使用Swift和SpriteKit写一个忍者游戏

这篇文章的游戏使用SpriteKit和Swift语言来完毕。

SpriteKit是苹果自己的游戏引擎，更能贴合iOS系统底层的API,只是架构和实现上都是模仿了Cocos2D。所以使用上事实上区别不大，只是SpriteKit更轻量级一些。

程序入口

main函数跟OC一样，将入口指向了appdelegate,而cocoa touch框架差点儿跟OC一样，仅仅只是用Swift重写了一遍。

这些模板自带的方法跟OC项目并无差异。。。

開始编写游戏

假设你了解CCNode，CCSprite，CCScene等那看起SpriteKit差点儿没有不论什么问题。

override func viewWillLayoutSubviews() {
        super.viewWillLayoutSubviews()

        var skView : SKView = self.view as SKView
        if !skView.scene {
            //DEBUG
            skView.showsFPS = true
            skView.showsNodeCount = true

            var scene : SKScene = GameScene.sceneWithSize(skView.bounds.size)
            scene.scaleMode = .AspectFill

            skView.presentScene(scene)
        }
    }

因为当viewDidLoad方法被调用时，skView还没有被加到view的层级结构上，因而它不能相应方向以及布局的改变。所以skView的bounds属性此时还不是它横屏后的正确值，而是默认竖屏所相应的值，看来这个时候不是初始化scene的好时机。所以我们须要将这部分代码挪到将要布局子视图的方法中。

播放背景音乐

这里我们使用AVAudioPlayer来播放音乐。

Controller中声明一个属性

var backgroundMusicPlayer : AVAudioPlayer?

func setupMedia() {

        var error : NSError?
        let backgroundMusicURL : NSURL = NSBundle.mainBundle().URLForResource(BG_MUSIC_NAME, withExtension: "caf")
        backgroundMusicPlayer = AVAudioPlayer(contentsOfURL: backgroundMusicURL , error: &error)
        if error {
            println("load background music error : \(error)")
        } else {
            backgroundMusicPlayer!.numberOfLoops = -1
            backgroundMusicPlayer!.prepareToPlay()
            backgroundMusicPlayer!.play()
        }
    }

override func viewDidLoad() {
        super.viewDidLoad()
        setupMedia()
    }

在视图载入完成时開始播放。

游戏场景

我们建了一个SKScene的子类来进行游戏显示和逻辑的编写。

class GameScene: SKScene

胜利失败场景

class GameOverScene : SKScene {

    convenience init(size: CGSize, won: Bool) {
        self.init(size: size)
        self.backgroundColor = SKColor(red:1.0, green:1.0, blue:1.0, alpha:1.0)

        self.setupMsgLabel(isWon :won)
        self.directorAction()
    }

    func setupMsgLabel(isWon won: Bool) {
        var msg: String = won ? "Yow Won!" : "You Lose :["

        var msgLabel = SKLabelNode(fontNamed: "Chalkduster")
        msgLabel.text = msg
        msgLabel.fontSize = 40
        msgLabel.fontColor = SKColor.blackColor()
        msgLabel.position = CGPointMake(self.size.width/2, self.size.height/2)
        self.addChild(msgLabel)
    }

    func directorAction() {
        var actions: AnyObject[] = [ SKAction.waitForDuration(3.0), SKAction.runBlock({
            var reveal = SKTransition.flipHorizontalWithDuration(0.5)
            var gameScene = GameScene(size: self.size)
            self.view.presentScene(gameScene, transition: reveal)
            }) ]
        var sequence = SKAction.sequence(actions)

        self.runAction(sequence)
    }

}

一个简单的显示游戏胜利和失败的页面，仅仅有一个label和一些action。

初始化

var player: SKSpriteNode!  //英雄精灵
    var lastSpawnTimeInterval: NSTimeInterval! //记录上次时间和更新时间
    var lastUpdateTimeInterval: NSTimeInterval!
    var monstersDestroyed: Int! //记录被消灭的怪兽数量

init(size: CGSize) {
        super.init(size: size)

        self.backgroundColor = SKColor(red: 1.0, green:1.0, blue:1.0, alpha:1.0)
        player = SKSpriteNode(imageNamed: "player")
        player.position = CGPointMake(self.player.size.width/2, self.frame.size.height/2)
        self.addChild(player)

        monstersDestroyed = 0
        lastSpawnTimeInterval = 0
        lastUpdateTimeInterval = 0

        gameLevel.nextLevel()

        //physics
        self.physicsWorld.gravity = CGVectorMake(0, 0)
        self.physicsWorld.contactDelegate = self
    }

声明了一些属性并在构造过程中进行了赋值。实例化了英雄精灵。

设置了主要的物理引擎属性。

加入怪兽

func addMonster() {
        var monster = SKSpriteNode(imageNamed: "monster")

        //location
        var minY = monster.size.height/2
        var maxY = self.frame.size.height - monster.size.height/2
        var rangeY = maxY - minY
        var actualY = arc4random() % rangeY + minY

        monster.position = CGPointMake(self.frame.size.width + monster.size.width/2, actualY)
        self.addChild(monster)

        //physics
        monster.physicsBody = SKPhysicsBody(rectangleOfSize: monster.size)
        monster.physicsBody.dynamic = true
        monster.physicsBody.categoryBitMask = monsterCategory
        monster.physicsBody.contactTestBitMask = projectileCategory
        monster.physicsBody.collisionBitMask = 0

        //speed
        var minDuration = 2.0
        var maxDuration = 4.0
        var rangeDuration = maxDuration - minDuration
        var actualDuration = arc4random() % rangeDuration + minDuration

        var actionMove = SKAction.moveTo(CGPointMake(-monster.size.width/2, actualY), duration: actualDuration)
        var actionMoveDone = SKAction.removeFromParent()
        var loseAction = SKAction.runBlock({
            var reveal = SKTransition.flipHorizontalWithDuration(0.5)
            var gameOverScene = GameOverScene(size: self.size, won: false)
            self.view.presentScene(gameOverScene, transition: reveal)
            })

        monster.runAction(SKAction.sequence([actionMove, loseAction, actionMoveDone]))
    }

对怪物进行了初始化，物理配置，速度设置而且让其行动，假设超出了左边界则判定为游戏失败，假设中途碰到忍者发出的飞镖则会销毁，这部分由碰撞检測来实现，稍后会提到。

加入飞镖

当我们点击屏幕结束的时候，须要发射飞镖来进行攻击。

系统有自带监听方法，和UIKit中的一样。

override func touchesEnded(touches: NSSet!, withEvent event: UIEvent!) {
        // get touch
        var touch = touches.anyObject() as UITouch
        var location = touch.locationInNode(self)

        //bullet action
        self.addProjectile(location: location)
    }

然后是加入子弹的方法

func addProjectile(#location: CGPoint) {
        var projectile = SKSpriteNode(imageNamed:"projectile")
        projectile.position = player.position

        //physics
        projectile.physicsBody = SKPhysicsBody(circleOfRadius: projectile.size.width/2)
        projectile.physicsBody.dynamic = true
        projectile.physicsBody.categoryBitMask = projectileCategory
        projectile.physicsBody.contactTestBitMask = monsterCategory
        projectile.physicsBody.collisionBitMask = 0
        projectile.physicsBody.usesPreciseCollisionDetection = true

        var offset = niSub(location, projectile.position)
        if offset.x < 0 {return}

        self.addChild(projectile)

        // direct unit vector
        var direction = niNormalize(offset)
        //to screen's edge
        var shootAmount = niMult(direction, 1000)
        //now loc
        var realDest = niAdd(shootAmount, projectile.position)

        //action
        var velocity = 480.0/1.0
        var realMoveDuration = Double(self.size.width) / velocity

        var actionMove = SKAction.moveTo(realDest, duration: realMoveDuration)
        var actionMoveDone = SKAction.removeFromParent()
        var sequence = SKAction.sequence([actionMove, actionMoveDone])
        projectile.runAction(sequence)

        self.runAction(SKAction.playSoundFileNamed("pew-pew-lei.caf", waitForCompletion: false))
    }

跟怪兽一样，我们对飞镖进行了初始化，物理状态配置，然后去依据点击的位置和英雄的位置去确定它的向量方向，好让他開始移动。之后让他在那个方向上去移动。

游戏辅助

在确定方向移动时我们用到了一些自己定义的闭包函数，而且因为Swift是类型安全语言，非常多时候我们不能直接对不同类型的数值进行运算，所以如同在c++中有的一样，Swift也能够进行运算符重载。

// overload
@infix func %(lhs: UInt32, rhs: Float) -> Float {
    return Float(lhs) % Float(rhs)
}
@infix func %(lhs: UInt32, rhs: Double) -> Double {
    return Double(lhs) % Double(rhs)
}

let niAdd = {(a: CGPoint, b: CGPoint) -> CGPoint in CGPointMake(a.x + b.x, a.y + b.y)}
let niSub = {(a: CGPoint, b: CGPoint) -> CGPoint in CGPointMake(a.x - b.x, a.y - b.y)}
let niMult = {(a: CGPoint, b: Float) -> CGPoint in CGPointMake(a.x * b, a.y * b)}
let niLength = {(a: CGPoint) -> CGFloat in CGFloat(sqrt(Double(a.x * a.x + a.y * a.y)))}

// unit vector
let niNormalize = {(a : CGPoint) -> CGPoint in
    var length = niLength(a)
    return CGPointMake(a.x / length, a.y / length)
}

适合的时机加入怪兽

能够注意到我们之前并没有调用加入怪兽的方法，在iOS系统中，每秒的帧数为60，而在SKScene中，刷新帧会有默认的方法update来进行游戏逻辑的编写。

override func update(currentTime: NSTimeInterval) {
        var timeSinceLast: CFTimeInterval = currentTime - lastSpawnTimeInterval
        lastUpdateTimeInterval = currentTime
        if timeSinceLast > 1 {
            timeSinceLast = Double(gameLevel.toRaw()) / 60.0
            lastUpdateTimeInterval = currentTime
        }

        self.updateWithTimeSinceLastUpdate(timeSinceLast: timeSinceLast)
    }

这时我们便能够加入怪兽了

func updateWithTimeSinceLastUpdate(#timeSinceLast: CFTimeInterval) {
        lastSpawnTimeInterval = lastSpawnTimeInterval + timeSinceLast
        if lastSpawnTimeInterval > 1 {
            lastSpawnTimeInterval = 0
            self.addMonster()
        }
    }

碰撞检測

最后则是须要对碰撞逻辑进行定义。

物理模型有联系时会有代理方法回调。

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

        if (contact.bodyA.categoryBitMask < contact.bodyB.categoryBitMask)
        {
            firstBody = contact.bodyA;
            secondBody = contact.bodyB;
        }
        else
        {
            firstBody = contact.bodyB;
            secondBody = contact.bodyA;
        }

        if (firstBody.categoryBitMask & projectileCategory) != 0 && (secondBody.categoryBitMask & monsterCategory) != 0 {
            self.didCollide(projectile: firstBody.node as SKSpriteNode, monster: secondBody.node as SKSpriteNode)
        }
    }

这时我们希望是怪兽和飞镖碰撞时再进行以下的逻辑

func didCollide(#projectile: SKSpriteNode, monster: SKSpriteNode) {
        projectile.removeFromParent()
        monster.removeFromParent()

        monstersDestroyed = monstersDestroyed + 1
        if monstersDestroyed > 30 {
            var reveal = SKTransition.flipHorizontalWithDuration(0.5)
            var gameOverScene = GameOverScene(size: self.size, won: true)
            self.view.presentScene(gameOverScene, transition: reveal)
        }
    }

这样整个忍者飞镖怪兽的游戏就完毕了。

以下是游戏截图：