３つ以上のオブジェクトの衝突

タイトル通りでございますが
３つのオブジェクトの衝突について
当方はかなり手こずりましたので、投稿させていただきます。


![contact1 (1).gif](https://qiita-image-store.s3.amazonaws.com/0/55102/ec1f8541-27b9-a7d1-271d-7ac3a751b631.gif)



import SpriteKit

class GameScene: SKScene, SKPhysicsContactDelegate {
    

    let whiteCategory:  UInt32 = 0x1 << 0
    let blackCategory:    UInt32 = 0x1 << 1
    let blueCategory:   UInt32 = 0x1 << 2

    
    override func didMoveToView(view: SKView) {
        

        self.physicsWorld.contactDelegate = self
        
        self.size = view.bounds.size
        self.physicsBody = SKPhysicsBody(edgeLoopFromRect: self.frame)
        self.physicsWorld.gravity = CGVectorMake(0.0, -3.0)
        

        let blackSquare = SKSpriteNode(color: UIColor.blackColor(), size: CGSizeMake(50, 50))
        blackSquare.position = CGPoint(
            x: CGRectGetMidX(self.frame),
            y: CGRectGetMidY(self.frame)
        )
        blackSquare.physicsBody = SKPhysicsBody(rectangleOfSize: CGSizeMake(50, 50))
        blackSquare.physicsBody?.affectedByGravity = false
        blackSquare.physicsBody?.dynamic = false
        

        blackSquare.physicsBody?.categoryBitMask = blackCategory
        blackSquare.physicsBody?.contactTestBitMask = whiteCategory
        

        let blueSquare = SKSpriteNode(color: UIColor.blueColor(), size: CGSizeMake(50, 50))
        blueSquare.position = CGPoint(
            x: CGRectGetMidX(self.frame) - 100,
            y: CGRectGetMidY(self.frame) - 100
        )
        blueSquare.physicsBody = SKPhysicsBody(rectangleOfSize: CGSizeMake(50, 50))
        blueSquare.physicsBody?.affectedByGravity = false
        blueSquare.physicsBody?.dynamic = false
        

//(2)
//        blackSquare.physicsBody?.categoryBitMask = blueCategory
//        blackSquare.physicsBody?.contactTestBitMask = whiteCategory
        
        blueSquare.physicsBody?.categoryBitMask = blueCategory
        blueSquare.physicsBody?.contactTestBitMask = whiteCategory
        

        self.addChild(blackSquare)
        self.addChild(blueSquare)
    }
    
    override func touchesBegan(touches: NSSet, withEvent event: UIEvent) {
        

        for touch in touches {
            
            let location = touch.locationInNode(self)
            let whiteRectangle = SKSpriteNode(color: UIColor.whiteColor(), size: CGSizeMake(50, 50))
            whiteRectangle.position = location
            whiteRectangle.physicsBody = SKPhysicsBody(rectangleOfSize: CGSizeMake(50, 50))
            

            whiteRectangle.physicsBody?.categoryBitMask = whiteCategory
   //         whiteRectangle.physicsBody?.contactTestBitMask = blackCategory
    //        whiteRectangle.physicsBody?.contactTestBitMask = blueCategory
            
            self.addChild(whiteRectangle)
        }
        
    }
    
    override func update(currentTime: CFTimeInterval) {
    }
    

    func didBeginContact(contact: SKPhysicsContact!) {
        
        var firstBody, secondBody: SKPhysicsBody
        

        if contact.bodyA.categoryBitMask < contact.bodyB.categoryBitMask {
            firstBody = contact.bodyA
            secondBody = contact.bodyB
            //thirdBody = contact.bodyB
        } else {
            firstBody = contact.bodyB
            secondBody = contact.bodyA
           // thirdBody = contact.bodyA
        }
        

        if firstBody.categoryBitMask & whiteCategory != 0 &&
            secondBody.categoryBitMask & blackCategory != 0 {
                //secondBody.node?.removeFromParent()
                println("black")
        }
        

        if firstBody.categoryBitMask & whiteCategory != 0 &&
            secondBody.categoryBitMask & blueCategory != 0 {
                //secondBody.node?.removeFromParent()
                println("blue")
        }
    }
}