Entity ID's

ID's based on properties

_ID

GUID

ID's based on objects

Game::Entity::EntityId

/// get unique id of entity EntityId GetUniqueId() const;

The entity id is given to the entity on creation by the EntityManager. The EntityManager increments an internal counter for this. In addition you can get the Game::Entity::EntityId from a Physics::Entity if you are on the physics side with this method

/// get user data int GetUserData() const;

Physics::Entity::Id

/// get the entity's unique id Id GetUniqueId() const;

So what's the problem?

Physics::Entity keeps a reference to his Game:Entity, you can use it straight out of the box if you are moving around in the physical world and would like to access some of the properties attached to the game entity. The other way round is not that easy. The documentation about entities or id's is not clear in each place. For starters it will be very confusing which id they are really holding in their hand. To give beginners an overview I have summarized the usecases. If you have only the id's you need to use the corresponding manager/server to get the corresponding entity. For game entity id's use the EntityManger, for physics entiy id's use the PhysicsServer.

The easiest way is to get the game entity from a physics entity. Ths is done by retrieving the userdata from the physics entity and feeding the EntityManager to lookup the game entity with this id.

The hard way is to get a physics entity from a game entity. The only place this information is present is in the attached properties of a game entity. Here we get to the drawbacks of named properties, you must know exactly which property has your physics entity reference stored. Mangalore so far has only two possible properties you need to query:

They are both derived from AbstractPhysicsProperty, but only the derived concrete classes are attached as properties. So if you have an entity it is best to query both properties and early out if you find a physics entity.

Lookup of Game::Entities based on collision and Physics::Entity

//physics entity from contact phys ID

Ptr  pentity = physicsServer->

	FindEntityByUniqueId(CollideContacts[i].GetEntityId());

//game entity

Ptr  entity; 



//only on a valid physics entity

if(pentity.isvalid())

{

	//use physics entity user data to lookup a game entity, 

	//can be invalid if no entity found for example in the 

	//case no userdata was set on the physics entity

	entity = Managers::EntityManager::Instance()->

		FindEntityById(pentity->GetUserData());

}

Lookup of Physics::Entity based on Game::Entity

//capital is a Game::Entity loaded or created before

//Here it gets dirty, you can only query properties 

//you know in advance possible ones would be PhysicsProperty, 

//ActorPhysicsProperty (all derived from AbstractPhysicsroperty

//But that one cannot be attached to an entity ...

if(capital->HasProperty(PhysicsProperty::RTTI))

{

	//it has this property so now we retriev it 

	//from the entiy

	PhysicsProperty *p = (PhysicsProperty *)capital->

		FindProperty(PhysicsProperty::RTTI);

	//now you can get the Physics::Entity::Id by

	//lookup via the stored Physics::Entity

	excludeSet.AddEntityId(p->GetPhysicsEntity()->

		GetUniqueId());

} 

else if(capital->HasProperty(ActorPhysicsProperty::RTTI))

{

	...

	...

}