雪碧套件针脚关节似乎有一个不正确的锚点

Question

我正在测试与雪碧套件针关节，我发现一些不寻常的事情发生。

我想要的设置是这样的：一个宽的扁平盒子和两个圆圈;圆圈通过SKPhysicsPinJoints连接到盒子，因此它们可以充当轮子。

这是我的代码。我试图尽可能简洁：

- (SKNode*) createWheelWithRadius:(float)wheelRadius { 
    CGRect wheelRect = CGRectMake(-wheelRadius, -wheelRadius, wheelRadius*2, wheelRadius*2); 

    SKShapeNode* wheelNode = [[SKShapeNode alloc] init]; 
    wheelNode.path = [UIBezierPath bezierPathWithOvalInRect:wheelRect].CGPath; 

    wheelNode.physicsBody = [SKPhysicsBody bodyWithCircleOfRadius:wheelRadius]; 

    return wheelNode; 
} 


- (void) createCar { 

    // Create the car 
    SKSpriteNode* carNode = [SKSpriteNode spriteNodeWithColor:[SKColor yellowColor] size:CGSizeMake(150, 50)]; 
    carNode.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:carNode.size]; 
    carNode.position = CGPointMake(CGRectGetMidX(self.frame), CGRectGetMidY(self.frame)); 
    [self addChild:carNode]; 

    // Create the left wheel 
    SKNode* leftWheelNode = [self createWheelWithRadius:30]; 
    leftWheelNode.position = CGPointMake(carNode.position.x-80, carNode.position.y); 
    [self addChild:leftWheelNode]; 

    // Create the right wheel 
    SKNode* rightWheelNode = [self createWheelWithRadius:30]; 
    rightWheelNode.position = CGPointMake(carNode.position.x+80, carNode.position.y); 
    [self addChild:rightWheelNode]; 

    // Attach the wheels to the body 
    CGPoint leftWheelPosition = leftWheelNode.position; 
    CGPoint rightWheelPosition = rightWheelNode.position; 

    SKPhysicsJointPin* leftPinJoint = [SKPhysicsJointPin jointWithBodyA:carNode.physicsBody bodyB:leftWheelNode.physicsBody anchor:leftWheelPosition]; 
    SKPhysicsJointPin* rightPinJoint = [SKPhysicsJointPin jointWithBodyA:carNode.physicsBody bodyB:rightWheelNode.physicsBody anchor:rightWheelPosition]; 

    [self.physicsWorld addJoint:leftPinJoint]; 
    [self.physicsWorld addJoint:rightPinJoint]; 
} 

我期待的是，销接头固定在它们的中心点;然而，当我测试这个时，关节的锚点似乎很遥远。

我是否错过了一些非常明显的东西？

Answer 1

我也有这个问题，原因是在设置精灵位置之前设置物理体。

carNode.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:carNode.size]; 
carNode.position = CGPointMake(CGRectGetMidX(self.frame), CGRectGetMidY(self.frame)); 

更改上面

carNode.position = CGPointMake(CGRectGetMidX(self.frame), CGRectGetMidY(self.frame)); 
carNode.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:carNode.size]; 

它应该工作。感谢Smick。

SpriteKit: How to create Basic Physics Joints

Answer 2

试试这段代码，我使用过你的代码，发现了奇怪的问题，所以从零开始。

- (SKShapeNode*) makeWheel 
{ 
    SKShapeNode *wheel = [[SKShapeNode alloc] init]; 
    CGMutablePathRef myPath = CGPathCreateMutable(); 
    CGPathAddArc(myPath, NULL, 0,0, 16, 0, M_PI*2, YES); 
    wheel.path = myPath; 
    return wheel; 
} 


- (void) createCar 
{ 

    self.physicsBody = [SKPhysicsBody bodyWithEdgeLoopFromRect:CGRectMake(0, 0, self.size.width, self.size.height)]; 

    // 1. car body 
    SKSpriteNode *carBody = [SKSpriteNode spriteNodeWithColor:[UIColor whiteColor] size:CGSizeMake(120, 8)]; 
    carBody.position = CGPointMake(200, 200); 
    carBody.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:carBody.size]; 
    [self addChild:carBody]; 

    // 2. wheels 
    SKShapeNode *leftWheel = [self makeWheel]; 
    leftWheel.position = CGPointMake(carBody.position.x - carBody.size.width/2, carBody.position.y); 
    leftWheel.physicsBody = [SKPhysicsBody bodyWithCircleOfRadius:16]; 
    [self addChild:leftWheel]; 

    SKShapeNode *rightWheel = [self makeWheel]; 
    rightWheel.position = CGPointMake(carBody.position.x + carBody.size.width/2, carBody.position.y); 
    rightWheel.physicsBody = [SKPhysicsBody bodyWithCircleOfRadius:16]; 
    [self addChild:rightWheel]; 

    // 3. Join wheels to car 
    [self.physicsWorld addJoint:[SKPhysicsJointPin jointWithBodyA:carBody.physicsBody bodyB:leftWheel.physicsBody anchor:leftWheel.position]]; 
    [self.physicsWorld addJoint:[SKPhysicsJointPin jointWithBodyA:carBody.physicsBody bodyB:rightWheel.physicsBody anchor:rightWheel.position]]; 

    // 4. drive car 
    [carBody.physicsBody applyForce:CGVectorMake(10, 0)]; 
}