Entity Manager

The Entity Manager is an object that coordinates the entity-component system. It is intended to act as the main point of interface for game logic to create Entities and register them with Components.

At the basic level, once it has been initialized and all the Components have been registered, then the game can simply call EntityManager::UpdateComponents() once per frame.

Registering Components

You must register each Component in your game with the Entity Manager by calling EntityManager::RegisterComponent<T>().

Note: The order that you register Components with the EntityManager is the order that they will be executed in.

EntityManager entity_manager;

MyComponent my_component;
MyOtherComponent my_other_component;

// The order that Components are registered is the order that they will execute in.
entity_manager.RegisterComponent<MyComponent>(&my_component);
entity_manager.RegisterComponent<MyOtherComponent>(&my_other_component);

Creating Entities

You can create entities with a call to EntityManager::AllocateNewEntity(). It returns a pointer to the newly allocated Entity as an EntityRef typedef.

EntityRef my_first_entity = entity_manager.AllocateNewEntity();
EntityRef my_second_entity = entity_manager.AllocateNewEntity();

Add Entities to Components

You can interchangeably add Entities to Components. This is done with a call to EntityManager::AddEntityToComponent<T>().

// Associate `my_first_entity` with `MyComponent`.
entity_manager.AddEntityToComponent<MyComponent>(my_first_entity);

// Associate `my_second_entity` with both `MyComponent` and `MyOtherComponent`.
entity_manager.AddEntityToComponent<MyComponent>(my_second_entity);
entity_manager.AddEntityToComponent<MyOtherComponent>(my_second_entity);

Update all Components

Once you have registered your Components with your Entity Manager and added your Entities to your Components, then you just need to call EntityManager::UpdateComponents() once per frame with the delta_time since the last update.

while(game_is_running) {
  entity_manager.UpdateComponents(delta_time);
}