擦除UIBezierPath

Question

我是徒手画一个UIBezierPath，但现在我想能够擦除我以前画的线。有人对如何做到这一点有什么建议吗？

@objc private func didPanWhiteboard(_ gesture: UIPanGestureRecognizer) {
    let location = gesture.location(in: drawCanvasView)
    
    switch gesture.state {
        case .began:
            path = UIBezierPath()
            path.move(to: location)
            strokeLayer = CAShapeLayer()
            drawCanvasView.layer.addSublayer(strokeLayer)
            path.stroke(with: shouldErase ? .clear : .normal, alpha: 1.0)
            strokeLayer.strokeColor = toolColor.cgColor
            strokeLayer.fillColor = UIColor.clear.cgColor
            strokeLayer.lineWidth = toolWidth
            strokeLayer.path = path?.cgPath
        case .changed:
            path.addLine(to: location)
            strokeLayer.path = path.cgPath
        case .cancelled, .ended: drawLayers.append(strokeLayer)
        default: break
    }
}

我就是这样画线的，到目前为止，为了擦除，我试着：

path.stroke(with: shouldErase ? .clear : .normal, alpha: 1.0)

但当shouldErase是真的时，它似乎什么也不做。

编辑:这就是我想要达到的目标：

https://imgur.com/a/XVfQita

请随意建议任何一种方法。

Answer 1

我设法用CGContext解决了这个问题。

@objc private func didPanWhiteboard(_ gesture: UIPanGestureRecognizer) {
    switch gesture.state {
        case .began:
            drawingState = .began
            lastPoint = gesture.location(in: drawingBoardImageView)
        case .changed:
            drawingState = .moved
            let currentPoint = gesture.location(in: drawingBoardImageView)
            drawLineFrom(fromPoint: lastPoint, toPoint: currentPoint)
            lastPoint = currentPoint
        case .cancelled, .ended:
            drawingState = .ended
            drawLineFrom(fromPoint: lastPoint, toPoint: lastPoint)
        default: break
    }
}


private func drawLineFrom(fromPoint: CGPoint, toPoint: CGPoint) {
    UIGraphicsBeginImageContext(drawingBoardImageView.frame.size)
    let context = UIGraphicsGetCurrentContext()
    tempImageView.image?.draw(in: CGRect(x: 0, y: 0, width: drawingBoardImageView.frame.size.width, height: drawingBoardImageView.frame.size.height))
    context?.move(to: fromPoint)
    context?.addLine(to: toPoint)
    context?.setLineCap(brush.lineCap)
    context?.setAlpha(brush.opacity)
    context?.setLineWidth(brush.width)
    context?.setStrokeColor(brush.color.cgColor)
    if shouldErase {
        context?.setBlendMode(.clear)
    } else {
        context?.setBlendMode(.normal)
    }
    context?.strokePath()
    guard let image = UIGraphicsGetImageFromCurrentImageContext() else { return }
    if drawingState == .ended {
        drawingUndoManager.registerForUndo(image)
    }
    tempImageView.image = image
    tempImageView.alpha = 1.0
    UIGraphicsEndImageContext()
}