使 SKPhysicsBody 单向

Question

我有一个SKSpriteNode 作为一个球，它被赋予了所有SKPhysicsBody 属性在各个方向移动。我现在想要的是让它unidirectional （只朝它之前没有移动过的方向移动，而不是回到它曾经移动过的路径）。目前我对这个问题有以下想法，

• 创建一个fieldBitMask，到被它迭代的路径并排斥 球不回去
• 通过touchesBegan/ touchesMoved 方法在球上应用某种force/ impulses 以防止它返回
• 可以在update 方法中处理的东西
• 来自 stackflowoverflow 的救星，他甚至在周末都在编码 :)

支持代码 sn-ps 以便更好地理解，

//getting current touch position by using UIEvent methods
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        guard let touch = touches.first else {return}
        let location = touch.location(in: self)
        lastTouchPoint = location
    }
    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
        guard let touch = touches.first else {return}
        let location = touch.location(in: self)
        lastTouchPoint = location
    }
    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
        lastTouchPoint = nil
    }
    override func touchesCancelled(_ touches: Set<UITouch>, with event: UIEvent?) {
        lastTouchPoint = nil
    }

//ball created
    func createPlayer(){
        player = SKSpriteNode(imageNamed: "player")
        player.position = CGPoint(x: 220, y: 420)
        player.zPosition = 1

    //physics for ball
    player.physicsBody = SKPhysicsBody(circleOfRadius: player.size.width / 2)
    player.physicsBody?.allowsRotation = false
    player.physicsBody?.linearDamping =  0.5


    player.physicsBody?.categoryBitMask = collisionTypes.player.rawValue
    player.physicsBody?.contactTestBitMask = collisionTypes.finish.rawValue
    player.physicsBody?.collisionBitMask = collisionTypes.wall.rawValue

    addChild(player)
}

//unwarp the optional property, calclulate the postion between player touch and current ball position
override func update(_ currentTime: TimeInterval) {
    guard isGameOver == false else { return }
    if let lastTouchPosition = lastTouchPoint {
        //this usually gives a large value (related to screen size of the device) so /100 to normalize it
        let diff = CGPoint(x: lastTouchPosition.x - player.position.x, y: lastTouchPosition.y - player.position.y)
        physicsWorld.gravity = CGVector(dx: diff.x/100, dy: diff.y/100)
    }
}

Answer 1

这是touchesBegan/ touchesMoved 和update func 中的小技巧组合，

首先您需要了解发生了哪个触摸，获取它的名称（在我的 情况下，我制作了 alpha 为 0 的节点，但在 移动它们，即 alpha 1)。在touchesBegan, touchesMoved如下

                        guard let touch = touches.first else {return}
                        let location = touch.location(in: self)
                        lastTouchPoint = location

                        let positionInScene = touch.location(in: self)
                        let touchedNode = self.atPoint(positionInScene)

                        if let name = touchedNode.name
                        {
                            if name == "vortex"
                            {
                                touching = false
                                self.view!.isUserInteractionEnabled = false
                                print("Touched on the interacted node")
                            }else{
                                self.view!.isUserInteractionEnabled = true
                                touching = true
                            }
                        }
                    }

第二次使用BOOL touching 来跟踪用户交互，在屏幕上使用获取点击识别器设置，如下所示

func setupTapDetection() {
        let t = UITapGestureRecognizer(target: self, action: #selector(tapped(_:)))
        view?.addGestureRecognizer(t)
    }

@objc func tapped(_ tap: UITapGestureRecognizer) {
        touching = true
    }

最后在update进行如下检查，

        guard isGameOver == false else { return }
        self.view!.isUserInteractionEnabled = true

        if(touching ?? true){
            if let lastTouchPosition = lastTouchPoint {
                //this usually gives a large value (related to screen size of the device) so /100 to normalize it
                let diff = CGPoint(x: lastTouchPosition.x - player.position.x, y: lastTouchPosition.y - player.position.y)
                physicsWorld.gravity = CGVector(dx: diff.x/100, dy: diff.y/100)
            }
        }
    }