在Swift中消除UIBezierPath平滑线中的滞后延迟

Question

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。

1. 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？

2. 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.
   }
   

   }

Answer 1

1. 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。

1. 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。