Entitas++

Entitas++ is a fast Entity Component System Framework (ECS) C++11 port of Entitas v0.29.0 for C# and Unity.

There are some differences between both, so please check the code and notes below !

Any feedback is welcome !

Documentation

Overview

As in Entitas C#, basic code architecture is the same:

+------------------+
|       Pool       |
|------------------|
|    e       e     |      +-----------+
|        e     e---|----> |  Entity   |
|  e        e      |      |-----------|
|     e  e       e |      | Component |
| e            e   |      |           |      +-----------+
|    e     e       |      | Component-|----> | Component |
|  e    e     e    |      |           |      |-----------|
|    e      e    e |      | Component |      |   Data    |
+------------------+      +-----------+      +-----------+
  |
  |
  |     +-------------+  Groups:
  |     |      e      |  Subsets of entities in the pool
  |     |   e     e   |  for blazing fast querying
  +---> |        +------------+
        |     e  |    |       |
        |  e     | e  |  e    |
        +--------|----+    e  |
                 |     e      |
                 |  e     e   |
                 +------------+

Creating a new component example

Entitas C#

public class PositionComponent : IComponent {
    public float x;
    public float y;
    public float z;
}

//...

var pool = new Pool(ComponentIds.TotalComponents);
var e = pool.CreateEntity();

e.AddPosition(1f, 2f, 3f);
e.ReplacePosition(3f, 2f, 1f);
e.RemovePosition();

var posX = e.position.x;
var hasPosition = e.hasPosition;

Entitas++

// I suggest you to use structs instead, they are the same and all members/methods are public by default.
class Position : public IComponent {
    public:
        // You must provide at least ONE public "Reset" method with any parameters you want
        void Reset(float px, float py, float pz) {
            x = px;
            y = py;
            z = pz;
        }

        float x;
        float y;
        float z;
};

//...

auto pool = new Pool();
auto e = pool->CreateEntity();

e->Add<Position>(1f, 2f, 3f);
e->Replace<Position>(3f, 2f, 1f);
e->Remove<Position>();

float posX = e->Get<Position>()->x;
bool hasPosition = e->Has<Position>();

Basic component management

Entitas C#

entity.AddPosition(3, 7);
entity.AddHealth(100);
entity.isMovable = true;

entity.ReplacePosition(10, 100);
entity.ReplaceHealth(entity.health.value - 1);
entity.isMovable = false;

entity.RemovePosition();

var hasPos = entity.hasPosition;
var movable = entity.isMovable;

Entitas++

entity->Add<Position>(3, 7);
entity->Add<Health>(100);
entity->Replace<Movable>(); // There is no helper in here, you must use "Replace" and "Remove" methods

entity->Replace<Position>(10, 100);
entity->Replace<Health>(entity->Get<Health>()->value - 1);
entity->Remove<Movable>();

entity->Remove<Position>();

bool hasPos = entity->Has<Position>();
bool movable = entity->Has<Movable>(); // Again, you must use "Has" to check if an entity has a component

Pools

Entitas C#

// Pools.pool is kindly generated for you by the code generator
var pool = Pools.pool;
var entity = pool.CreateEntity();
entity.isMovable = true;

// Returns all entities having MovableComponent and PositionComponent.
// Matchers are also generated for you.
var entities = pool.GetEntities(Matcher.AllOf(Matcher.Movable, Matcher.Position));
foreach (var e in entities) {
    // do something
}

Entitas++

// No code generator == no "Pools". You must handle yourself your Pools !
auto pool = new Pool();
auto entity = pool->CreateEntity();
entity->Replace<Movable>(); // I used "Replace" but in this case is better to use "Add" directly

// Returns all entities having MovableComponent and PositionComponent.
// Matchers are also generated for you.
auto entities = pool->GetEntities(Matcher_AllOf(Movable, Position)); // *Some magic preprocessor involved*
for (auto &e : entities) { // e is a shared_ptr of Entity
    // do something
}

Group events

Entitas C#

pool.GetGroup(Matcher.Position).OnEntityAdded += (group, entity, index, component) => {
    // Do something
};

Entitas++

pool->GetGroup(Matcher_AllOf(Position))->OnEntityAdded += [](std::shared_ptr<Group> group, EntityPtr entity, ComponentId index, IComponent* component) {
    // Do something
};

Group Observer

Entitas C#

var group = pool.GetGroup(Matcher.Position);
var observer = group.CreateObserver(GroupEventType.OnEntityAdded);
foreach (var e in observer.collectedEntities) {
    // do something
}
observer.ClearCollectedEntities();

Entitas++

auto group = pool->GetGroup(Matcher_AllOf(Position)); // There are _AnyOf and _NoneOf too !
auto observer = group->CreateObserver(GroupEventType::OnEntityAdded);
for (auto &e : observer->GetCollectedEntities()) {
    // do something
}
observer->ClearCollectedEntities();

Execute Systems

Entitas C#

public class MoveSystem : IExecuteSystem, ISetPool {
    Group _group;

    public void SetPool(Pool pool) {
        _group = pool.GetGroup(Matcher.AllOf(Matcher.Move, Matcher.Position));
    }

    public void Execute() {
        foreach (var e in _group.GetEntities()) {
            var move = e.move;
            var pos = e.position;
            e.ReplacePosition(pos.x, pos.y + move.speed, pos.z);
        }
    }
}

Entitas++

class MoveSystem : public IExecuteSystem, public ISetPool {
    std::weak_ptr<Group> _group;

    public:
        void SetPool(Pool* pool) {
            _group = pool->GetGroup(Matcher_AllOf(Move, Position));
        }

        void Execute() {
            for (auto &e : _group.lock()->GetEntities()) {
                auto move = e->Get<Move>();
                auto pos = e->Get<Position>();
                e->Replace<Position>(pos->x, pos->y + move->speed, pos->z);
            }
        }
};

Reactive Systems

Entitas C#

public class RenderPositionSystem : IReactiveSystem {
    public TriggerOnEvent trigger { get { return Matcher.AllOf(Matcher.Position, Matcher.View).OnEntityAdded(); } }

    public void Execute(List<Entity> entities) {
        // Gets executed only if the observed group changed.
        // Changed entities are passed as an argument
        foreach (var e in entities) {
            var pos = e.position;
            e.view.gameObject.transform.position = new Vector3(pos.x, pos.y, pos.z);
        }
    }
}

Entitas++

class RenderPositionSystem : public IReactiveSystem {
    public:
        RenderPositionSystem() {
        	trigger = Matcher_AllOf(Position, View).OnEntityAdded();
        }

        void Execute(std::vector<EntityPtr> entities) {
            // Gets executed only if the observed group changed.
            // Changed entities are passed as an argument
            for (auto &e : entities) {
                auto pos = e->Get<Position>();
                // NOTE: Unity-only example, but this maybe could be the code if Unity were compatible with C++
                e->Get<View>()->gameObject.transform.position = new Vector3(pos->x, pos->y, pos->z);
            }
        }
}

Notes

• All code above was written using: using namespace EntitasPP;, if you don't, you must prepend all the classes with the namespace EntitasPP::.
• There is no code generator because C++ lacks of code reflection. So all code must be done by you, but there are a lot of templating involved in here to ease the work for you anyways (see code above).
• 'Systems' class was renamed to 'SystemContainer'. You can see a simple example of use in the provided 'main.cpp'.
• All 'ToString()' methods were removed. If you need to track identifiers between entities I suggest you to use your own custom Component.
• AERC (Automatic Entity Reference Counting) was implemented using smart pointers. (Yeah! Take that C# 😜)

If you need more documentation of the architecture of the framework, please go to Entitas v0.29.0 C# Wiki since this framework has a lot on common with the original C# one.

The MIT License (MIT)

Copyright © 2020 Juan Delgado (JuDelCo)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.