objective-c – SpriteKit：如何创建基础物理接头

我试图在两个SK物理机构之间创建简单的关节.但是,他们是奇怪的.
我很清楚锚点应该在场景坐标上.请看附件源代码.

例如,这是在矩形上附加一个小方块之后如何得到固定的关节.

-(void)createFixedJointOnScene:(SKScene*)scene

{

//Adding Rectangle

    SKSpriteNode* BACkBone = [[SKSpriteNode alloc] initWithColor:[UIColor whiteColor] size:CGSizeMake(20,200)];
BACkBone.position = CGPointMake(CGRectGetWidth(self.framE)/2.0,CGRectGetHeight(self.framE)/2.0);
BACkBone.physicsBody = [SKPhysicsBody bodyWithRectangLeofSize:BACkBone.size];
BACkBone.physicsBody.categoryBitMask = GFPhysicsCategoryRectangle;
BACkBone.physicsBody.collisionBitMask = GFPhysicsCategoryWorld;
[scene addChild:BACkBone];

//Adding Square
SKSpriteNode* head = [[SKSpriteNode alloc] initWithColor:[SKColor grayColor] size:CGSizeMake(40,40)];
head.physicsBody = [SKPhysicsBody bodyWithRectangLeofSize:head.size];
head.position = CGPointMake(BACkBone.position.x,BACkBone.position.y-40);
head.physicsBody.categoryBitMask = GFPhysicsCategorySquare;
head.physicsBody.collisionBitMask = GFPhysicsCategoryWorld;
[scene addChild:head];

//Pinning Rectangle and Square
NSLog(@"Head position %@",NSStringFromCGPoint(head.position));
SKPhysicsJointFixed* pin =[SKPhysicsJointFixed jointWithBodyA:BACkBone.physicsBody bodyB:head.physicsBody anchor:head.position];
[self.physicsWorld addJoint:pin];

}

https://dl.dropboxusercontent.com/u/62559842/PhysicsTest.zip

谢谢.

head.physicsBody = [SKPhysicsBody bodyWithRectangLeofSize:head.size];
head.position = CGPointMake(BACkBone.position.x,BACkBone.position.y-40);

head.position = CGPointMake(BACkBone.position.x,BACkBone.position.y-40);
head.physicsBody = [SKPhysicsBody bodyWithRectangLeofSize:head.size];