Question

cocos2d新手简单问题,请看下代码

self.isAccelerometerEnabled = YES;
CGSize winSize = [CCDirector sharedDirector].winSize; _spriteSheet = [CCSpriteBatchNode batchNodeWithFile:@"all.png"];
[[CCSpriteFrameCache sharedSpriteFrameCache]addSpriteFramesWithFile:@"all.plist"];
[self addChild:_spriteSheet];
ball1_ = [CCSprite spriteWithSpriteFrameName:@"Bombos%20Medallion.png"];
ball1_.position = ccp(300, 200);
//精灵的旋转动作
id action13 = [CCRotateBy actionWithDuration:1 angle:-360];
id spriteRotate = [CCSequence actions:action13, nil];
id action25 = [CCRepeatForever actionWithAction:spriteRotate];
[ball1_ runAction:action25];
[_spriteSheet addChild:ball1_];
b2Vec2 gravity = b2Vec2(0.0f, 0.0f);
_world = new b2World(gravity)；
b2BodyDef groundBodyDef;
groundBodyDef.position.Set(0,0);//世界的锚点
b2Body *groundBody = _world->CreateBody(&groundBodyDef);
b2EdgeShape groundBox;
b2FixtureDef boxShapeDef;
boxShapeDef.shape =&groundBox;
groundBox.Set(b2Vec2(0,0), b2Vec2(winSize.width/PTM_RATIO, 0));
groundBody->CreateFixture(&groundBox, 0);
groundBox.Set(b2Vec2(0,0), b2Vec2(0, winSize.height/PTM_RATIO));
groundBody->CreateFixture(&groundBox, 0);
groundBox.Set(b2Vec2(0, winSize.height/PTM_RATIO),
b2Vec2(winSize.width/PTM_RATIO, winSize.height/PTM_RATIO));
groundBody->CreateFixture(&groundBox, 0);
groundBox.Set(b2Vec2(winSize.width/PTM_RATIO,
winSize.height/PTM_RATIO), b2Vec2(winSize.width/PTM_RATIO, 0));
groundBody->CreateFixture(&groundBox, 0);
//创建小球刚体
b2BodyDef spriteBodyDef;
spriteBodyDef.type = b2_dynamicBody;
spriteBodyDef.position.Set(ball1_.position.x/PTM_RATIO,
ball1_.position.y/PTM_RATIO);
spriteBodyDef.userData = ball1_;
// b2Body *spriteBody = _world->CreateBody(&spriteBodyDef);//把小球加入世界
b2CircleShape spriteShape;
spriteShape.m_radius = ball1_.contentSize.width/PTM_RATIO/2;
b2FixtureDef spriteShapeDef;
spriteShapeDef.shape =&spriteShape;
spriteShapeDef.density = 5.0;//密度
spriteShapeDef.isSensor = false;//感知器官,true无法碰撞
spriteShapeDef.restitution = 1.0;
// spriteBody->CreateFixture(&spriteShapeDef);//赋予刚体属性
//小球刚体旋转
CCRotateBy *actionRotate = [CCRotateBy actionWithDuration:1.0];
CCAction *actionRepeatForever = [CCRepeatForever actionWithAction:actionRotate];
[ball1_ runAction:actionRepeatForever];
[self schedule:@selector(tick:)];

这些是init方法里的代码，在代码中注销了两句，为什么不注销小球就不旋转？怎么样让小球看上去在刚体世界里旋转？

Answer 1

你定义好了刚体，然后给他一个力就可以了，不需要给刚体定义动画，这样就一直有外力介入了。你不要定义动画，删除注释，给这个刚体一个力试试看。

追问

可是我想做出来看上去不断旋转的效果，不管刚体受什么力或者不受力，都一直保持匀速旋转，这样如何实现呢？

追答

那就好box2d没关系啊！box2d是创建了这个刚体，让这个刚体在b2World世界里运动，你不需要用box2d的内容，你直接让他runAction就可以了啊！