Game Engine Architecture

754 14. Runtime Gameplay Foundation Systems

to return null when dereferenced rather than returning a pointer to object B

unexpectedly.

The following code snippet shows how a simple handle class might be

implemented. Notice that we’ve also included the handle index in the Game

Object class itself—this allows us to create new handles to a GameObject

very quickly without having to search the handle table for its address to de-

termine its handle table index.

// Within the GameObject class, we store a unique id,

// and also the object’s handle index, for efficient

// creation of new handles.

classGameObject

{

private:

// ...

GameObjectId m_uniqueId; // object’s unique id

U32 m_handleIndex; // speedier handle

// creation

friend class GameObjectHandle; // access to id and

// index

// ...

public:

GameObject() // constructor

{

// The unique id might come from the world editor,

// or it might be assigned dynamically at runtime.

m_uniqueId = AssignUniqueObjectId();

// The handle index is assigned by finding the

// first free slot in the handle table.

m_handleIndex = FindFreeSlotInHandleTable();

// ...

}

// ...

};

// This constant defines the size of the handle table,

// and hence the maximum number of game objects that can

// exist at any one time.

static const U32 MAX_GAME_OBJECTS = ...;

// This is the global handle table -- a simple array of

// pointers to GameObjects.

static GameObject* g_apGameObject[MAX_GAME_OBJECTS];