Cocos2dx b2body.def 如何设置坐标

大家好，
刚学android，做个小程序需要用到cocos2dx的引擎，在极客学院上学flappy bird的课程，现在问题是不管是自己写的代码还是直接下载的代码，编译后在屏幕上都看不见图像，只有黑色的背景，代码如下

void FlappyBird::addBird()
{ 
bird = B2Sprite::create("bird.png");
CCSize size = bird->getContentSize();

b2BodyDef bodyDef;
bodyDef.type = b2_dynamicBody;
bodyDef.position = b2Vec2(screenSize.width/2/RATIO, 9);
//bodyDef.position = b2Vec2(0.0f, 5.0f);
b2Body *birdBody = world->CreateBody(&bodyDef);

b2PolygonShape birdShape;
birdShape.SetAsBox(size.width/2/RATIO, size.height/2/RATIO);

b2FixtureDef birdFixtureDef;
birdFixtureDef.shape = &birdShape;
birdBody->CreateFixture(&birdFixtureDef);

bird->setPTMRatio(RATIO);
bird->setB2Body(birdBody);
addChild(bird);
}

屏幕大小设置为480*320，RATIO＝48，将b2vec2改称(0.0f,5.0f)也不对，大家知道哪里错了吗？

教程链接：http://www.jikexueyuan.com/course/show/id/34.html