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LeoECS - Simple lightweight C# Entity Component System framework

Performance, zero/small memory allocations/footprint, no dependencies on any game engine - main goals of this project.

Tested on unity 2018.3 (not dependent on it) and contains assembly definition for compiling to separate assembly file for performance reason.

Important! Dont forget to use DEBUG builds for development and RELEASE builds in production: all internal error checks / exception throwing works only in DEBUG builds and eleminated for performance reasons in RELEASE.

Main parts of ecs

Component

Container for user data without / with small logic inside. Can be used any user class without any additional inheritance:

class WeaponComponent {
    public int Ammo;
    public string GunName;
}

Important! Dont forget to manually init all fields of new added component. Default value initializers will not work due all components can be reused automatically multiple times through builtin pooling mechanism (no destroying / creating new instance for each request for performance reason).

Important! Dont forget to cleanup reference links to instances of another components / engine classes before removing components from entity, otherwise it can lead to memory leaks.

By default all marshal-by-reference typed fields of component (classes in common case) will be checked for null on removing attempt in DEBUG-mode. If you know that you have object instance that should be not null (preinited collections for example) - [EcsIgnoreNullCheck] attribute can be used for disabling these checks.

Entity

Сontainer for components. Implemented with int id-s for more simplified api:

WeaponComponent myWeapon;
int entityId = _world.CreateEntityWith<WeaponComponent> (out myWeapon);
_world.RemoveEntity (entityId);

Dont forget that EcsWorld.CreateEntityWith method has multiple overloaded versions:

Component1 c1;
Component2 c2;
int entityId = _world.CreateEntityWith<Component1, Component2> (out c1, out c2);
_world.RemoveEntity (entityId);

Important! Entities without components on them will be automatically removed from EcsWorld right after finish execution of current system.

System

Сontainer for logic for processing filtered entities. User class should implements IEcsPreInitSystem, IEcsInitSystem or / and IEcsRunSystem interfaces:

class WeaponSystem : IEcsPreInitSystem, IEcsInitSystem {
    void IEcsPreInitSystem.PreInitialize () {
        // Will be called once during world initialization and before IEcsInitSystem.Initialize.
    }

    void IEcsInitSystem.Initialize () {
        // Will be called once during world initialization.
    }

    void IEcsInitSystem.Destroy () {
        // Will be called once during world destruction.
    }

    void IEcsPreInitSystem.PreDestroy () {
        // Will be called once during world destruction and after IEcsInitSystem.Destroy.
    }
}
class HealthSystem : IEcsRunSystem {
    void IEcsRunSystem.Run () {
        // Will be called on each EcsSystems.Run() call.
    }
}

Data injection

Important! Will not work when LEOECS_DISABLE_INJECT preprocessor constant defined.

With [EcsInject] attribute over IEcsSystem class all compatible EcsWorld and EcsFilter<T> fields of instance of this class will be auto-initialized (auto-injected):

[EcsInject]
class HealthSystem : IEcsSystem {
    EcsWorld _world = null;

    EcsFilter<WeaponComponent> _weaponFilter = null;
}

Instance of any custom type can be injected to all systems through EcsSystems.Inject method:

var systems = new EcsSystems (world)
    .Add (new TestSystem1 ())
    .Add (new TestSystem2 ())
    .Add (new TestSystem3 ())
    .Inject (a)
    .Inject (b)
    .Inject (c)
    .Inject (d);
systems.Initialize ();

Each system will be scanned for compatible fields (can contains all of them or no one) with proper initialization.

Special classes

EcsFilter

Container for keeping filtered entities with specified component list:

[EcsInject]
class WeaponSystem : IEcsInitSystem, IEcsRunSystem {
    EcsWorld _world = null;

    // We wants to get entities with "WeaponComponent" and without "HealthComponent".
    EcsFilter<WeaponComponent>.Exclude<HealthComponent> _filter = null;

    void IEcsInitSystem.Initialize () {
        _world.CreateEntityWith<WeaponComponent> ();
    }

    void IEcsInitSystem.Destroy () { }

    void IEcsRunSystem.Run () {
        foreach (var i in _filter) {
            // Components1 array will be automatically filled with instances of type "WeaponComponent".
            var weapon = _filter.Components1[i];
            weapon.Ammo = System.Math.Max (0, weapon.Ammo - 1);
        }
    }
}

All compatible entities will be stored at filter.Entities array, amount of them - at filter.EntitiesCount.

Important: filter.Entities, filter.Components1, filter.Components2, etc - can’t be iterated with foreach-loop directly, use foreach-loop over filter, or for-loop with filter.EntitiesCount value as upper-bound.

All components from filter Include constraint will be stored at filter.Components1, filter.Components2, etc - in same order as they were used in filter type declaration.

If autofilling not required (for example, for flag-based components without data), EcsIgnoreInFilter attribute can be used for decrease memory usage and increase performance:

class Component1 { }

[EcsIgnoreInFilter]
class Component2 { }

[EcsInject]
class TestSystem : IEcsSystem {
    EcsFilter<Component1, Component2> _filter;

    public Test() {
        foreach (var i in _filter) {
            // its valid code.
            var component1 = _filter.Components1[i];

            // its invalid code due to _filter.Components2 is null for memory / performance reasons.
            var component2 = _filter.Components2[i];
        }
    }
}

Important: Any filter supports up to 4 component types as “include” constraints and up to 2 component types as “exclude” constraints. Shorter constraints - better performance.

Important: If you will try to use 2 filters with same components but in different order - you will get exception with detailed info about conflicted types, but only in DEBUG mode. In RELEASE mode all checks will be skipped.

EcsWorld

Root level container for all entities / components, works like isolated environment.

Important: Do not forget to call EcsWorld.Dispose method when instance will not be used anymore.

EcsSystems

Group of systems to process EcsWorld instance:

class Startup : MonoBehaviour {
    EcsSystems _systems;

    void OnEnable() {
        // create ecs environment.
        var world = new EcsWorld ();
        _systems = new EcsSystems(world)
            .Add (new WeaponSystem ());
        _systems.Initialize ();
    }
    
    void Update() {
        // process all dependent systems.
        _systems.Run ();
        // optional behaviour for one-frame components.
        _world.RemoveOneFrameComponents ();
    }

    void OnDisable() {
        // destroy systems logical group.
        _systems.Dispose ();
        _systems = null;
        // destroy world.
        _world.Dispose ();
        _world = null;
    }
}

Important: Do not forget to call EcsSystems.Dispose method when instance will not be used anymore.

EcsSystems instance can be used as nested system (any types of IEcsPreInitSystem, IEcsInitSystem or IEcsRunSystem behaviours are supported):

// initialization
var nestedSystems = new EcsSystems (_world)
    .Add (new NestedSystem ());
// dont call nestedSystems.Initialize() here, rootSystems will do it automatically.

var rootSystems = new EcsSystems (_world)
    .Add (nestedSystems);
rootSystems.Initialize();

// update loop
// dont call nestedSystems.Run() here, rootSystems will do it automatically.
rootSystems.Run();

// destroying
// dont call nestedSystems.Dispose() here, rootSystems will do it automatically.
rootSystems.Dispose();

Sharing data between systems

If some data should be shared between systems - there are 3 ways to do it.

Custom EcsWorld class

Useful for global singleton-like access to independent systems:

class MyEcsWorld : EcsWorld {
    readonly public MyData Data;

    public MyEcsWorld(MyData data) {
        Data = data;
    }
}
var shared = new MyData();
// fill it here.
// ...
var world = new MyEcsWorld (shared);
var systems = new EcsSystems (world)
    .Add (new System1 ())
    .Add (new System2 ());
systems.Initialize();

Component with EcsFilter

Custom component can be used for this and sharing with EcsFilter:

class MyData {
    // shared data.
}
[EcsInject]
class CreateSharedData : IEcsInitSystem {
    // just to be sure that filter already created before component initialization.
    EcsFilter<MyData> _shared = null;
    EcsWorld _world = null;

    void IEcsInitSystem.Initialize () {
        var data = _world.CreateEntityWith<MyData>();
        // fill data here.
    }

    void IEcsInitSystem.Destroy () { }
}

[EcsInject]
class ReadSharedData : IEcsRunSystem {
    EcsFilter<MyData> _shared = null;

    void IEcsRunSystem.Run () {
        var data = _shared.Components1[0];
        // read data here.
    }
}

Dependency Injection

Important! Will not work when LEOECS_DISABLE_INJECT preprocessor constant defined.

External data can be shared for all systems at EcsSystems:

class MyData {
    // shared data.
}
[EcsInject]
class ReadSharedData1 : IEcsRunSystem {
    // will be automatically injected.
    MyData _shared = null;

    void IEcsRunSystem.Run () {
        // read _shared fields here.
    }
}
[EcsInject]
class ReadSharedData2 : IEcsRunSystem {
    // will be automatically injected.
    MyData _shared = null;

    void IEcsRunSystem.Run () {
        // read _shared fields here.
    }
}
//...
var shared = new MyData();
// fill it here.

var systems = new EcsSystems (world)
    .Add (new ReadSharedData1 ())
    .Add (new ReadSharedData2 ())
    .Inject (shared);
systems.Initialize ();

Examples

Snake game

Pacman game

Extensions

Reactive filters / systems

Multithreading support

Unity integration

Unity uGui event bindings

Engine independent types

License

The software released under the terms of the MIT license. Enjoy.

Donate

Its free opensource software, but you can buy me a coffee:

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FAQ

My project complex enough, I need more than 256 components. How I can do it?

There are no components limit, but for performance / memory usage reason better to keep amount of components on each entity less or equals 8.

I want to create alot of new entities with new components on start, how to speed up this process?

In this case custom component creator with predefined capacity can be used (for speed up 2x or more):

class MyComponent { }

class Startup : Monobehaviour {
    EcsSystems _systems;

    void OnEnable() {
        var world = new MyWorld (_sharedData);
        
        EcsComponentPool<MyComponent>.Instance.SetCapacity (100000);
        EcsComponentPool<MyComponent>.Instance.SetCreator (() => new MyComponent());
        
        _systems = new EcsSystems(world)
            .Add (MySystem());
        _systems.Initialize();
    }
}

I want to shrink allocated caches for my components, how I can do it?

In this case EcsComponentPool<T>.Instance.Shrink method can be used:

class MyComponent1 { }
class MyComponent2 { }

class ShrinkComponents : Monobehaviour {
    void OnEnable() {
        EcsComponentPool<MyComponent1>.Instance.Shrink ();
        EcsComponentPool<MyComponent2>.Instance.Shrink ();
    }
}

I want to process one system at MonoBehaviour.Update() and another - at MonoBehaviour.FixedUpdate(). How I can do it?

For splitting systems by MonoBehaviour-method multiple EcsSystems logical groups should be used:

EcsSystems _update;
EcsSystems _fixedUpdate;

void OnEnable() {
    var world = new EcsWorld();
    _update = new EcsSystems(world).Add(new UpdateSystem());
    _fixedUpdate = new EcsSystems(world).Add(new FixedUpdateSystem());
}

void Update() {
    _update.Run();
}

void FixedUpdate() {
    _fixedUpdate.Run();
}

I want to add new or get already exist component on entity, but GetComponent with checking result - so boring. How it can be simplified?

There is EnsureComponent method at EcsWorld, next 2 code blocks are identical:

var c1 = _world.GetComponent<C1>(id);
if (c1 == null) {
    c1 = _world.AddComponent<C1>(id);
}
...
bool isNew;
var c1 = _world.EnsureComponent<C1>(id, out isNew);

I want to add reaction on add / remove entity / components in EcsWorld. How I can do it?

It will add performance penalty and should be avoided. Anyway, LEOECS_ENABLE_WORLD_EVENTS preprocessor define can be used for this:

class MyListener : IEcsWorldEventListener {
    public void OnEntityCreated (int entity) { }
    public void OnEntityRemoved (int entity) { }
    public void OnComponentAdded (int entity, object component) { }
    public void OnComponentRemoved (int entity, object component) { }
    public void OnWorldDestroyed (EcsWorld world) { }
}

// at init code.
var listener = new MyListener();
_world.AddEventListener(listener);

// at destroy code.
_world.RemoveEventListener(listener);

I do not need dependency injection through Reflection (I heard, it’s very slooooow! / I want to use my own way to inject). How I can do it?

Builtin Reflection-based DI can be removed with LEOECS_DISABLE_INJECT preprocessor define:

  • No EcsInject attribute.
  • No automatic injection for EcsWorld and EcsFilter<T> fields.
  • Less code size.

EcsWorld should be injected somehow (for example, through constructor of system), EcsFilter<T> data can be requested through EcsWorld.GetFilter<T> method.

I do not like foreach-loops, I know that for-loops are faster. How I can use it?

Current implementation of foreach-loop fast enough (custom enumerator, no memory allocation), performance differences can be found on 10k items and more. Anyway, for-loop can be used instead foreach-loop as next in-place replacement without issues:

foreach (var i in _filter)

can be replaced with

for (int i = 0, iMax = _filter.EntitiesCount; i < iMax; i++)

I copy&paste my reset components code again and again. How I can do it in other manner?

If you want to simplify your code and keep reset-code in one place, you can use IEcsAutoResetComponent interface for components:

class MyComponent : IEcsAutoResetComponent {
    public object LinkToAnotherComponent;

    void IEcsAutoResetComponent.Reset() {
        // Cleanup all marshal-by-reference fields here.
        LinkToAnotherComponent = null;
    }
}

This method will be automatically called after component removing from entity and before recycling to component pool.

I use components as events that works only one frame, then remove it at last system in execution sequence. It’s boring, how I can automate it?

If you want to remove one-frame components without additional custom code, you can use EcsOneFrame attribute:

[EcsOneFrame]
class MyComponent { }

Important: Do not forget to call EcsWorld.RemoveOneFrameComponents method once after all EcsSystems.Run calls.

Important: Do not forget that if one-frame component contains marshal-by-reference typed fields - this component should implements IEcsAutoResetComponent interface.

I used reactive systems and filter events before, but now I can’t find them. How I can get it back?

You can implement them by yourself with EcsFilter.AddListener / EcsFilter.RemoveListener methods or use default implementation, that can be found at separate repo.

I need more than 4 components in filter, how i can do it?

Check EcsFilter<Inc1, Inc2, Inc3, Inc4> class and create new class with more components in same manner.