Swift SpriteKit Mario style rotating platform that stays horizontal

Question

I am trying to create a mario style rotating platform that stays horizontal.

What I have done so far is create a simple class for this for testing purposes.

  class PlatformRound: SKNode {

    let platform: Platform

// MARK: - Init
init(barSize: CGSize, color: SKColor, pos: CGPoint) {

    /// Base
    let base = SKShapeNode(circleOfRadius: 6)
    //base.name = Platform.Name.normal
    base.fillColor = SKColor.darkGrayColor()
    base.strokeColor = base.fillColor
    base.position = pos
    let rotatingAction = SKAction.rotateByAngle(CGFloat(-M_PI), duration: 8)
    base.runAction(SKAction.repeatActionForever(rotatingAction))

    /// Bar
    let bar = Platform(size: barSize, color: color, pos: CGPointMake(0, 0 - (barSize.height / 2)), ofType: .Normal) 
    bar.zPosition = -200

    /// Platform that supposed to stay horizontal
    let platformSize = CGSizeMake(40, GameplayConfig.World.platformHeight)
    let platformPos = CGPointMake(0, 0 - (bar.size.height / 2))
    platform = Platform(size: platformSize, color: color, pos: platformPos, ofType: .Normal)

    super.init()

    addChild(base)
    base.addChild(bar)
    bar.addChild(platform)
}

required init?(coder aDecoder: NSCoder) {
    fatalError("init(coder:) has not been implemented")
   }
}

I am creating a roundBase that I can rotate. I than create a bar that goes down from the base, that is added to the base node. Finally I create the platform that is supposed to stay horizontal at all times. I am using another Platform subclass to create the bar and platform, but they are not relevant to this question.

How can I make the platform stay horizontal. I tried the following which didnt work.

1) In update in my gameScene I constantly update the platform position or zRotation

 platformRound.platform.zRotation = ...

2) Create a zRotation property that gets set once the platform is added and than use that property to constantly update the zRotation.

3) Tried playing around with physicsJoints

Im sure there is a easy way that I am missing. I would appreciate any help.

Are you talking about this https://www.youtube.com/watch?v=Igjf-W87bW4 or ? — Whirlwind, Apr 14 '16 at 13:39
Hey, thanks for the reply. Thats exactly what I'm talking about. — crashoverride777, Apr 14 '16 at 13:41
This should be *easy*. Still, It would be helpful if you add the part of the code where you create instance of PlatformRound and the code where you rotate it around circumference (if you doing it like that at all?). Or I can make you an simple example with `SKSpriteNodes`, but you might have to modify it to fit into your current setup. — Whirlwind, Apr 14 '16 at 13:45
Yeah I was just experimenting with the subclass. I would have probably made it a subclass of SKSpriteNode anyway so anything you suggest is great. I dont think the code in gameScene is relevant as I am simply adding it to the scene. The rotating base code is in platformRound, I am rotating the base with an SKAction. It all works I just cannot get the platform to stay horizontal. — crashoverride777, Apr 14 '16 at 13:48
Okay, will show you how would I do it as soon as possible ... — Whirlwind, Apr 14 '16 at 13:50
Thank you very much, works great. I was just playing around to make it into a subclass. Thanks again — crashoverride777, Apr 14 '16 at 14:59

Whirlwind · Accepted Answer · 2016-04-14T14:42:45.397

This should work:

class GameScene: SKScene{

    override func didMoveToView(view: SKView) {

        backgroundColor = .blackColor()

        let centerSprite = SKSpriteNode(color: .whiteColor(), size: CGSize(width: 10, height: 10))

        centerSprite.zPosition = 3

        let platform = SKSpriteNode(color: .orangeColor(), size: CGSize(width: 70, height: 20))
        platform.zPosition = 2
        platform.name = "platform"

        let container = SKNode()
        container.position = CGPoint(x: frame.midX, y: frame.midY)

        container.addChild(centerSprite) //Just for debugging
        container.addChild(platform)
        let radius = 120

        let chain = SKSpriteNode(color: .grayColor(), size: CGSize(width: 3, height: radius))
        chain.position = CGPoint(x: 0, y: radius/2)
        container.addChild(chain)


        platform.position = CGPoint(x: 0, y: radius)

        let rotatingAction = SKAction.rotateByAngle(CGFloat(-M_PI), duration: 8)
        container.runAction(SKAction.repeatActionForever(rotatingAction), withKey: "rotating")

        addChild(container)

    }

    override func didEvaluateActions() {

        self.enumerateChildNodesWithName("//platform") { node,stop in

            if let parent = node.parent{
                node.zRotation = -parent.zRotation
            }
        }
    }
}

What I did, is that I have added platform node into container node and applied rotation to that container. Later on, in didEvaluateActions I've adjusted the rotation of platform (to have a negative value of its parent's zRotation). And that's it.

Here is the result of what I am seeing:

The adjusting is needed, because otherwise the platform will end-up rotating along with its parent (notice how white, center sprite is being rotated along with container node).

Swift SpriteKit Mario style rotating platform that stays horizontal

1 Answers1