CODEWITHSUNDEEP
iossprite-kitskshapenodeskphysicsjoint
Lee Probert
Lee Probert

Reputation: 10859

SpriteKit add a spring joint to each node

I am using SpriteKit to create a fun Hotspot UI for a project. It should be really simple! Just a background image with a load of dots on it. When you tap on a dot it scales up. When you tap again it returns to its normal size and position. But, more importantly, each dot has physics, so when it scales up, the others move aside temporarily. When the dots return to their normal scale they will spring back into position.

To achieve this I have a bunch of SKShapeNodes positioned on the page. I am also creating an SKPhysicsJointSpring that is attached to the scenes physicsBody and the SKShapeNode.

Here's the code for the scene:

override func didMoveToView(view: SKView) {

    name = "Hotspot test"
    physicsWorld.gravity = CGVectorMake(0, 0)

    let physicsBody = SKPhysicsBody(edgeLoopFromRect: self.frame)
    self.physicsBody = physicsBody


    for i in 1...10 {

        let j:__uint32_t = 0x1 << UInt32(i) // <- IGNORE THIS. IRRELEVANT
        let shape = DotNode(circleOfRadius: 60, name: "Ball"+String(i), id: i, bitmask: j)

        // Position objects in a circle around the center
        let degrees = (360/10)*i
        let radians = degrees.degreesToRadians
        let radius = CGFloat(300)
        let cosR = cos(radians)
        let sinR = sin(radians)
        let xPos = radius*cosR+frame.size.width/2
        let yPos = radius*sinR+frame.size.height/2

        let pos = CGPoint(x: xPos, y: yPos)
        shape.position = pos

        addChild(shape)

        let spring = SKPhysicsJointSpring.jointWithBodyA(self.physicsBody!, bodyB: shape.physicsBody!, anchorA: pos, anchorB: pos)
        spring.damping = 0.01
        physicsWorld.addJoint(spring)
    }

DotNode is the SKShapeNode subclass. This is what it looks like on-screen:

nodes static

and this is what it looks like when they scale-up:

enter image description here

See the problem right? They don't interact with each other now. I can see the Spring joint is attached when I drag one of them:

enter image description here

Is there any reason why the objects no longer interact with each other?

This is what happens if you just remove the joint:

enter image description here

The objects push each other around. This must be achievable. What am I doing wrong?

Upvotes: 1

Views: 847

Answers (1)

Lee Probert
Lee Probert

Reputation: 10859

Sadly, it seems that this is not possible with SpriteKit. This post: SKPhysicsJoint: Contacts and collisions not working confirms it.

I have to say, this seems crazy. Why would you not want to create joints and springs and then have the nodes you have connected collide and react in the physics world?

It seems I will have to lose the spring and just code the nodes to constantly drift back to their original location. That way, when one of them scales and pushes the others out of the way, they will always try and get home.

Upvotes: 1

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