CCSprite不是COCOS2dx中的物理体吗？

Question

我有以下功能，它在cocos2dx中初始化了场景，据我所知，我做的一切都是正确的。但我的CCSprite仍然不是一个物理体。它保持静止在屏幕的中心，而它应该下降并受到重力的影响。

任何帮助都将不胜感激。提前谢谢。

void HelloWorld::initPhysics()
{
CCSize visibleSize = CCDirector::sharedDirector()->getVisibleSize();
CCPoint origin = CCDirector::sharedDirector()->getVisibleOrigin();
CCSize screenSize = CCDirector::sharedDirector()->getWinSize();
//creating the world
b2Vec2 gravity;
gravity.Set(0.0f, -20.0f);
world = new b2World(gravity);

// Do we want to let bodies sleep?
world->SetAllowSleeping(true);

world->SetContinuousPhysics(true);


CCSprite* bird = CCSprite::create("Harry@2x.png");
bird->setScale(2.0);
bird->setPosition(ccp(visibleSize.width/2, visibleSize.height/2));
addChild(bird);

b2Body *_body;
// Create ball body and shape
b2BodyDef ballBodyDef;
ballBodyDef.type = b2_dynamicBody;
ballBodyDef.position.Set(screenSize.width,screenSize.height);
ballBodyDef.userData = bird;
_body = world->CreateBody(&ballBodyDef);

b2CircleShape circle;
circle.m_radius = 26.0/PTM_RATIO;

b2FixtureDef ballShapeDef;
ballShapeDef.shape = &circle;
ballShapeDef.density = 100.0f;
ballShapeDef.friction = 0.5f;
ballShapeDef.restitution = 0.7f;
_body->CreateFixture(&ballShapeDef);
}

这是我的更新函数，我将world变量添加为全局变量。

void HelloWorld::update(float dt)
{
int velocityIterations = 8;
int positionIterations = 1;

world->Step(dt, velocityIterations, positionIterations);

//Iterate over the bodies in the physics world
for (b2Body* b = world->GetBodyList(); b; b = b->GetNext())
{
    if (b->GetUserData() != NULL) {
        //Synchronize the AtlasSprites position and rotation with the corresponding body
        CCSprite* myActor = (CCSprite*)b->GetUserData();
        myActor->setPosition( CCPointMake( b->GetPosition().x * PTM_RATIO, b->GetPosition().y * PTM_RATIO) );
        myActor->setRotation( -1 * CC_RADIANS_TO_DEGREES(b->GetAngle()) );
    }
}
}

Answer 1

b2World* world是一个局部变量。这意味着它将超出当前函数末尾的范围，这意味着您无法调用world->Step(..)方法--为了提高物理世界的状态，必须定期调用该方法(通常是每一帧)。不踏入世界，就不会有任何运动。