SKPhysicsJointFixed doesn't keep nodes together while moving one

问题

I've created 2 SKSpriteNodes, and connected them by a SKPhysicsJointFixed, to keep them stuck together. The problem is when I apply a SKAction.move(by:, duration:) to the first, it moves alone. why is that, and how can I move them together? I've searched a lot, but can't seem to find any new or useful information. Please help. Thanks in advance.

Here's the code:

import SpriteKit

class myGame: SKScene {

var node1: SKSpriteNode!
var node2: SKSpriteNode!

func createNode(_ position: CGPoint, color: UIColor) -> SKSpriteNode {
    let node = SKSpriteNode(color: color, size: CGSize(width: 50, height: 50))
    node.position = position
    node.physicsBody = SKPhysicsBody(rectangleOf: node.size, center: position)
    node.physicsBody?.affectedByGravity = false
    node.physicsBody?.allowsRotation = false
    return node
}

func setup() {
    node1 = createNode(.zero, color: .red)
    node2 = createNode(CGPoint(x: 0, y: -50), color: .green)
    self.addChild(node1)
    self.addChild(node2)

    let anchor = CGPoint(x: node1.size.width/2, y: -node1.size.height/2)
    let joint = SKPhysicsJointFixed.joint(withBodyA: node1.physicsBody!, bodyB: node2.physicsBody!, anchor: anchor)
    physicsWorld.add(joint)

}

override func didMove(to view: SKView) {
    setup()
}

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    node1.run(SKAction.move(by: CGVector(dx: 0, dy: 100), duration: 2))
}


}

回答1:

This is very strange indeed, but I have encountered similar things before. Its the AllowRotation on the physicsBody that creates the problem.

fix:

node.physicsBody?.allowsRotation = true

Note: your physics body for the second node is a bit off. I suggest you do like this instead:

node.physicsBody = SKPhysicsBody(rectangleOf: node.size)

And your joint is currently in the right corner of the nodes, Fix:

let anchor = CGPoint(x: 0, y: -node1.size.height/2)

unless you want it to be like that ofc :)

One last tip if you don't already know it. set showPhysics in your gameViewController to see an outline of your physics bodies. it does help a lot when working with physics.

view.showsPhysics = true

来源：https://stackoverflow.com/questions/45174110/skphysicsjointfixed-doesnt-keep-nodes-together-while-moving-one

标签

swift

sprite-kit

skphysicsjoint