sprite-kit SKNode Collision Simple Sprite Kit project showing collisions, contacts & touch events.


Example

Here is a simple Sprite-Kit GameScene.swift. Create a new, empty SpriteKit project and replace the GameScene.swift with this. Then build and run.

Click on any of the objects on screen to give make them move. Check the logs and the comments to see which ones collide and which ones make contact.

//
//  GameScene.swift
//  bounceTest
//
//  Created by Stephen Ives on 05/04/2016.
//  Copyright (c) 2016 Stephen Ives. All rights reserved.
//

import SpriteKit



class GameScene: SKScene, SKPhysicsContactDelegate {
    
    let objectSize = 150
    let initialImpulse: UInt32 = 300  // Needs to be proportional to objectSize
    
    //Physics categories
    let purpleSquareCategory:   UInt32 = 1 << 0
    let redCircleCategory:      UInt32 = 1 << 1
    let blueSquareCategory:     UInt32 = 1 << 2
    let edgeCategory:           UInt32 = 1 << 31
    
    let purpleSquare = SKSpriteNode()
    let blueSquare = SKSpriteNode()
    let redCircle = SKSpriteNode()
    
    override func didMove(to view: SKView) {
        
        physicsWorld.gravity = CGVector(dx: 0, dy: 0)
        
        //Create an boundary else everything will fly off-screen
        let edge = frame.insetBy(dx: 0, dy: 0)
        physicsBody = SKPhysicsBody(edgeLoopFrom: edge)
        physicsBody?.isDynamic = false  //This won't move
        name = "Screen_edge"
        
        scene?.backgroundColor = SKColor.black
        
        //        Give our 3 objects their attributes
        
        blueSquare.color = SKColor.blue
        blueSquare.size = CGSize(width: objectSize, height: objectSize)
        blueSquare.name = "shape_blueSquare"
        blueSquare.position = CGPoint(x: size.width * -0.25, y: size.height * 0.2)
        
        let circleShape = SKShapeNode(circleOfRadius: CGFloat(objectSize))
        circleShape.fillColor = SKColor.red
        redCircle.texture = view.texture(from: circleShape)
        redCircle.size = CGSize(width: objectSize, height: objectSize)
        redCircle.name = "shape_redCircle"
        redCircle.position = CGPoint(x: size.width * 0.4, y: size.height * -0.4)
        
        purpleSquare.color = SKColor.purple
        purpleSquare.size = CGSize(width: objectSize, height: objectSize)
        purpleSquare.name = "shape_purpleSquare"
        purpleSquare.position = CGPoint(x: size.width * -0.35, y: size.height * 0.4)
        
        addChild(blueSquare)
        addChild(redCircle)
        addChild(purpleSquare)
        
        redCircle.physicsBody = SKPhysicsBody(circleOfRadius: redCircle.size.width/2)
        blueSquare.physicsBody = SKPhysicsBody(rectangleOf: blueSquare.frame.size)
        purpleSquare.physicsBody = SKPhysicsBody(rectangleOf: purpleSquare.frame.size)
        
        setUpCollisions()
        
        checkPhysics()
        
    }
    
    
    func setUpCollisions() {
        
        //Assign our category bit masks to our physics bodies
        purpleSquare.physicsBody?.categoryBitMask = purpleSquareCategory
        redCircle.physicsBody?.categoryBitMask = redCircleCategory
        blueSquare.physicsBody?.categoryBitMask = blueSquareCategory
        physicsBody?.categoryBitMask = edgeCategory  // This is the edge for the scene itself
        
        // Set up the collisions. By default, everything collides with everything.
        
        redCircle.physicsBody?.collisionBitMask &= ~purpleSquareCategory  // Circle doesn't collide with purple square
        purpleSquare.physicsBody?.collisionBitMask = 0   // purpleSquare collides with nothing
        //        purpleSquare.physicsBody?.collisionBitMask |= (redCircleCategory | blueSquareCategory)  // Add collisions with red circle and blue square
        purpleSquare.physicsBody?.collisionBitMask = (redCircleCategory)  // Add collisions with red circle
        blueSquare.physicsBody?.collisionBitMask = (redCircleCategory)  // Add collisions with red circle
        
        
        // Set up the contact notifications. By default, nothing contacts anything.
        redCircle.physicsBody?.contactTestBitMask |= purpleSquareCategory   // Notify when red circle and purple square contact
        blueSquare.physicsBody?.contactTestBitMask |= redCircleCategory     // Notify when blue square and red circle contact
        
        // Make sure everything collides with the screen edge and make everything really 'bouncy'
        enumerateChildNodes(withName: "//shape*") { node, _ in
            node.physicsBody?.collisionBitMask |= self.edgeCategory  //Add edgeCategory to the collision bit mask
            node.physicsBody?.restitution = 0.9 // Nice and bouncy...
            node.physicsBody?.linearDamping = 0.1 // Nice and bouncy...
        }
             
        //Lastly, set ourselves as the contact delegate
        physicsWorld.contactDelegate = self
    }
    
    func didBegin(_ contact: SKPhysicsContact) {
        let contactMask = contact.bodyA.categoryBitMask | contact.bodyB.categoryBitMask
        
        switch contactMask {
        case purpleSquareCategory | blueSquareCategory:
            print("Purple square and Blue square have touched")
        case redCircleCategory | blueSquareCategory:
            print("Red circle and Blue square have touched")
        case redCircleCategory | purpleSquareCategory:
            print("Red circle and purple Square have touched")
        default: print("Unknown contact detected")
        }
    }
    
    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        
        for touch in touches {
            let touchedNode = selectNodeForTouch(touch.location(in: self))
            
            if let node = touchedNode {
                node.physicsBody?.applyImpulse(CGVector(dx: CGFloat(arc4random_uniform(initialImpulse)) - CGFloat(initialImpulse/2), dy: CGFloat(arc4random_uniform(initialImpulse)) - CGFloat(initialImpulse/2)))
                node.physicsBody?.applyTorque(CGFloat(arc4random_uniform(20)) - CGFloat(10))
            }
            
        }
    }
    
    // Return the sprite where the user touched the screen
    func selectNodeForTouch(_ touchLocation: CGPoint) -> SKSpriteNode? {
        
        let touchedNode = self.atPoint(touchLocation)
        print("Touched node is \(touchedNode.name)")
        //        let touchedColor = getPixelColorAtPoint(touchLocation)
        //        print("Touched colour is \(touchedColor)")
        
        if touchedNode is SKSpriteNode {
            return (touchedNode as! SKSpriteNode)
        } else {
            return nil
        }
    }
    
    //MARK: - Analyse the collision/contact set up.
    func checkPhysics() {
        
        // Create an array of all the nodes with physicsBodies
        var physicsNodes = [SKNode]()
        
        //Get all physics bodies
        enumerateChildNodes(withName: "//.") { node, _ in
            if let _ = node.physicsBody {
                physicsNodes.append(node)
            } else {
                print("\(node.name) does not have a physics body so cannot collide or be involved in contacts.")
            }
        }
        
        //For each node, check it's category against every other node's collion and contctTest bit mask
        for node in physicsNodes {
            let category = node.physicsBody!.categoryBitMask
            // Identify the node by its category if the name is blank
            let name = node.name != nil ? node.name! : "Category \(category)"
            
            let collisionMask = node.physicsBody!.collisionBitMask
            let contactMask = node.physicsBody!.contactTestBitMask
            
            // If all bits of the collisonmask set, just say it collides with everything.
            if collisionMask == UInt32.max {
                print("\(name) collides with everything")
            }
            
            for otherNode in physicsNodes {
            if (node.physicsBody?.dynamic == false) {
                print("This node \(name) is not dynamic")
            }
                if (node != otherNode) && (node.physicsBody?.isDynamic == true) {
                    let otherCategory = otherNode.physicsBody!.categoryBitMask
                    // Identify the node by its category if the name is blank
                    let otherName = otherNode.name != nil ? otherNode.name! : "Category \(otherCategory)"
                    
                    // If the collisonmask and category match, they will collide
                    if ((collisionMask & otherCategory) != 0) && (collisionMask != UInt32.max) {
                        print("\(name) collides with \(otherName)")
                    }
                    // If the contactMAsk and category match, they will contact
                    if (contactMask & otherCategory) != 0 {print("\(name) notifies when contacting \(otherName)")}
                }
            }
        }
    }
}