Our game's elements are all physics bodies and will have sprites to represent them visually. It is a common practice to club these two entities together. Cocos2d-x has an inbuilt class to handle this known as PhysicsSprite, but since this is our first physics game, we shall create our own class called GameObject to do the job:
class GameObject : public CCSprite
{
public:
GameObject() : game_world_(NULL), body_(NULL),
type_(E_GAME_OBJECT_NONE) {}
virtual ~GameObject();
// returns an autorelease GameObject
static GameObject* create(GameWorld* game_world,
const char* frame_name);
// accessors & mutators
inline b2Body* GetBody() { return body_; }
inline EGameObjectType GetType() { return type_; }
inline void SetType(EGameObjectType type) { type_ = type; }
virtual void Update()
{
// update position of sprite based on position of body
if(body_)
{
setPosition(ccp(WORLD_TO_SCREEN(body_->GetPosition().x),
...