前兩天介紹了CAShapeLayer及動畫，那麼今天來做個貪吃蛇小遊戲。

首先看一下貪食蛇遊戲的畫面

貪食蛇頭、身體和吃蘋果的運作

如何蛇的頭可以一步一步往前跑，首先我們先創出蛇頭，並讓它賦予可以隨著手勢滑動而更改方向

//蛇的頭
func circleView(height:CGFloat,width:CGFloat){
    snakePoint.append(UIView())
    snakePoint[0] = UIView.init(frame: CGRect.init(x: 0, y: 0, width: 10, height: 10))
    snakePoint[0].center = CGPoint(x: width/2, y: height/2)
    snakePoint[0].backgroundColor = #colorLiteral(red: 0.3411764801, green: 0.6235294342, blue: 0.1686274558, alpha: 1)
    snakePoint[0].layer.cornerRadius = snakePoint[0].frame.width/2      //以下兩行讓蛇的頭變成圓形
    snakePoint[0].clipsToBounds = true
    self.mainView.secondView.addSubview(snakePoint[0])
    //down
    let swipeDown = UISwipeGestureRecognizer(target: self, action: #selector(swipeAction))
    swipeDown.direction = .down
    swipeDown.numberOfTouchesRequired = 1
    mainView.addGestureRecognizer(swipeDown)
    //left
    let swipeLeft = UISwipeGestureRecognizer(target: self, action: #selector(swipeAction))
    swipeLeft.direction = .left
    swipeLeft.numberOfTouchesRequired = 1
    mainView.addGestureRecognizer(swipeLeft)
    //right
    let swipeRight = UISwipeGestureRecognizer(target: self, action: #selector(swipeAction))
    swipeRight.direction = .right
    swipeRight.numberOfTouchesRequired = 1
    mainView.addGestureRecognizer(swipeRight)
    //up
    let swipeUp = UISwipeGestureRecognizer(target: self, action: #selector(swipeAction))
    swipeUp.direction = .up
    swipeUp.numberOfTouchesRequired = 1
    mainView.addGestureRecognizer(swipeUp)
}

再來加上滑動的方法，必須加上判斷以防同時往一個方向滑兩次以上，會造成頭一次跳兩格以上

//滑動func
@objc func swipeAction(recognizer:UISwipeGestureRecognizer){
    let directions = recognizer.direction
    if directions == .left && nowDirection != .right{
        nowDirection = directions
    }else if directions == .right && nowDirection != .left{
        nowDirection = directions
    }else if directions == .up && nowDirection != .down{
        nowDirection = directions
    }else if directions == .down && nowDirection != .up{
        nowDirection = directions
    }
}

再來我們先固定蛇頭原始的方向，先在全域變數加上這行
var nowDirection:UISwipeGestureRecognizerDirection = .left

再加上一個Timer讓頭可以一直往下個座標移動
var timer:Timer?

然後在viewDidLoad裡面加上Timer的方法，其中我設定讓這個block每0.2秒的時候做一次，就會看起來很像頭一直在移動
timer = Timer.scheduledTimer(withTimeInterval: 0.2, repeats: true, block: { (action) in self.bodyRun(height: height, width: width)})

再來進入func裡面，func裡面帶了兩個傳入值，主要是用來計算下個點要往哪裡跑

//身體跟頭方向動
func bodyRun(height:CGFloat,width:CGFloat){
    if self.snakePoint[0].center != self.randomView.center{  //當沒有吃到蘋果的時候就會執行這裡面的func
        runViewArrary()
        headDirection(height: height, width: width)
    }else{                            //當吃到蘋果就會執行下面的程式碼
        var view = UIView.init()      //先把吃到的view加到蛇的陣列裡面
        view = randomView
        let lastPoint = self.snakePoint[self.snakePoint.count - 1].center //把最後的view的座標給吃到的蘋果，這樣就會跟著頭一起跑了
        view.center = lastPoint
        runViewArrary()
        headDirection(height: height, width: width)
        self.snakePoint.append(view)
        self.mainView.score.text = String(snakePoint.count-1)
        self.randomView(height: height, width: width)     //吃到蘋果後就繼續亂數產生下一個點
        for i in 1..<snakePoint.count{
            if randomView.center == snakePoint[i].center{
                randomView(height: height, width: width)
            }
        }
    }
}

裡面有幾個func的作用在下面說明

• 讓身體可以跟著頭跑

//身體動作
func runViewArrary(){
    var tempPoint:[CGPoint] = []
    for i in snakePoint{
        tempPoint.append(i.center)
    }
    for i in 1..<snakePoint.count{
        snakePoint[i].center = tempPoint[i-1]
    }
}

• 再來我們利用方向去算出下個點要往哪裡跑

//頭方向
func headDirection(height:CGFloat,width:CGFloat){
    let point = self.snakePoint[0].center
    if self.nowDirection == .up{   //如果是向上的話就讓頭的y持續減10px()
        if point.y >= 10{
            self.snakePoint[0].center = CGPoint(
                x: self.snakePoint[0].center.x,
                y: self.snakePoint[0].center.y - 10)
        }else{
            self.snakePoint[0].center.y = height - 5
        }
    }else if self.nowDirection == .down{
        if point.y <= height - 10{
            self.snakePoint[0].center = CGPoint(
                x: self.snakePoint[0].center.x,
                y: self.snakePoint[0].center.y + 10)
        }else{
            self.snakePoint[0].center.y = 5
        }
    }else if self.nowDirection == .left{
        if point.x >= 10 {
            self.snakePoint[0].center = CGPoint(
                x: self.snakePoint[0].center.x - 10,
                y: self.snakePoint[0].center.y)
        }else{
            self.snakePoint[0].center.x = width - 5
        }
    }else if self.nowDirection == .right{
        if point.x <= width - 10{
            self.snakePoint[0].center = CGPoint(
                x: self.snakePoint[0].center.x + 10,
                y: self.snakePoint[0].center.y)
        }else{
            self.snakePoint[0].center.x = 5
        }
    }
    var tempPoint:[CGPoint] = []
    for i in snakePoint{
        tempPoint.append(i.center)
    }
    //以下等等再講，這是動畫的部分
    for i in 1..<snakePoint.count{
        if self.snakePoint[0].center == tempPoint[i]{
            ani = UIDynamicAnimator(referenceView: mainView.secondView)
            //引力
            let gravity = UIGravityBehavior(items: snakePoint)
            //碰撞
            let collision = UICollisionBehavior(items: snakePoint)
            //在邊界停止
            collision.translatesReferenceBoundsIntoBoundary = true
            //重力加速度的方向
            gravity.gravityDirection = CGVector (dx: 0.0, dy: 1.0)
            let itemBehavior = UIDynamicItemBehavior(items: snakePoint)
            //碰到牆旋轉速度
            itemBehavior.angularResistance = 0
            //反彈力
            itemBehavior.elasticity = 1.0
            ani.addBehavior(itemBehavior)
            ani.addBehavior(collision)
            ani.addBehavior(gravity)
            timer?.invalidate()
            viewSlideUp()
        }
    }
}

• 產生出下一顆蘋果，並讓蘋果中心的座標隨機產生，並讓它的顏色也是隨機產生的

//蘋果
func randomView(height:CGFloat,width:CGFloat){
    let x = arc4random_uniform(UInt32((width/5)-1))
    let y = arc4random_uniform(UInt32((height/5)-1))
    if (x % 2 != 0) && (y % 2 != 0){
        randomView = UIView.init(frame: CGRect.init(x: 0, y: 0, width: 10, height: 10))
        randomColor()
        randomView.layer.cornerRadius = randomView.frame.width / 2
        randomView.clipsToBounds = true
        randomView.center = CGPoint(x: CGFloat(x) * 5, y: CGFloat(y) * 5)
        self.mainView.secondView.addSubview(randomView)
    }else{
        randomView(height: height, width: width)
    }
}
//蘋果顏色
func randomColor(){
    let red:CGFloat = CGFloat(Float(arc4random_uniform(100))/Float(100))
    let green:CGFloat = CGFloat(Float(arc4random_uniform(100))/Float(100))
    let blue:CGFloat = CGFloat(Float(arc4random_uniform(100))/Float(100))
    let RandomColor = UIColor(red: red, green: green, blue: blue, alpha: 1)
    randomView.backgroundColor = RandomColor
}

今天就先介紹到這邊，明天再來介紹結束遊戲後的處理。