在Swift中消除UIBezierPath平滑线中的滞后延迟

小编典典

在Swift中消除UIBezierPath平滑线中的滞后延迟

swift

下面的代码通过覆盖触摸来绘制平滑的曲线，但是存在明显的滞后或延迟。该代码每隔4个接触点使用addCurveToPoint并调用setNeedsDisplay一次，这会导致跳动的外观，因为图形无法跟上手指的移动。为了消除延迟或察觉到的延迟，可以用addQuadCurveToPoint和临时填充触摸点1、2、3（直至触摸点4）addLineToPoint。

在代码中，如何在显示最终弯曲线之前通过使用临时线和QuadCurved线来实际消除滞后现象，从而在代码中实现呢？

如果将下面的类附加到一个类UIView（例如viewOne或self）上，如何UIView在该类之后将图形副本复制到该类之外的另一个类（例如viewTwo）上touchesEnded？

 //  ViewController.swift

import UIKit

class drawSmoothCurvedLinesWithLagging: UIView {

let path=UIBezierPath()
var incrementalImage:UIImage?

var points = [CGPoint?](count: 5, repeatedValue: nil)

var counter:Int?

var strokeColor:UIColor?

required init?(coder aDecoder: NSCoder) {
    super.init(coder: aDecoder)
}

override func drawRect(rect: CGRect) {
    autoreleasepool {
        incrementalImage?.drawInRect(rect)
        strokeColor = UIColor.blueColor()
        strokeColor?.setStroke()
        path.lineWidth = 20
        path.lineCapStyle = CGLineCap.Round
        path.stroke()
    }
}

override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
    counter = 0

    let touch: AnyObject? = touches.first
    points[0] = touch!.locationInView(self)
}

override func touchesMoved(touches: Set<UITouch>, withEvent event: UIEvent?) {
    let touch: AnyObject? = touches.first
    let point = touch!.locationInView(self)

    counter = counter! + 1
    points[counter!] = point

    if counter == 2{
        //use path.addLineToPoint ?
        //use self.setNeedsDisplay() ?
    }

    if counter == 3{
        //use path.addQuadCurveToPoint ?
        //use self.setNeedsDisplay() ?
    }

    if counter == 4{
        points[3]! = CGPointMake((points[2]!.x + points[4]!.x)/2.0, (points[2]!.y + points[4]!.y)/2.0)
        path.moveToPoint(points[0]!)
        path.addCurveToPoint(points[3]!, controlPoint1: points[1]!, controlPoint2: points[2]!)

        self.setNeedsDisplay()

        points[0]! = points[3]!
        points[1]! = points[4]!
        counter = 1
    }
}

override func touchesEnded(touches: Set<UITouch>, withEvent event: UIEvent?) {
    self.drawBitmap()
    self.setNeedsDisplay()
    path.removeAllPoints()
    counter = 0
}

override func touchesCancelled(touches: Set<UITouch>?, withEvent event: UIEvent?) {
    self.touchesEnded(touches!, withEvent: event)
}

func drawBitmap(){
    UIGraphicsBeginImageContextWithOptions(self.bounds.size, true, 0.0)
    strokeColor?.setStroke()
    if((incrementalImage) == nil){
        let rectPath:UIBezierPath = UIBezierPath(rect: self.bounds)
        UIColor.whiteColor().setFill()
        rectPath.fill()
    }

    incrementalImage?.drawAtPoint(CGPointZero)
    path.stroke()
    incrementalImage = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
}

}

class ViewController: UIViewController {

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

}

阅读 409

2020-07-07

共1个答案

小编典典

是的，每隔几个点添加一条曲线会产生滞后的滞后。因此，是的，您可以通过向添加一条线points[1]，向添加一条四边形曲线points[2]和向添加一条三次曲线来减少这种影响points[3]。

正如您所说，请确保将其添加到单独的路径。因此，在Swift 3/4中：

    class SmoothCurvedLinesView: UIView {
    var strokeColor = UIColor.blue
    var lineWidth: CGFloat = 20
    var snapshotImage: UIImage?

    private var path: UIBezierPath?
    private var temporaryPath: UIBezierPath?
    private var points = [CGPoint]()

    override func draw(_ rect: CGRect) {
        snapshotImage?.draw(in: rect)

        strokeColor.setStroke()

        path?.stroke()
        temporaryPath?.stroke()
    }

    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        if let touch = touches.first {
            points = [touch.location(in: self)]
        }
    }

    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
        guard let touch = touches.first else { return }
        let point = touch.location(in: self)

        points.append(point)

        updatePaths()

        setNeedsDisplay()
    }

    private func updatePaths() {
        // update main path

        while points.count > 4 {
            points[3] = CGPoint(x: (points[2].x + points[4].x)/2.0, y: (points[2].y + points[4].y)/2.0)

            if path == nil {
                path = createPathStarting(at: points[0])
            }

            path?.addCurve(to: points[3], controlPoint1: points[1], controlPoint2: points[2])

            points.removeFirst(3)

            temporaryPath = nil
        }

        // build temporary path up to last touch point

        if points.count == 2 {
            temporaryPath = createPathStarting(at: points[0])
            temporaryPath?.addLine(to: points[1])
        } else if points.count == 3 {
            temporaryPath = createPathStarting(at: points[0])
            temporaryPath?.addQuadCurve(to: points[2], controlPoint: points[1])
        } else if points.count == 4 {
            temporaryPath = createPathStarting(at: points[0])
            temporaryPath?.addCurve(to: points[3], controlPoint1: points[1], controlPoint2: points[2])
        }
    }

    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
        finishPath()
    }

    override func touchesCancelled(_ touches: Set<UITouch>?, with event: UIEvent?) {
        finishPath()
    }

    private func finishPath() {
        constructIncrementalImage()
        path = nil
        setNeedsDisplay()
    }

    private func createPathStarting(at point: CGPoint) -> UIBezierPath {
        let localPath = UIBezierPath()

        localPath.move(to: point)

        localPath.lineWidth = lineWidth
        localPath.lineCapStyle = .round
        localPath.lineJoinStyle = .round

        return localPath
    }

    private func constructIncrementalImage() {
        UIGraphicsBeginImageContextWithOptions(bounds.size, false, 0.0)
        strokeColor.setStroke()
        snapshotImage?.draw(at: .zero)
        path?.stroke()
        temporaryPath?.stroke()
        snapshotImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
    }
}

您甚至可以将此与iOS9预测性触控结合使用如我在其他答案中所述，这可以进一步减少延迟。

要获取生成的图像并将其用于其他地方，您只需抓住incrementalImage（我在snapshotImage上面将其重命名为），然后将其放入另一个视图的图像视图中即可。

2020-07-07