainsAll(this BitArray bitArray, BitArray other)
+        {
+            var otherBitsLength = other.Length;
+            var bitsLength = bitArray.Length;
+
+            for (var i = bitsLength; i < otherBitsLength; i++)
+            {
+                if (other[i])
+                    return false;
+            }
+
+            var s = Math.Min(bitsLength, otherBitsLength);
+
+            for (var i = 0; s > i; i++)
+            {
+                if ((bitArray[i] & other[i]) != other[i])
+                    return false;
+            }
+
+            return true;
+        }
+
+        public static bool Intersects(this BitArray bitArray, BitArray other)
+        {
+            var s = Math.Min(bitArray.Length, other.Length);
+
+            for (var i = 0; s > i; i++)
+            {
+                if (bitArray[i] & other[i])
+                    return true;
+            }
+
+            return false;
+        }
+    }
+}
\ No newline at end of file
diff --git a/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/ComponentManager.cs b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/ComponentManager.cs
new file mode 100644
index 0000000..a59c87c
--- /dev/null
+++ b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/ComponentManager.cs
@@ -0,0 +1,90 @@
+using System;
+using System.Collections.Generic;
+using System.Collections.Specialized;
+using Microsoft.Xna.Framework;
+using MonoGame.Extended.Collections;
+using MonoGame.Extended.Entities.Systems;
+
+namespace MonoGame.Extended.Entities
+{
+    public interface IComponentMapperService
+    {
+        ComponentMapper<T> GetMapper<T>() where T : class;
+    }
+
+    public class ComponentManager : UpdateSystem, IComponentMapperService
+    {
+        public ComponentManager()
+        {
+            _componentMappers = new Bag<ComponentMapper>();
+            _componentTypes = new Dictionary<Type, int>();
+        }
+
+        private readonly Bag<ComponentMapper> _componentMappers;
+        private readonly Dictionary<Type, int> _componentTypes;
+
+        public Action<int> ComponentsChanged;
+
+        private ComponentMapper<T> CreateMapperForType<T>(int componentTypeId)
+            where T : class
+        {
+            // TODO: We can probably do better than this without a huge performance penalty by creating our own bit vector that grows after the first 32 bits.
+            if (componentTypeId >= 32)
+                throw new InvalidOperationException("Component type limit exceeded. We currently only allow 32 component types for performance reasons.");
+
+            var mapper = new ComponentMapper<T>(componentTypeId, ComponentsChanged);
+            _componentMappers[componentTypeId] = mapper;
+            return mapper;
+        }
+
+        public ComponentMapper GetMapper(int componentTypeId)
+        {
+            return _componentMappers[componentTypeId];
+        }
+
+        public ComponentMapper<T> GetMapper<T>()
+            where T : class
+        {
+            var componentTypeId = GetComponentTypeId(typeof(T));
+
+            if (_componentMappers[componentTypeId] != null)
+                return _componentMappers[componentTypeId] as ComponentMapper<T>;
+
+            return CreateMapperForType<T>(componentTypeId);
+        }
+
+        public int GetComponentTypeId(Type type)
+        {
+            if (_componentTypes.TryGetValue(type, out var id))
+                return id;
+
+            id = _componentTypes.Count;
+            _componentTypes.Add(type, id);
+            return id;
+        }
+
+        public BitVector32 CreateComponentBits(int entityId)
+        {
+            var componentBits = new BitVector32();
+            var mask = BitVector32.CreateMask();
+
+            for (var componentId = 0; componentId < _componentMappers.Count; componentId++)
+            {
+                componentBits[mask] = _componentMappers[componentId]?.Has(entityId) ?? false;
+                mask = BitVector32.CreateMask(mask);
+            }
+
+            return componentBits;
+        }
+
+        public void Destroy(int entityId)
+        {
+            foreach (var componentMapper in _componentMappers)
+                componentMapper?.Delete(entityId);
+        }
+
+        public override void Update(GameTime gameTime)
+        {
+        }
+    }
+}
diff --git a/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/ComponentMapper.cs b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/ComponentMapper.cs
new file mode 100644
index 0000000..35b196c
--- /dev/null
+++ b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/ComponentMapper.cs
@@ -0,0 +1,69 @@
+using System;
+using MonoGame.Extended.Collections;
+
+namespace MonoGame.Extended.Entities
+{
+    public abstract class ComponentMapper
+    {
+        protected ComponentMapper(int id, Type componentType)
+        {
+            Id = id;
+            ComponentType = componentType;
+        }
+
+        public int Id { get; }
+        public Type ComponentType { get; }
+        public abstract bool Has(int entityId);
+        public abstract void Delete(int entityId);
+    }
+
+    public class ComponentMapper<T> : ComponentMapper
+        where T : class
+    {
+        public event Action<int> OnPut;
+        public event Action<int> OnDelete;
+
+        private readonly Action<int> _onCompositionChanged;
+
+        public ComponentMapper(int id, Action<int> onCompositionChanged)
+            : base(id, typeof(T))
+        {
+            _onCompositionChanged = onCompositionChanged;
+            Components = new Bag<T>();
+        }
+
+        public Bag<T> Components { get; }
+
+        public void Put(int entityId, T component)
+        {
+            Components[entityId] = component;
+            _onCompositionChanged(entityId);
+            OnPut?.Invoke(entityId);
+        }
+
+        public T Get(Entity entity)
+        {
+            return Get(entity.Id);
+        }
+
+        public T Get(int entityId)
+        {
+            return Components[entityId];
+        }
+
+        public override bool Has(int entityId)
+        {
+            if (entityId >= Components.Count)
+                return false;
+
+            return Components[entityId] != null;
+        }
+
+        public override void Delete(int entityId)
+        {
+            Components[entityId] = null;
+            _onCompositionChanged(entityId);
+            OnDelete?.Invoke(entityId);
+        }
+    }
+}
diff --git a/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/ComponentType.cs b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/ComponentType.cs
new file mode 100644
index 0000000..ebef996
--- /dev/null
+++ b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/ComponentType.cs
@@ -0,0 +1,46 @@
+using System;
+
+namespace MonoGame.Extended.Entities
+{
+    //public class ComponentType : IEquatable<ComponentType>
+    //{
+    //    public ComponentType(Type type, int id)
+    //    {
+    //        Type = type;
+    //        Id = id;
+    //    }
+
+    //    public Type Type { get; }
+    //    public int Id { get; }
+
+    //    public bool Equals(ComponentType other)
+    //    {
+    //        if (ReferenceEquals(null, other)) return false;
+    //        if (ReferenceEquals(this, other)) return true;
+    //        return Id == other.Id;
+    //    }
+
+    //    public override bool Equals(object obj)
+    //    {
+    //        if (ReferenceEquals(null, obj)) return false;
+    //        if (ReferenceEquals(this, obj)) return true;
+    //        if (obj.GetType() != GetType()) return false;
+    //        return Equals((ComponentType) obj);
+    //    }
+
+    //    public override int GetHashCode()
+    //    {
+    //        return Id;
+    //    }
+
+    //    public static bool operator ==(ComponentType left, ComponentType right)
+    //    {
+    //        return Equals(left, right);
+    //    }
+
+    //    public static bool operator !=(ComponentType left, ComponentType right)
+    //    {
+    //        return !Equals(left, right);
+    //    }
+    //}
+}
diff --git a/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/Entity.cs b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/Entity.cs
new file mode 100644
index 0000000..a56ccff
--- /dev/null
+++ b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/Entity.cs
@@ -0,0 +1,87 @@
+using System;
+using System.Collections.Specialized;
+
+namespace MonoGame.Extended.Entities
+{
+    public class Entity : IEquatable<Entity>
+    {
+        private readonly EntityManager _entityManager;
+        private readonly ComponentManager _componentManager;
+
+        internal Entity(int id, EntityManager entityManager, ComponentManager componentManager)
+        {
+            Id = id;
+
+            _entityManager = entityManager;
+            _componentManager = componentManager;
+        }
+
+        public int Id { get; }
+        
+        public BitVector32 ComponentBits => _entityManager.GetComponentBits(Id);
+
+        public void Attach<T>(T component)
+            where T : class 
+        {
+            var mapper = _componentManager.GetMapper<T>();
+            mapper.Put(Id, component);
+        }
+
+        public void Detach<T>()
+            where T : class
+        {
+            var mapper = _componentManager.GetMapper<T>();
+            mapper.Delete(Id);
+        }
+
+        public T Get<T>()
+            where T : class 
+        {
+            var mapper = _componentManager.GetMapper<T>();
+            return mapper.Get(Id);
+        }
+
+
+        public bool Has<T>() 
+            where T : class
+        {
+            return _componentManager.GetMapper<T>().Has(Id);
+        }
+
+        public void Destroy()
+        {
+            _entityManager.Destroy(Id);
+        }
+
+        public bool Equals(Entity other)
+        {
+            if (ReferenceEquals(null, other)) return false;
+            if (ReferenceEquals(this, other)) return true;
+            return Id == other.Id;
+        }
+
+        public override bool Equals(object obj)
+        {
+            if (ReferenceEquals(null, obj)) return false;
+            if (ReferenceEquals(this, obj)) return true;
+            if (obj.GetType() != GetType()) return false;
+            return Equals((Entity) obj);
+        }
+
+        public override int GetHashCode()
+        {
+            // ReSharper disable once NonReadonlyMemberInGetHashCode
+            return Id;
+        }
+
+        public static bool operator ==(Entity left, Entity right)
+        {
+            return Equals(left, right);
+        }
+
+        public static bool operator !=(Entity left, Entity right)
+        {
+            return !Equals(left, right);
+        }
+    }
+}
\ No newline at end of file
diff --git a/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/EntityManager.cs b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/EntityManager.cs
new file mode 100644
index 0000000..5e1d28a
--- /dev/null
+++ b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/EntityManager.cs
@@ -0,0 +1,120 @@
+using System;
+using System.Collections.Generic;
+using System.Collections.Specialized;
+using System.Diagnostics;
+using System.Linq;
+using Microsoft.Xna.Framework;
+using MonoGame.Extended.Collections;
+using MonoGame.Extended.Entities.Systems;
+
+namespace MonoGame.Extended.Entities
+{
+    public class EntityManager : UpdateSystem
+    {
+        private const int _defaultBagSize = 128;
+
+        public EntityManager(ComponentManager componentManager)
+        {
+            _componentManager = componentManager;
+            _addedEntities = new Bag<int>(_defaultBagSize);
+            _removedEntities = new Bag<int>(_defaultBagSize);
+            _changedEntities = new Bag<int>(_defaultBagSize);
+            _entityToComponentBits = new Bag<BitVector32>(_defaultBagSize);
+            _componentManager.ComponentsChanged += OnComponentsChanged;
+
+            _entityBag = new Bag<Entity>(_defaultBagSize);
+            _entityPool = new Pool<Entity>(() => new Entity(_nextId++, this, _componentManager), _defaultBagSize);
+        }
+
+        private readonly ComponentManager _componentManager;
+        private int _nextId;
+
+        public int Capacity => _entityBag.Capacity;
+        public IEnumerable<int> Entities => _entityBag.Where(e => e != null).Select(e => e.Id);
+        public int ActiveCount { get; private set; }
+
+        private readonly Bag<Entity> _entityBag;
+        private readonly Pool<Entity> _entityPool;
+        private readonly Bag<int> _addedEntities;
+        private readonly Bag<int> _removedEntities;
+        private readonly Bag<int> _changedEntities;
+        private readonly Bag<BitVector32> _entityToComponentBits;
+
+        public event Action<int> EntityAdded;
+        public event Action<int> EntityRemoved;
+        public event Action<int> EntityChanged;
+
+        public Entity Create()
+        {
+            var entity = _entityPool.Obtain();
+            var id = entity.Id;
+            Debug.Assert(_entityBag[id] == null);
+            _entityBag[id] = entity;
+            _addedEntities.Add(id);
+            _entityToComponentBits[id] = new BitVector32(0);
+            return entity;
+        }
+
+        public void Destroy(int entityId)
+        {
+            if (!_removedEntities.Contains(entityId))
+                _removedEntities.Add(entityId);
+        }
+
+        public void Destroy(Entity entity)
+        {
+            Destroy(entity.Id);
+        }
+
+        public Entity Get(int entityId)
+        {
+            return _entityBag[entityId];
+        }
+
+        public BitVector32 GetComponentBits(int entityId)
+        {
+            return _entityToComponentBits[entityId];
+        }
+
+        private void OnComponentsChanged(int entityId)
+        {
+            _changedEntities.Add(entityId);
+            _entityToComponentBits[entityId] = _componentManager.CreateComponentBits(entityId);
+            EntityChanged?.Invoke(entityId);
+        }
+
+        public override void Update(GameTime gameTime)
+        {
+            foreach (var entityId in _addedEntities)
+            {
+                _entityToComponentBits[entityId] = _componentManager.CreateComponentBits(entityId);
+                ActiveCount++;
+                EntityAdded?.Invoke(entityId);
+            }
+
+            foreach (var entityId in _changedEntities)
+            {
+                _entityToComponentBits[entityId] = _componentManager.CreateComponentBits(entityId);
+                EntityChanged?.Invoke(entityId);
+            }
+
+            foreach (var entityId in _removedEntities)
+            {
+                // we must notify subscribers before removing it from the pool
+                // otherwise an entity system could still be using the entity when the same id is obtained.
+                EntityRemoved?.Invoke(entityId);
+
+                var entity = _entityBag[entityId];
+                _entityBag[entityId] = null;
+                _componentManager.Destroy(entityId);
+                _entityToComponentBits[entityId] = default(BitVector32);
+                ActiveCount--;
+                _entityPool.Free(entity);
+            }
+
+            _addedEntities.Clear();
+            _removedEntities.Clear();
+            _changedEntities.Clear();
+        }
+    }
+}
diff --git a/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/EntitySubscription.cs b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/EntitySubscription.cs
new file mode 100644
index 0000000..6766b0f
--- /dev/null
+++ b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/EntitySubscription.cs
@@ -0,0 +1,61 @@
+using System;
+using MonoGame.Extended.Collections;
+
+namespace MonoGame.Extended.Entities
+{
+    internal class EntitySubscription : IDisposable
+    {
+        private readonly Bag<int> _activeEntities;
+        private readonly EntityManager _entityManager;
+        private readonly Aspect _aspect;
+        private bool _rebuildActives;
+
+        internal EntitySubscription(EntityManager entityManager, Aspect aspect)
+        {
+            _entityManager = entityManager;
+            _aspect = aspect;
+            _activeEntities = new Bag<int>(entityManager.Capacity);
+            _rebuildActives = true;
+
+            _entityManager.EntityAdded += OnEntityAdded;
+            _entityManager.EntityRemoved += OnEntityRemoved;
+            _entityManager.EntityChanged += OnEntityChanged;
+        }
+
+        private void OnEntityAdded(int entityId)
+        {
+            if (_aspect.IsInterested(_entityManager.GetComponentBits(entityId)))
+                _activeEntities.Add(entityId);
+        }
+
+        private void OnEntityRemoved(int entityId) => _rebuildActives = true;
+        private void OnEntityChanged(int entityId) => _rebuildActives = true;
+
+        public void Dispose()
+        {
+            _entityManager.EntityAdded -= OnEntityAdded;
+            _entityManager.EntityRemoved -= OnEntityRemoved;
+        }
+
+        public Bag<int> ActiveEntities
+        {
+            get
+            {
+                if (_rebuildActives)
+                    RebuildActives();
+
+                return _activeEntities;
+            }
+        }
+
+        private void RebuildActives()
+        {
+            _activeEntities.Clear();
+
+            foreach (var entity in _entityManager.Entities)
+                OnEntityAdded(entity);
+
+            _rebuildActives = false;
+        }
+    }
+}
\ No newline at end of file
diff --git a/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/MonoGame.Extended.Entities.csproj b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/MonoGame.Extended.Entities.csproj
new file mode 100644
index 0000000..21ca693
--- /dev/null
+++ b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/MonoGame.Extended.Entities.csproj
@@ -0,0 +1,12 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <Description>An Entity Component System to make MonoGame more awesome.</Description>
+    <PackageTags>monogame ecs entity component system</PackageTags>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\MonoGame.Extended\MonoGame.Extended.csproj" />
+  </ItemGroup>
+
+</Project>
diff --git a/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/Systems/DrawSystem.cs b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/Systems/DrawSystem.cs
new file mode 100644
index 0000000..b9e63eb
--- /dev/null
+++ b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/Systems/DrawSystem.cs
@@ -0,0 +1,16 @@
+using Microsoft.Xna.Framework;
+
+namespace MonoGame.Extended.Entities.Systems
+{
+    public interface IDrawSystem : ISystem
+    {
+        void Draw(GameTime gameTime);
+    }
+
+    public abstract class DrawSystem : IDrawSystem
+    {
+        public virtual void Dispose() { }
+        public virtual void Initialize(World world) { }
+        public abstract void Draw(GameTime gameTime);
+    }
+}
\ No newline at end of file
diff --git a/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/Systems/EntityDrawSystem.cs b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/Systems/EntityDrawSystem.cs
new file mode 100644
index 0000000..5a0d6b9
--- /dev/null
+++ b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/Systems/EntityDrawSystem.cs
@@ -0,0 +1,14 @@
+using Microsoft.Xna.Framework;
+
+namespace MonoGame.Extended.Entities.Systems
+{
+    public abstract class EntityDrawSystem : EntitySystem, IDrawSystem
+    {
+        protected EntityDrawSystem(AspectBuilder aspect)
+            : base(aspect)
+        {
+        }
+
+        public abstract void Draw(GameTime gameTime);
+    }
+}
\ No newline at end of file
diff --git a/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/Systems/EntityProcessingSystem.cs b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/Systems/EntityProcessingSystem.cs
new file mode 100644
index 0000000..c4d9339
--- /dev/null
+++ b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/Systems/EntityProcessingSystem.cs
@@ -0,0 +1,26 @@
+using Microsoft.Xna.Framework;
+
+namespace MonoGame.Extended.Entities.Systems
+{
+    public abstract class EntityProcessingSystem : EntityUpdateSystem
+    {
+        protected EntityProcessingSystem(AspectBuilder aspectBuilder)
+            : base(aspectBuilder)
+        {
+        }
+
+        public override void Update(GameTime gameTime)
+        {
+            Begin();
+
+            foreach (var entityId in ActiveEntities)
+                Process(gameTime, entityId);
+
+            End();
+        }
+
+        public virtual void Begin() { }
+        public abstract void Process(GameTime gameTime, int entityId);
+        public virtual void End() { }
+    }
+}
\ No newline at end of file
diff --git a/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/Systems/EntitySystem.cs b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/Systems/EntitySystem.cs
new file mode 100644
index 0000000..2c95107
--- /dev/null
+++ b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/Systems/EntitySystem.cs
@@ -0,0 +1,51 @@
+using MonoGame.Extended.Collections;
+
+namespace MonoGame.Extended.Entities.Systems
+{
+    public abstract class EntitySystem : ISystem
+    {
+        protected EntitySystem(AspectBuilder aspectBuilder)
+        {
+            _aspectBuilder = aspectBuilder;
+        }
+
+        public void Dispose()
+        {
+            if (_world != null)
+            {
+                _world.EntityManager.EntityAdded -= OnEntityAdded;
+                _world.EntityManager.EntityRemoved -= OnEntityRemoved;
+            }
+        }
+
+        private readonly AspectBuilder _aspectBuilder;
+        private EntitySubscription _subscription;
+
+        private World _world;
+
+        protected virtual void OnEntityChanged(int entityId) { }
+        protected virtual void OnEntityAdded(int entityId) { }
+        protected virtual void OnEntityRemoved(int entityId) { }
+
+        public Bag<int> ActiveEntities => _subscription.ActiveEntities;
+
+        public virtual void Initialize(World world)
+        {
+            _world = world;
+
+            var aspect = _aspectBuilder.Build(_world.ComponentManager);
+            _subscription = new EntitySubscription(_world.EntityManager, aspect);
+            _world.EntityManager.EntityAdded += OnEntityAdded;
+            _world.EntityManager.EntityRemoved += OnEntityRemoved;
+            _world.EntityManager.EntityChanged += OnEntityChanged;
+
+            Initialize(world.ComponentManager);
+        }
+
+        public abstract void Initialize(IComponentMapperService mapperService);
+
+        protected void DestroyEntity(int entityId) => _world.DestroyEntity(entityId);
+        protected Entity CreateEntity() => _world.CreateEntity();
+        protected Entity GetEntity(int entityId) => _world.GetEntity(entityId);
+    }
+}
\ No newline at end of file
diff --git a/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/Systems/EntityUpdateSystem.cs b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/Systems/EntityUpdateSystem.cs
new file mode 100644
index 0000000..97a61d5
--- /dev/null
+++ b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/Systems/EntityUpdateSystem.cs
@@ -0,0 +1,14 @@
+using Microsoft.Xna.Framework;
+
+namespace MonoGame.Extended.Entities.Systems
+{
+    public abstract class EntityUpdateSystem : EntitySystem, IUpdateSystem
+    {
+        protected EntityUpdateSystem(AspectBuilder aspectBuilder) 
+            : base(aspectBuilder)
+        {
+        }
+
+        public abstract void Update(GameTime gameTime);
+    }
+}
\ No newline at end of file
diff --git a/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/Systems/ISystem.cs b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/Systems/ISystem.cs
new file mode 100644
index 0000000..d4511fc
--- /dev/null
+++ b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/Systems/ISystem.cs
@@ -0,0 +1,9 @@
+using System;
+
+namespace MonoGame.Extended.Entities.Systems
+{
+    public interface ISystem : IDisposable
+    {
+        void Initialize(World world);
+    }
+}
\ No newline at end of file
diff --git a/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/Systems/UpdateSystem.cs b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/Systems/UpdateSystem.cs
new file mode 100644
index 0000000..e85c964
--- /dev/null
+++ b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/Systems/UpdateSystem.cs
@@ -0,0 +1,16 @@
+using Microsoft.Xna.Framework;
+
+namespace MonoGame.Extended.Entities.Systems
+{
+    public interface IUpdateSystem : ISystem
+    {
+        void Update(GameTime gameTime);
+    }
+
+    public abstract class UpdateSystem : IUpdateSystem
+    {
+        public virtual void Dispose() { }
+        public virtual void Initialize(World world) { }
+        public abstract void Update(GameTime gameTime);
+    }
+}
\ No newline at end of file
diff --git a/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/World.cs b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/World.cs
new file mode 100644
index 0000000..022d4b8
--- /dev/null
+++ b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/World.cs
@@ -0,0 +1,84 @@
+using Microsoft.Xna.Framework;
+using MonoGame.Extended.Collections;
+using MonoGame.Extended.Entities.Systems;
+
+namespace MonoGame.Extended.Entities
+{
+    public class World : SimpleDrawableGameComponent
+    {
+        private readonly Bag<IUpdateSystem> _updateSystems;
+        private readonly Bag<IDrawSystem> _drawSystems;
+
+        internal World()
+        {
+            _updateSystems = new Bag<IUpdateSystem>();
+            _drawSystems = new Bag<IDrawSystem>();
+
+            RegisterSystem(ComponentManager = new ComponentManager());
+            RegisterSystem(EntityManager = new EntityManager(ComponentManager));
+        }
+
+        public override void Dispose()
+        {
+            foreach (var updateSystem in _updateSystems)
+                updateSystem.Dispose();
+
+            foreach (var drawSystem in _drawSystems)
+                drawSystem.Dispose();
+
+            _updateSystems.Clear();
+            _drawSystems.Clear();
+            
+            base.Dispose();
+        }
+
+        internal EntityManager EntityManager { get; }
+        internal ComponentManager ComponentManager { get; }
+
+        public int EntityCount => EntityManager.ActiveCount;
+
+        internal void RegisterSystem(ISystem system)
+        {
+            // ReSharper disable once ConvertIfStatementToSwitchStatement
+            if (system is IUpdateSystem updateSystem)
+                _updateSystems.Add(updateSystem);
+
+            if (system is IDrawSystem drawSystem)
+                _drawSystems.Add(drawSystem);
+
+            system.Initialize(this);
+        }
+
+        public Entity GetEntity(int entityId)
+        {
+            return EntityManager.Get(entityId);
+        }
+
+        public Entity CreateEntity()
+        {
+            return EntityManager.Create();
+        }
+
+        public void DestroyEntity(int entityId)
+        {
+            EntityManager.Destroy(entityId);
+        }
+
+        public void DestroyEntity(Entity entity)
+        {
+            EntityManager.Destroy(entity);
+        }
+        
+        public override void Update(GameTime gameTime)
+        {
+            foreach (var system in _updateSystems)
+                system.Update(gameTime);
+        }
+
+        public override void Draw(GameTime gameTime)
+        {
+            foreach (var system in _drawSystems)
+                system.Draw(gameTime);
+        }
+    }
+}
\ No newline at end of file
diff --git a/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/WorldBuilder.cs b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/WorldBuilder.cs
new file mode 100644
index 0000000..7f03323
--- /dev/null
+++ b/Plugins/MonoGame.Extended/source/MonoGame.Extended.Entities/WorldBuilder.cs
@@ -0,0 +1,26 @@
+using System.Collections.Generic;
+using MonoGame.Extended.Entities.Systems;
+
+namespace MonoGame.Extended.Entities
+{
+    public class WorldBuilder
+    {
+        private readonly List<ISystem> _systems = new List<ISystem>();
+
+        public WorldBuilder AddSystem(ISystem system)
+        {
+            _systems.Add(system);
+            return this;
+        }
+
+        public World Build()
+        {
+            var world = new World();
+
+            foreach (var system in _systems)
+                world.RegisterSystem(system);
+
+            return world;
+        }
+    }
+}
\ No newline at end of file