Sprite Kit 销接头的锚点似乎不正确

Question

我正在使用 Sprite Kit 测试销接头，我发现发生了一些不寻常的事情。

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。我试图让它尽可能简洁：

- (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];
}

我期望的是销接头固定在它们的中心点；但是，当我对此进行测试时，关节的锚点似乎很远。

我是否遗漏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));

把上面改成

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

它应该工作。谢谢斯米克。

SpriteKit: How to create Basic Physics Joints

Answer 2

试试这段代码，我用了你的，遇到了奇怪的问题，所以从头开始。

- (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)];
}