Give an SKNode its own physics - swift

Question

Is there a way to give an SKNode its own physics? I have an SKShapeNode call "backGround" which I use for the parent node of most of my other nodes. I am constantly moving "background" to the left, to give the illusion that the player is moving forward. However, one of the objects that has "backGround" as a parent node is a pin with a rope hanging from it. When background accelerates to the left, is there a way to make it so the rope doesn't swing back and forth, as ropes tend to do when accelerating or decelerating?
EDIT: Here is my code:
func createRopeNode(pos: CGPoint) -> SKSpriteNode{
let ropeNode = SKSpriteNode(imageNamed: "Ball")
ropeNode.size = CGSize(width: 5, height: 5)
ropeNode.physicsBody = SKPhysicsBody(rectangleOfSize: ropeNode.size)
ropeNode.physicsBody?.affectedByGravity = true
ropeNode.physicsBody?.collisionBitMask = 0
ropeNode.alpha = 1
ropeNode.position = CGPoint(x: pos.x + 0, y: pos.y)
ropeNode.name = "RopePiece"
let text = SKSpriteNode(imageNamed: "RopeTexture")
ropeNode.zPosition = -5
text.runAction(SKAction.rotateByAngle(atan2(-dx!, dy!), duration: 0))
ropeNode.addChild(text)
return ropeNode
}
override func touchesBegan(touches: Set<NSObject>, withEvent event: UIEvent) {
/* Called when a touch begins */
if (!playerIsConnected){
playerIsConnected = true
for touch in (touches as! Set<UITouch>) {
let location = touch.locationInNode(self)
dx = pin.position.x - playerPoint!.x
dy = pin.position.y - playerPoint!.y
let length = sqrt(pow(dx!, 2) + pow(dy!, 2))
let distanceBetweenRopeNodes = 5
let numberOfPieces = Int(length)/distanceBetweenRopeNodes
var ropeNodes = [SKSpriteNode]()
//adds the pieces to the array at respective locations
for var index = 0; index < numberOfPieces; ++index{
let point = CGPoint(x: pin.position.x + CGFloat((index) * distanceBetweenRopeNodes) * sin(atan2(dy!, -dx!) + 1.5707), y: pin.position.y + CGFloat((index) * distanceBetweenRopeNodes) * cos(atan2(dy!, -dx!) + 1.5707))
let piece = createRopeNode(point)
ropeNodes.append(piece)
world.addChild(ropeNodes[index])
}
let firstJoint = SKPhysicsJointPin.jointWithBodyA(ropeNodes[0].physicsBody, bodyB: pin.physicsBody, anchor:
CGPoint(x: (ropeNodes[0].position.x + pin.position.x)/2, y: (ropeNodes[0].position.y + pin.position.y)/2))
firstJoint.frictionTorque = 1
self.physicsWorld.addJoint(firstJoint)
for var i = 1; i < ropeNodes.count; ++i{
let nodeA = ropeNodes[i - 1]
let nodeB = ropeNodes[i]
let middlePoint = CGPoint(x: (nodeA.position.x + nodeB.position.x)/2, y: (nodeA.position.y + nodeB.position.y)/2)
let joint = SKPhysicsJointPin.jointWithBodyA(nodeA.physicsBody, bodyB: nodeB.physicsBody, anchor: middlePoint)
joint.frictionTorque = 0.1
self.physicsWorld.addJoint(joint)
}
finalJoint?.frictionTorque = 1
finalJoint = SKPhysicsJointPin.jointWithBodyA(ropeNodes[ropeNodes.count - 1].physicsBody, bodyB: player.physicsBody, anchor:
CGPoint(x: (ropeNodes[ropeNodes.count - 1].position.x + playerPoint!.x)/2, y: (ropeNodes[ropeNodes.count - 1].position.y + playerPoint!.y)/2))
self.physicsWorld.addJoint(finalJoint!)
}
}
else{
physicsWorld.removeJoint(finalJoint!)
playerIsConnected = false
}
}

Answer 1

Anchor points are what you are looking for. Move the anchor point of the scene to only move the "camera" of the scene (what is displayed onscreen). This will not jostle the pin and rope. Keep in mind that the anchor point is on a slightly different scale from the scene.
Where the width of the scene could be 1024, the "width" of the of the anchor point for one scene length is 1 (basically counting as one width of the node). Same for the height, where it could be 768, the "height" would still be 1 in the anchor point coordinate space. So to move half a screen width, move the anchor point 0.5
The anchor point is a CGPoint, so you can go vertically as well. Here's a quick example:
var xValue : Float = 0.75
var yValue : Float = 0.0
self.scene?.anchorPoint = CGPointMake(xValue, yValue);
And for further reading, here's a link to the documentation on anchor points for sprites.