ios - 如何防止CGContext中风路径或绘制路径线条画向上 float /旋转回来？

Question

使用 Swift 画线，我继续画的时间越长，它就会不断向上移动。或者它可能会向后旋转，就像在球上一样？这些图片显示我从一条线开始，然后当我绘制时，你可以看到它到达了正方形的顶部。太奇怪了!为什么会发生这种情况？我怎样才能阻止它？代码如下。

var context: CGContext?
var adjustedImageViewRect: CGRect?
var adjustedImageView: UIImageView?

var lastPoint = CGPoint.zero
var firstPoint = CGPoint.zero
var brushWidth: CGFloat = 10.0
var opacity: CGFloat = 1.0
var swiped = false

var undermineArray: [CGPoint] = []

@IBOutlet weak var drawLineImageView: UIImageView!

override func viewDidLoad() {
    super.viewDidLoad()
    drawLineImageView.image = UIImage(named: "layer")
}

override func viewDidAppear(_ animated: Bool) {
    let rect = AVMakeRect(aspectRatio: drawLineImageView.image!.size, insideRect: drawLineImageView.bounds)
    adjustedImageViewRect = rect

    adjustedImageView = UIImageView(frame: rect)
    self.view.addSubview(adjustedImageView!)
    self.view.bringSubview(toFront: adjustedImageView!)
}

func drawLine(from fromPoint: CGPoint, to toPoint: CGPoint) {

    if let adjImgView = adjustedImageView {
        if let adjImgViewRect = adjustedImageViewRect {

            UIGraphicsBeginImageContextWithOptions(adjImgViewRect.size, false, 0)

            adjImgView.image?.draw(in: adjImgView.bounds)

            context = UIGraphicsGetCurrentContext()
            context?.move(to: fromPoint)
            context?.addLine(to: toPoint)
            context?.setLineCap(CGLineCap.round)
            context?.setLineWidth(brushWidth)
            context?.setStrokeColor(UIColor.red.cgColor)
            context?.setBlendMode(CGBlendMode.normal)
            context?.strokePath()

            adjImgView.image = UIGraphicsGetImageFromCurrentImageContext()
            UIGraphicsEndImageContext()
        }
    }
}

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    //clear out previous line
    firstPoint = CGPoint.zero
    lastPoint = CGPoint.zero
    undermineArray.removeAll()

    adjustedImageView?.image = UIImage()
    swiped = false
    if let touch = touches.first {
        if let rect = adjustedImageViewRect {
            if (touch.location(in: self.adjustedImageView).y < 0
                || touch.location(in: self.adjustedImageView).y > rect.height) {
                adjustedImageView?.image = UIImage()
                return
            }
        }
        firstPoint = touch.location(in: self.adjustedImageView)
        lastPoint = touch.location(in: self.adjustedImageView)
        undermineArray.append(firstPoint)
    }
}

override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
    swiped = true
    if let touch = touches.first {

        var currentPoint = touch.location(in: adjustedImageView)
        if let rect = adjustedImageViewRect {
            if (touch.location(in: self.adjustedImageView).y < 0) {
                currentPoint.y = 0
            }

            if (touch.location(in: self.adjustedImageView).y > rect.height) {
                currentPoint.y = rect.height
            }
        }

        undermineArray.append(currentPoint)
        drawLine(from: lastPoint, to: currentPoint)
        lastPoint = currentPoint
    }
}

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

    if let rect = adjustedImageViewRect {
        if (firstPoint.y < 0 || firstPoint.y > rect.height) {
            adjustedImageView?.image = UIImage()
            return
        }
    }

    if let touch = touches.first {
        if let rect = adjustedImageViewRect {
            if (touch.location(in: self.adjustedImageView).y < 0) {
                lastPoint.y = 0
            }
            if (touch.location(in: self.adjustedImageView).y > rect.height) {
                lastPoint.y = rect.height
            }
        }
    }

    if !swiped {
        self.drawLine(from: lastPoint, to: lastPoint)
    }
}

Answer 1

啊我明白了。事实证明，UIImage 的 draw() 函数绘制了图像，直到现在我才知道，“根据需要缩放它以适合。”

所以，我们将使用其他东西。我们将只使用drawAsPattern()。

改变

adjImgView.image?.draw(in: adjImgView.bounds)

至

adjImgView.image?.drawAsPattern(in: adjImgView.bounds)

瞧，没有发生疯狂的缩放/旋转/缩小。