Swift：使用drawStroke绘制半透明线（_：touch :)

Question

我正在尝试使用drawStroke（_：touch :)绘制半透明线。我已经改变了上下文的alpha值，但是没有更轻的刷子得到了虚线。我认为触摸处理有问题。有没有办法避免这种情况？

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

UIGraphicsBeginImageContextWithOptions(bounds.size, false, 0.0)
let context = UIGraphicsGetCurrentContext()

// Draw previous image into context
image?.draw(in: bounds)

drawStroke(context, touch: touch)
// Update image
image = UIGraphicsGetImageFromCurrentImageContext()
  UIGraphicsEndImageContext()
}

fileprivate func drawStroke(_ context: CGContext?, touch: UITouch) {
let previousLocation = touch.previousLocation(in: self)
let location = touch.location(in: self)

// Calculate line width for drawing stroke
let lineWidth = lineWidthForDrawing(context, touch: touch)

// Set color
drawColor.setStroke()

//Change Alpha
context?.setAlpha(0.3)
context?.setBlendMode(.darken)

// Configure line
context?.setLineWidth(lineWidth)
context?.setLineCap(.round)


// Set up the points
context?.move(to: CGPoint(x: previousLocation.x, y: previousLocation.y))
context?.addLine(to: CGPoint(x: location.x, y: location.y))
// Draw the stroke
context?.strokePath()

}

Answer 1

如果您在设置strokeColor时设置了alpha，或者直接设置了像context?.setAlpha(0.3)这样的对象，那么这将使用上面的op图像绘制线条，这是我的解决方法，它完美无缺

只需获取两个imageView并重叠第二个（tempImageView）并在其上绘制图像并在触摸结束时将其传递给main。

// declare
var opacity = 1.0
var isSwiping = false

@IBAction func drawLineWithAlpha(_ sender: UIButton){
    opacity = 0.7
}  

@IBAction func drawSimpleLine(_ sender: UIButton){
    opacity = 1.0
}

override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?){
    isSwiping = true;
    drawLine(capMode: .round, touches: touches, blendMode: .normal)
}

func drawLine(capMode: CGLineCap, touches: Set<UITouch>, blendMode: CGBlendMode){

  let imageViewTouch:UIImageView = self.tempImageView

  if let touch = touches.first{

     let currentPoint = touch.location(in: imageViewTouch)
       UIGraphicsBeginImageContextWithOptions(imageViewTouch.frame.size, false, 0)
     imageViewTouch.image?.draw(in: CGRect(x: 0, y: 0, width: imageViewTouch.frame.size.width, height: imageViewTouch.frame.size.height))          
     UIGraphicsGetCurrentContext()?.move(to: CGPoint(x: lastPoint.x, y: lastPoint.y))
     UIGraphicsGetCurrentContext()?.addLine(to: CGPoint(x: currentPoint.x, y: currentPoint.y))

     UIGraphicsGetCurrentContext()?.setLineCap(capMode)
     UIGraphicsGetCurrentContext()?.setLineWidth(8.0)

     UIGraphicsGetCurrentContext()?.setStrokeColor(red: red, green: green, blue: blue, alpha: 1.0)
     UIGraphicsGetCurrentContext()?.setBlendMode(blendMode)
     UIGraphicsGetCurrentContext()?.strokePath()
     imageViewTouch.image = UIGraphicsGetImageFromCurrentImageContext()
     imageViewTouch.alpha = opacity
     UIGraphicsEndImageContext()
     lastPoint = currentPoint

  }  
}

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

    UIGraphicsBeginImageContext(mainImageView.frame.size)
    mainImageView.image?.draw(in: CGRect(x: 0, y: 0, width: view.frame.size.width, height: view.frame.size.height), blendMode: .normal, alpha: 1.0)

    tempImageView.image?.draw(in: CGRect(x: 0, y: 0, width: view.frame.size.width, height: view.frame.size.height), blendMode: .normal, alpha: opacity)
    mainImageView.image = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()

    tempImageView.image = nil

    print("touchesEnded")
    if(!isSwiping) {
        // code for touch end 
    }
}

发送此ans只是为了更新SO存储库。