Emerald

Entity Component System

Installation

To instal copy this folder to your project directory or an include directory

Components

To create a component all you need to do is create a class! For example

class CThing {
public:
    void saySomething() {
        std::cout << "something\n";
    }
};

class CThing2 {
    void saySomethingElse() {
        std::cout << "something else\n";
    }
};

Entity Manager

Now to create an entity manager that can use these components you would define it as

Emerald::EntityManager<CThing, CThing2> entMan;

Idealy this will be changed in a later release so you won't have to define all component types

Systems

Do create a system all that is needed is for you to create a class and inherit

Emerald::IBaseSystem<system_t>

where system_t is the type of the system you are creating, then you need to implement the method

template<typename entity_manager_t>
void update(entity_manager_t& entMan) {}

in that function you can use the method

entMan.mapEntities(m_entities, [](auto& ent) {

});

to act on all subscribed entities

and example system would be

class ASystem : ISystem<ASystem> {
public:
    template<typename entity_manager_t>
    void update(entity_manager_t& entMan) {
        entMan.mapEntities(m_entities, [](auto& ent) {
            auto& ct = ent.getComponent<CThing>();
            ct.saySomething();
        });
    }
}

to register that system to the entity manager all you need to do is

entMan.registerSystem<ASystem>()

Be careful though, there can only be one system of each type in a single entity manager

And now if you want to update the registered systems just call the function

entMan.updateSystems(time_scale);

Entities

To create an entity all you need to do is

auto id = m_entityManager.createEntity();

Emerald returns id's because it can change the location of an entity if many are added, because it stores the components continuously in memory

To get an entity and change it's component composition, do this

auto& ent = m_entityManager.getEntity(id);

and then you can use functions like

ent.addComponent<CThing>();
auto& comp = ent.getComponent<CThing>();
ent.removeComponent<CThing>();

Just be careful not to hold on to that reference for very long, because it could be invalidated

If you want to subscribe your entity to a system, do this

m_entityManager.getSystem<ASystem>().subscribe(id);

Where the id is the entities id

Disclaimer

This is in alpha, so I wouldn't count on it working perfectly under heavy load or multithreaded applications