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https://github.com/judelco/entitas-cpp

Entitas++ is a fast Entity Component System (ECS) C++11 port of Entitas C#
https://github.com/judelco/entitas-cpp

cpp design-pattern ecs entitas entity entity-component entity-component-system entity-framework game game-development game-engine gamedev performance

Last synced: 3 months ago
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Entitas++ is a fast Entity Component System (ECS) C++11 port of Entitas C#

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README 

        
Entitas++

=====================



Entitas++ is a fast Entity Component System Framework (ECS) C++11 port of [Entitas v0.29.0 for C# and Unity](https://github.com/sschmid/Entitas-CSharp/tree/0.29.0).



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#

```csharp

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++

```cpp

// 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(1f, 2f, 3f);

e->Replace(3f, 2f, 1f);

e->Remove();



float posX = e->Get()->x;

bool hasPosition = e->Has();

```



#### Basic component management



###### Entitas C#

```csharp

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++

```cpp

entity->Add(3, 7);

entity->Add(100);

entity->Replace(); // There is no helper in here, you must use "Replace" and "Remove" methods



entity->Replace(10, 100);

entity->Replace(entity->Get()->value - 1);

entity->Remove();



entity->Remove();



bool hasPos = entity->Has();

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

```



#### Pools



###### Entitas C#

```csharp

// 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++

```cpp

// No code generator == no "Pools". You must handle yourself your Pools !

auto pool = new Pool();

auto entity = pool->CreateEntity();

entity->Replace(); // 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#

```csharp

pool.GetGroup(Matcher.Position).OnEntityAdded += (group, entity, index, component) => {

    // Do something

};

```



###### Entitas++

```cpp

pool->GetGroup(Matcher_AllOf(Position))->OnEntityAdded += [](std::shared_ptr group, EntityPtr entity, ComponentId index, IComponent* component) {

    // Do something

};

```



#### Group Observer



###### Entitas C#

```csharp

var group = pool.GetGroup(Matcher.Position);

var observer = group.CreateObserver(GroupEventType.OnEntityAdded);

foreach (var e in observer.collectedEntities) {

    // do something

}

observer.ClearCollectedEntities();

```



###### Entitas++

```cpp

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#

```csharp

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++

```cpp

class MoveSystem : public IExecuteSystem, public ISetPool {

    std::weak_ptr _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();

                auto pos = e->Get();

                e->Replace(pos->x, pos->y + move->speed, pos->z);

            }

        }

};

```



#### Reactive Systems



###### Entitas C#

```csharp

public class RenderPositionSystem : IReactiveSystem {

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



    public void Execute(List 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++

```cpp

class RenderPositionSystem : public IReactiveSystem {

    public:

        RenderPositionSystem() {

        	trigger = Matcher_AllOf(Position, View).OnEntityAdded();

        }



        void Execute(std::vector entities) {

            // Gets executed only if the observed group changed.

            // Changed entities are passed as an argument

            for (auto &e : entities) {

                auto pos = e->Get();

                // NOTE: Unity-only example, but this maybe could be the code if Unity were compatible with C++

                e->Get()->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](https://en.wikipedia.org/wiki/Reflection_(computer_programming)). 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](https://github.com/sschmid/Entitas-CSharp/blob/94ab9b172987a65a7facfd4c383b621a4cbb0bca/Entitas/Entitas/Systems.cs#L8) 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# :stuck_out_tongue_winking_eye:)



If you need more documentation of the architecture of the framework, please go to [Entitas v0.29.0 C# Wiki](https://github.com/sschmid/Entitas-CSharp/wiki/Home/18f70d987d94be972c179bbd71b3a175263c0f04) 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.