创建没有丢帧的无尽 cgpath

Question

我需要不断地创建一个 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

}

然后这样称呼它：

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

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

我的目标是创建一条随机的无限路径。

Answer 1

在绘制线数逐渐增加的同时保持高 FPS 计数的关键是快速达到在场景中添加更多线对帧速率影响很小或没有影响的状态。至少有两种方法可以做到这一点。

两者中最直接的方法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。步骤如下：

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

这是一个在 Swift 中的示例实现，它在 iPhone 6 设备上以 60 FPS 的速度绘制无穷无尽的线条（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()
    }
}