How to create a ring with 3D effect using Sprite Kit?

Question

I want to create a ring with a 3D effect using Sprite Kit. (SEE IMAGES)

I tried subclassing a SKNode and adding two nodes as children. (SEE CODE)

One node was a complete SKShapeNode ellipse, and the other was half ellipse using SKCropNode with a higher zPosition.

It looks good, but the SKCropNode increases the app CPU usage from 40% to 99%.

Any ideas on how to reduce the SKCropNode performance cost, or any alternative to create the same ring 3D effect?

class RingNode: SKNode {

    let size: CGSize

    init(size: CGSize, color: SKColor)
    {
        self.size = size
        self.color = color

        super.init()

        ringPartsSetup()
    }

    private func ringPartsSetup() {

        // LEFT PART (half ellipse)
        let ellipseNodeLeft = getEllipseNode()
        let leftMask = SKSpriteNode(texture: nil, color: SKColor.blackColor(), size: CGSize(
            width: ellipseNodeLeft.frame.size.width/2,
            height: ellipseNodeLeft.frame.size.height))
        leftMask.anchorPoint = CGPoint(x: 0, y: 0.5)
        leftMask.position = CGPoint(x: -ellipseNodeLeft.frame.size.width/2, y: 0)
        let leftNode = SKCropNode()
        leftNode.addChild(ellipseNodeLeft)
        leftNode.maskNode = leftMask
        leftNode.zPosition = 10 // Higher zPosition for 3D effect
        leftNode.position = CGPoint(x: -leftNode.frame.size.width/4, y: 0)
        addChild(leftNode)

        // RIGHT PART (complete ellipse)
        let rightNode = getEllipseNode()
        rightNode.position = CGPoint(x: 0, y: 0)
        rightNode.zPosition = 5
        addChild(rightNode)
    }

    private func getEllipseNode() -> SKShapeNode {
        let ellipseNode = SKShapeNode(ellipseOfSize: CGSize(
            width: size.width,
            height: size.height))
        ellipseNode.strokeColor = SKColor.blackColor()
        ellipseNode.lineWidth = 5
        return ellipseNode
    }    
}

Answer 1

You've got the right idea with your two-layer approach and the half-slips on top. But instead of using a shape node inside a crop node, why not just use a shape node whose path is a half-ellipse? Create one using either CGPath or UIBezierPath API — use a circular arc with a transform to make it elliptical — then create your SKShapeNode from that path.

Answer 2

You may try converting your SKShapeNode to an SKSpriteNode. You can use SKView textureFromNode: (but we aware of issues with scale that require you to use it only after the node has been added to the view and at least one update cycle has run), or from scratch using an image (created programatically with a CGBitmapContext, of course).