SKSceneWithUserInteractionBugfix.swift

//
// Original Objective C version: https://gist.github.com/bobmoff/7110052
//
// Fix SpriteKit's SKNode bug on iOS 7 & 8: nodes capture touch events
// even when userInteractionEnabled is false and the nodes are hidden.
//
// Details:
// http://stackoverflow.com/questions/19511334/sprite-with-userinteractionenabled-set-to-yes-does-not-receive-touches-when-cove
//
// How to use:
// Use SKSceneWithUserInteractionBugfix class in place of SKScene.
//

import SpriteKit

extension SKNode {
    func nodeDepthPriority() -> String {
        var code = ""
        var currentNode = self
        while let parent = currentNode.parent {
            var idx = 0
            for obj in parent.children {
                if obj == currentNode {
                    code = NSString(format: "%03d%@", idx, code) as String
                    break
                }
                ++idx
            }
            currentNode = parent
        }
        return code
    }
}

extension SKScene {
    func nodeWithHighestPriority(touches: NSSet) -> SKNode? {
        // Only allow touches to be receieved by nodes with userInteractionEnabled, and only the one with the highest touch priority
        guard let touch = touches.anyObject() else { return nil }
        let touchLocation = touch.locationInNode(self)
        let touchedNodes = nodesAtPoint(touchLocation)
        var nodeToTouch: SKNode!
        for node in touchedNodes {
            if node.userInteractionEnabled && !node.hidden && node.alpha > 0 {
                if nodeToTouch == nil {
                    nodeToTouch = node
                } else if node.parent == nodeToTouch.parent && node.zPosition > nodeToTouch.zPosition {
                    nodeToTouch = node
                } else if node.parent == nodeToTouch.parent && node.zPosition == nodeToTouch.zPosition && nodeToTouch.nodeDepthPriority().compare(node.nodeDepthPriority()) == .OrderedAscending {
                    nodeToTouch = node
                } else if node.parent != nodeToTouch.parent && nodeToTouch.nodeDepthPriority().compare(node.nodeDepthPriority()) == .OrderedAscending {
                    nodeToTouch = node
                }
            }
        }
        return nodeToTouch
    }
}

public class SKSceneWithUserInteractionBugfix: SKScene {
    public override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
        let nodeToTouch = nodeWithHighestPriority(touches)
        nodeToTouch?.touchesBegan(touches, withEvent: event)
    }
    
    public override func touchesEnded(touches: Set<UITouch>, withEvent event: UIEvent?) {
        let nodeToTouch = nodeWithHighestPriority(touches)
        nodeToTouch?.touchesEnded(touches, withEvent: event)
    }
    
    public override func touchesCancelled(touches: Set<UITouch>?, withEvent event: UIEvent?) {
        guard let touches = touches else { return }
        let nodeToTouch = nodeWithHighestPriority(touches)
        nodeToTouch?.touchesCancelled(touches, withEvent: event)
    }
}