我需要连续创建一个 cgpath。目前我是这样做的:

 func createLine(){
        var rand = randomBetweenNumbers(1, 2)
        currentY--
        if rand < 1.5{
            currentX--
            CGPathAddLineToPoint(leftPath, nil, currentX, currentY)
        }else{
            currentX++
            CGPathAddLineToPoint(leftPath, nil, currentX, currentY)
        }
        CGPathAddLineToPoint(rightPath, nil, currentX+tileSize, currentY)
        lineNode.path = leftPath
        rightNode.path = rightPath

}

然后这样调用它:

NSTimer.scheduledTimerWithTimeInterval(0.05, target: self, selector: Selector("startTile"), userInfo: nil, repeats: true)

但问题是，随着时间的推移，帧数越来越低。有什么我必须改变的，以便帧率不再下降吗？

我的目标是创造一条随机的无尽路径。

最佳答案

在绘制逐渐增加的线条数量的同时保持高 FPS 计数的关键是快速达到一种状态，即向场景添加更多线条对帧速率影响很小或没有影响。至少有两种方法可以做到这一点。

两者中最直接的是定期将先前绘制的线条转换为 SKTexture 并将结果显示为 SKSpriteNode 的纹理。以下是步骤:

1. 创建一个 SKNode 用作行容器
2. 创建一个 SKSpriteNode 用作线条 Canvas
3. 创建一个 SKShapeNode 用于绘制新线
4. 将容器添加到场景中，将 Canvas 和形状节点添加到容器中
5. 使用形状节点的path属性绘制一组相连的线段
6. 当行数达到预定值时，将容器的内容转换为“SKTexture”
7. 将 Canvas 的纹理属性设置为SKTexture。请注意，由于 Canvas 也是容器的子项，因此其内容也将添加到纹理
8. 起泡、冲洗，重复步骤 5 - 7

下面是 Swift 中的一个示例实现，它在 iPhone 6 设备上以 60 FPS 的速度绘制了一组无穷无尽的线条(您应该在不使用模拟器的设备上测试性能):

class GameScene: SKScene {
    // 1. Create container to hold new and old lines
    var lineContainer = SKNode()
    // 2. Create canvas
    var lineCanvas:SKSpriteNode?
    // 3. Create shape to draw new lines
    var lineNode = SKShapeNode()

    var lastDrawTime:Int64 = 0
    var lineCount = 0
    var timeScan:Int64 = 0
    var path = CGPathCreateMutable()

    var lastPoint = CGPointZero

    override func didMoveToView(view:SKView) {
        scaleMode = .ResizeFill

        // 4. Add the container to the scene and the canvas to the container 
        addChild(lineContainer)
        lineCanvas = SKSpriteNode(color:SKColor.clearColor(),size:view.frame.size)
        lineCanvas!.anchorPoint = CGPointZero
        lineCanvas!.position = CGPointZero
        lineContainer.addChild(lineCanvas!)
        lastPoint = CGPointMake(view.frame.size.width/2.0, view.frame.size.height/2.0)
    }

    // Returns a random value in the specified range
    func randomInRange(minValue:CGFloat, maxValue:CGFloat) -> CGFloat {
        let r = CGFloat(Double(arc4random_uniform(UInt32.max))/Double(UInt32.max))
        return (maxValue-minValue) * r + minValue
    }

    func drawLine() {
        if (CGPathIsEmpty(path)) {
            // Create a new line that starts where the previous line ended
            CGPathMoveToPoint(path, nil, lastPoint.x, lastPoint.y)
            lineNode.path = nil
            lineNode.lineWidth = 1.0
            lineNode.strokeColor = SKColor.blueColor()
            lineNode.zPosition = 100
            lineContainer.addChild(lineNode)
        }
        // Add a random line segment
        let x = randomInRange(size.width*0.1, maxValue: size.width*0.9)
        let y = randomInRange(size.height*0.1, maxValue: size.height*0.9)
        CGPathAddLineToPoint(path, nil, x, y)
        lineNode.path = path
        // Save the current point so we can connect the next line to the end of the last line
        lastPoint = CGPointMake(x, y)
    }

    override func update(currentTime: CFTimeInterval) {
        let lineDrawTime = timeScan / 10
        // 5. Draw a new line every 10 updates. Increment line count
        if (lineDrawTime != lastDrawTime) {
            drawLine()
            ++lineCount
        }
        // 6. and 7. Add all newly and previously drawn lines to the canvas
        if (lineCount == 8) {
            addLinesToTexture()
            lineCount = 0
        }
        lastDrawTime = lineDrawTime
        ++timeScan
    }

    func addLinesToTexture () {
        // Convert the contents of the line container to an SKTexture
        let texture = self.view!.textureFromNode(lineContainer)
        // Display the texture
        lineCanvas!.texture = texture
        // Start a new line
        lineNode.removeFromParent()
        path = CGPathCreateMutable()
    }
}

关于swift - 创建没有 framedrops 的无尽 cgpath，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/30514706/