ios – 逐步提高SpriteKit中滚动背景的速度

2019年8月6日 181次阅读

我在SpriteKit中制作一个简单的游戏,我有一个滚动的背景.简单发生的是,当加载游戏场景时,一些背景图像彼此相邻放置,然后当图像滚出屏幕时图像被水平移动.这是我的游戏场景的didMoveToView方法的代码.

// self.gameSpeed is 1.0 and gradually increases during the game

let backgroundTexture = SKTexture(imageNamed: "Background")
var moveBackground = SKAction.moveByX(-self.frame.size.width, y: 0, duration: (20 / self.gameSpeed))
var replaceBackground = SKAction.moveByX(self.frame.size.width, y: 0, duration: 0)
var moveBackgroundForever = SKAction.repeatActionForever(SKAction.sequence([moveBackground, replaceBackground]))

for var i:CGFloat = 0; i < 2; i++ {
    var background = SKSpriteNode(texture: backgroundTexture)
    background.position = CGPoint(x: self.frame.size.width / 2 + self.frame.size.width * i, y: CGRectGetMidY(self.frame))
    background.size = self.frame.size
    background.zPosition = -100
    background.runAction(moveBackgroundForever)

    self.addChild(background)
}

现在我想在游戏的某些点增加滚动背景的速度.您可以看到背景水平滚动的持续时间设置为(20 / self.gameSpeed).显然这不起作用,因为此代码只运行一次,因此移动速度永远不会更新以考虑self.gameSpeed变量的新值.

所以,我的问题很简单：如何根据self.gameSpeed变量提高背景图像移动的速度(缩短持续时间)？

谢谢！

最佳答案 您可以使用gameSpeed变量来设置背景的速度.为了实现这一点,首先,您需要引用您的两个背景片段(如果您愿意,还需要更多)：

class GameScene: SKScene {
    lazy var backgroundPieces: [SKSpriteNode] = [SKSpriteNode(imageNamed: "Background"), 
                                                 SKSpriteNode(imageNamed: "Background")]

    // ... 
}

现在你需要你的gameSpeed变量：

var gameSpeed: CGFloat = 0.0 {
    // Using a property observer means you can easily update the speed of the 
    // background just by setting gameSpeed.
    didSet {
        for background in backgroundPieces {
            // Minus, because the background is moving from left to right.
            background.physicsBody!.velocity.dx = -gameSpeed
        }
    }
}

然后在didMoveToView中正确定位每个部分.此外,对于这种方法来处理每个背景片需要一个物理体,以便您可以轻松地改变其速度.

override func didMoveToView(view: SKView) {
    for (index, background) in enumerate(backgroundPieces) {
        // Setup the position, zPosition, size, etc...

        background.physicsBody = SKPhysicsBody(rectangleOfSize: background.size)
        background.physicsBody!.affectedByGravity = false
        background.physicsBody!.linearDamping = 0
        background.physicsBody!.friction = 0

        self.addChild(background)
    }

    // If you wanted to give the background and initial speed,
    // here's the place to do it.
    gameSpeed = 1.0
}

您可以在update中更新gameSpeed,例如gameSpeed = 0.5.

最后,在更新中,您需要检查背景片是否已经离屏(左侧).如果有,则需要将其移动到背景片段的末尾：

override func update(currentTime: CFTimeInterval) {
    for background in backgroundPieces {
        if background.frame.maxX <= 0 {
            let maxX = maxElement(backgroundPieces.map { $0.frame.maxX })

            // I'm assuming the anchor of the background is (0.5, 0.5)
            background.position.x = maxX + background.size.width / 2
        }
    }
}
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