I'm creating a motocross game where I have a curved ground on which the player should drive. My code for creating the ground looks like this:
let path = UIBezierPath()
let startPoint = CGPoint(x: 0.0, y: self.playerCamera.position.x + 50)
let endPoint = CGPoint(x: self.frame.width, y: self.playerCamera.position.x + 50)
path.addCurveToPoint(endPoint, controlPoint1: CGPoint(x: 200.0, y: 100), controlPoint2: CGPoint(x: 400.0, y: -100))
let myShape = SKShapeNode()
myShape.path = path.CGPath
myShape.lineWidth = 20
myShape.physicsBody = SKPhysicsBody(edgeLoopFromPath: path.CGPath)
myShape.physicsBody?.categoryBitMask = CollisionCategories.Ground
myShape.physicsBody?.contactTestBitMask = CollisionCategories.Player
myShape.physicsBody?.dynamic = false
myShape.physicsBody?.affectedByGravity = false
myShape.physicsBody?.allowsRotation = false
I think it is impossible to do it without the assistance of a tool.
Please have a look at this: http://avionicsdev.esy.es/article.php?id=13&page=1
You can use this tool to achieve the desired effect:
"This tool will let us draw a path and then returns code that will help us draw that path into Xcode" (excerpt from the first link)
You may have to screen cap your UIBezierPath and convert it to a Sprite, but I am not certain it is necessary. Have a look at the explanations of the tool.
Change Game Engine.
In my opinion, you might be able to find a way to achieve what you want, but it won't be a simple and straightforward solution. On the other hand, other game engines are more complete and should provide you all you need without having to use "tricks" to achieve what you want.
I hope I am wrong and SpriteKit is indeed more complete than that, but it doesn't look like it.
Use Unity instead of SpriteKit.
SpriteKit is great for relatively simple games, but it has certain limitations and you just found one it seems.
Unity is a full fledged Game Engine which should better suit your needs.
Or have a look at Cocos2D: http://cocos2d.spritebuilder.com/ if you want to keep using Swift (You might have to learn C# to use Unity).