Handler

CameraHandler.hpp

class CameraHandler {
	public:
		CameraHandler();
		
		Handler<CameraHandler> *getArcballHandler();
	
		void handleKey(Handler<CameraHandler> *, int, int);
                void handleMouseButton(Handler<CameraHandler> *, int, int);
                void handleMousePosition(Handler<CameraHandler> *, int, int);
                void handleMouseWheel(Handler<CameraHandler> *, int);
	private:
		Camera *camera;
		FPSModifier *fpsModifier;
		Arcball *arcball;
		ArcballCameraModifier *arcModifier;
		Handler<CameraHandler> *arcballHandler;
};


void CameraHandler::handleKey(Handler<CameraHandler> *handler, int key, int action) {
	if(handler == arcballHandler) {
		// Modify 'arcball' using 'key' and 'action'.
		arcModifier.Update();
	}
}

// Same with CameraHandler::handleMousePosition, etc.

Game.cpp

void Game::handleKey(int key, int action, UserData *) {
	Handler<CameraHandler> *handler = getCurrentHandler();
	handler->handleKey(key, action);
}

Handler.hpp

template <typename T> class Handler {
	public:
		Handler();
	
		void handleKey(int, int);
		void handleMousePosition(int, int);
		void handleMouseButton(int, int);
		void handleMouseWheel(int);
	private:
		T *target;
};

template <typename T, typename E> Handler<T, E>::Handler(T *t) : target(t) {}

template <typename T, typename E> void Handler<T, E>::handleKey(int a, int b) {
	target->handleKey(this, a, b);
}

template <typename T, typename E> void Handler<T, E>::handleMousePosition(int a, int b) {
	target->handleMousePosition(this, a, b);
}

template <typename T, typename E> void Handler<T, E>::handleMouseButton(int a, int b) {
	target->handleMouseButton(this, a, b);
}

template <typename T, typename E> void Handler<T, E>::handleMouseWheel(int a) {
	target->handleWheel(this, a);
}