Entities

Overview

Entities are abstract objects, that possess only an EntityId, and can contain Components. They can only have one copy of each type of component, and they do not possess any logic of their own; relying entirely on Systems to manipulate them.

They can be created and destroyed from the World. Typically, instead of manipulating Halley::Entity objects directly, you'll be operating with Halley::EntityRef, which provides an entry point for manipulating entities.

Methods

addComponent

template <typename T> EntityRef& EntityRef::addComponent(T&& component)

Adds a component to an entity. This makes this entity be included in the families of any systems whose requirements it now fulfils. An entity can only have one component of each type. See Components for more detailed information on components, or Systems for more information on families. Returns *this.

This method can be chained, e.g.:

world->createEntity()
	.addComponent(PositionComponent(Vector2f()))
	.addComponent(CameraComponent(Camera(), 0, int(SpriteMasks::InWorld), Colour4f(0, 0, 0, 1), {}))
	.addComponent(HierarchyComponent({}, camRoot.getEntityId(), {}, true, false));

removeComponent

template <typename T> EntityRef& EntityRef::removeComponent()

Removes a component from an entity. This will cause it to be removed from any families which require that component. Returns *this.

getComponent

template <typename T> T* EntityRef::getComponent()

Returns a pointer to the specified component, or nullptr if this entity does not contain it.

getEntityId

EntityId EntityRef::getEntityId() const

Returns the Halley::EntityId of this entity. This is unique per world, and can be used to later reference this entity.