[原创]Swift+Sprite Kit中文教程第三篇

拖了好久的第三篇终于开始了……
ps：由于Xcode7不支持iOS8.4，我最终换回了Yosemite和Xcode6.4，所以语法如果有所出入引起问题，可以谷歌解决或者在下面留言。

添加敌人

为了简便起见，我们将用相同的飞机作为敌人，但是方向和主角飞机相反，从上往下飞（这里解释一下，因为之前使用yScale翻转，结果导致碰撞检测时出现了很诡异的bug，暂时无解，所以我用系统内置的预览工具，将spaceship这张图片进行了上下翻转，然后另存为一个资源，具体如下图。如果有人使用scale并解决问题，可以告知一声，不胜感激）。

var enemyTime:NSTimeInterval = 1
var lastEnemy:NSTimeInterval = 0

在此之前呢，我们先把update函数清理一下。将创建子弹的代码放置到单独的函数中，同时添加创建敌人的函数：

func createBullet(){
    let bullet = SKShapeNode(rectOfSize: CGSizeMake(10, 10))
    bullet.position = CGPointMake(plane.position.x, plane.position.y + 50)
    bullet.strokeColor = UIColor.clearColor()
    bullet.fillColor = UIColor.greenColor()
    addChild(bullet)
    
    bullet.runAction(SKAction.sequence([SKAction.moveByX(0, y: size.height, duration: 2), SKAction.removeFromParent()]))
}

func createEnemy(){
    let enemy = SKSpriteNode(texture: enemyTexture)
    enemy.setScale(0.5)
    enemy.position = CGPointMake(plane.position.x, size.height)
    addChild(enemy)
    
    enemy.runAction(SKAction.sequence([SKAction.moveByX(0, y: -size.height, duration: 4), SKAction.removeFromParent()]))
}

update(){
    //添加到update函数中
    if currentTime >= lastBullet + bulletTime{
        createBullet()
        lastBullet = currentTime
    }
    
    if currentTime >= lastEnemy + enemyTime{
        createEnemy()
        lastEnemy = currentTime
        
    }
}

简洁了很多吧~!
其实和创建子弹是一样的，只不过设定初始Y坐标为屏幕高度，位移方向从上往下，也就是负的屏幕高度值。运行一下，会发现有大量飞机出现在和你相同的竖直方向上。

优化敌人

首先，敌人出现的时间间隔随机一些：

if currentTime >= lastEnemy + enemyTime{
    createEnemy()
    lastEnemy = currentTime
    enemyTime = NSTimeInterval(arc4random() % 20 + 5) / 10
    //一个神奇的经过反复测试得出的还不错的随机时间间隔
}

下一步就是将初始位置随机一些，在createEnemy函数中进行修改：

func createEnemy(){
    let enemy = SKSpriteNode(texture: enemyTexture)
    enemy.setScale(0.5)
    
    var randomX = CGFloat(arc4random()) % size.width
    
    enemy.position = CGPointMake(randomX, size.height)
    addChild(enemy)
    
    enemy.runAction(SKAction.sequence([SKAction.moveByX(0, y: -size.height, duration: 4), SKAction.removeFromParent()]))
}

用随机数对宽度取模，即可轻松搞定~
现在敌人已经成了比较完美的靶标了，准备射击！

添加物理

首先添加三个不明觉厉的后面会用到的东西

let PlayerCategory:UInt32 = 1<<1
let BulletCategory:UInt32 = 1<<2
let EnemyCategory:UInt32 = 1<<3

这个其实是碰撞标记，这篇博客里简单提到了，其实就是把需要互相碰撞的物体进行一个归类，设定和检测彼此的碰撞，并且发送碰撞消息。目前用到的标记有三个：我方飞机、子弹、敌方飞机。

先给子弹添加物理效果：

bullet.physicsBody = SKPhysicsBody(rectangleOfSize: CGSizeMake(10, 10))
bullet.physicsBody?.categoryBitMask = BulletCategory
bullet.physicsBody?.collisionBitMask = 0
bullet.physicsBody?.contactTestBitMask = EnemyCategory

分别是创建物理盒，所属标记，碰撞标记，碰撞通知标记。碰撞消息的产生不受碰撞标记设置的影响，碰撞标记只关系到是否模拟碰撞效果。物理盒大小我们可以自己设定，如果使用了纹理，也可以用纹理的size属性进行设置，就比如接下来的敌人物理盒创建。
planeTexture下面添加let enemyTexture = SKTexture(imageNamed: "Enemy")
createEnemy函数中添加：

enemy.physicsBody = SKPhysicsBody(rectangleOfSize: enemyTexture.size())
enemy.physicsBody?.categoryBitMask = EnemyCategory
enemy.physicsBody?.collisionBitMask = 0
enemy.physicsBody?.contactTestBitMask = BulletCategory

这五行添加到addChild之前即可。
接下来就是最重要的环节了，修改GameScene类定义的这一行，改为：
class GameScene: SKScene, SKPhysicsContactDelegate
继承碰撞检测代理，然后在didMoveToView中添加：

physicsWorld.contactDelegate = self
physicsWorld.gravity = CGVectorMake(0, 0)

表示碰撞检测代理为当前世界盒，并且重力为0，保证任何物体不会向下掉落。
然后在类中任意地方添加一个函数：

func didBeginContact(contact: SKPhysicsContact) {
    if contact.bodyA.categoryBitMask | contact.bodyB.categoryBitMask == BulletCategory | EnemyCategory{
        print("enemy die")
        
        contact.bodyA.node?.removeFromParent()
        contact.bodyB.node?.removeFromParent()
    }
}

用来在碰撞发生时进行操作，首先进行判断，碰撞涉及的两个标记，是否是子弹和敌人标记。如果是，就杀死一个敌人，移除相关的子弹和击中的敌人。跑起来看看吧，已经比较完整了~

全部代码如下：

import SpriteKit

let PlayerCategory:UInt32 = 1<<1
let BulletCategory:UInt32 = 1<<2
let EnemyCategory:UInt32 = 1<<3

class GameScene: SKScene, SKPhysicsContactDelegate {
    
    let planeTexture = SKTexture(imageNamed: "Spaceship")
    let enemyTexture = SKTexture(imageNamed: "Enemy")
    var plane:SKSpriteNode!
    
    var bulletTime:NSTimeInterval = 0.2//子弹发射间隔
    var lastBullet:NSTimeInterval = 0//上次发射的时间点
    var toucheGap = CGPoint(x: 0, y: 0)
    
    var enemyTime:NSTimeInterval = 1
    var lastEnemy:NSTimeInterval = 0
    
    override func didMoveToView(view: SKView) {
        /* Setup your scene here */
        
        physicsWorld.contactDelegate = self
        physicsWorld.gravity = CGVectorMake(0, 0)
        
        plane = SKSpriteNode(texture: planeTexture)
        plane.position = CGPointMake(size.width * 0.5, size.height * 0.5)
        plane.setScale(0.5)
        plane.name = "plane"
        addChild(plane)
    }
    
    override func touchesBegan(touches: Set<NSObject>, withEvent event: UIEvent) {
        /* Called when a touch begins */
        let location:CGPoint! = (touches.first as! UITouch).locationInNode(self)
        toucheGap = CGPoint(x: location.x - plane.position.x, y: location.y - plane.position.y)
    }
    
    override func touchesMoved(touches: Set<NSObject>, withEvent event: UIEvent) {
        let location:CGPoint! = (touches.first as! UITouch).locationInNode(self)
        let xDir = clamp(location.x - toucheGap.x, min: 0, max: size.width)
        let yDir = clamp(location.y - toucheGap.y, min: 0, max: size.height)
        plane.position = CGPoint(x: xDir, y: yDir)
    }
    
    override func touchesEnded(touches: Set<NSObject>, withEvent event: UIEvent) {

    }
    
    func didBeginContact(contact: SKPhysicsContact) {
        if contact.bodyA.categoryBitMask | contact.bodyB.categoryBitMask == BulletCategory | EnemyCategory{
            print("enemy die")
            
            contact.bodyA.node?.removeFromParent()
            contact.bodyB.node?.removeFromParent()
        }
    }
   
    override func update(currentTime: CFTimeInterval) {
        /* Called before each frame is rendered */
        
        if currentTime >= lastBullet + bulletTime{
            createBullet()
            lastBullet = currentTime
        }
        
        if currentTime >= lastEnemy + enemyTime{
            createEnemy()
            lastEnemy = currentTime
            enemyTime = NSTimeInterval(arc4random() % 20 + 5) / 10
        }
        
    }
    
    func createBullet(){
        let bullet = SKShapeNode(rectOfSize: CGSizeMake(10, 10))
        bullet.position = CGPointMake(plane.position.x, plane.position.y + 50)
        bullet.strokeColor = UIColor.clearColor()
        bullet.fillColor = UIColor.greenColor()
        bullet.physicsBody = SKPhysicsBody(rectangleOfSize: CGSizeMake(10, 10))
        bullet.physicsBody?.categoryBitMask = BulletCategory
        bullet.physicsBody?.collisionBitMask = 0
        bullet.physicsBody?.contactTestBitMask = EnemyCategory
        addChild(bullet)
        
        bullet.runAction(SKAction.sequence([SKAction.moveByX(0, y: size.height, duration: 2), SKAction.removeFromParent()]))
    }
    
    func createEnemy(){
        let enemy = SKSpriteNode(texture: enemyTexture)
        enemy.setScale(0.5)
        
        var randomX = CGFloat(arc4random()) % size.width
        
        enemy.position = CGPointMake(randomX, size.height)
        enemy.physicsBody = SKPhysicsBody(rectangleOfSize: enemy.size)
        enemy.physicsBody?.categoryBitMask = EnemyCategory
        enemy.physicsBody?.collisionBitMask = 0
        enemy.physicsBody?.contactTestBitMask = BulletCategory
        addChild(enemy)
        
        enemy.runAction(SKAction.sequence([SKAction.moveByX(0, y: -size.height, duration: 4), SKAction.removeFromParent()]))
    }
    
    func clamp(x: CGFloat, min: CGFloat, max: CGFloat) -> CGFloat{
        if x <= min{
            return min
        }else if x >= max{
            return max
        }else{
            return x
        }
    }
}

下一篇