试图用swift擦除uiimage

Posted 2021-04-14

我正在尝试为我的应用程序制作橡皮擦功能（并在将来恢复）但面临一些问题。我正在使用Swift 4.2，这是我到目前为止所做的：

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        if let touch = touches.first as UITouch?{
            let touchPoint = touch.location(in: self.lassoImageView) + lassoOffset!
            print("touch begin to : (touchPoint)")
            eraserStartPoint = touchPoint   
        }
    }

override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
        if let touch = touches.first as UITouch?{
            let touchPoint = touch.location(in: self.lassoImageView) + lassoOffset!
            print("touch moved to : (touchPoint)")
            erase(fromPoint: eraserStartPoint!, toPoint: touchPoint)
            eraserStartPoint = touchPoint
        }
    }

override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
        if let touch = touches.first as UITouch?{
            let touchPoint = touch.location(in: self.lassoImageView) + lassoOffset!
            print("touch ended at : (touchPoint)")
            erase(fromPoint: touchPoint, toPoint: touchPoint)
            UIGraphicsBeginImageContext(lassoImageView.frame.size)
                lassoImageView.image?.draw(in: CGRect(x: 0, y: 0, width: lassoImageView.frame.size.width, height: lassoImageView.frame.size.height), blendMode: .normal, alpha: 1.0)
                lassoImageView.image?.draw(in:  CGRect(x: 0, y: 0, width: lassoImageView.frame.size.width, height: lassoImageView.frame.size.height), blendMode: .normal, alpha: 1.0)
                lassoImageView.image = UIGraphicsGetImageFromCurrentImageContext()
                UIGraphicsEndImageContext()   
    }

func erase(fromPoint: CGPoint, toPoint: CGPoint) {
        UIGraphicsBeginImageContextWithOptions(lassoImageView.bounds.size, false, 1)
        //UIGraphicsBeginImageContext(lassoImageView.bounds.size)
        //UIGraphicsBeginImageContext(lassoImageView.image!.size)
        let context = UIGraphicsGetCurrentContext()
        lassoImageView.image?.draw(in: CGRect(x: 0, y: 0, width: lassoImageView.frame.size.width, height: lassoImageView.frame.size.height))
        //lassoImageView.image?.draw(in: calculateRectOfImageInImageView(imageView: lassoImageView))

        context?.move(to: fromPoint)
        context?.addLine(to: toPoint)

        context?.setLineCap(.round)
        context?.setLineWidth(CGFloat(eraserBrushWidth))

        context?.setBlendMode(.clear)

        context?.strokePath()

        lassoImageView.image = UIGraphicsGetImageFromCurrentImageContext()
        croppedImage = UIGraphicsGetImageFromCurrentImageContext()

        UIGraphicsEndImageContext()
    }

lassoImageView // this is UIImageView where I'm loading image from gallery and then erasing image with my finger

lassoOffset // this is Float for touch offset because finger hides part of image

代码很简单，它实际上有效，但如果图像宽高比不同于UIImageView宽高比。 UIImageView内容模式设置为Aspect Fit，但无论如何，当我拖动我的手指图像变得拉伸，就像它是Scale to Fill

我相信问题在于我的直线：

lassoImageView.image?.draw(in: CGRect(x: 0, y: 0, width: lassoImageView.frame.size.width, height: lassoImageView.frame.size.height))

我甚至试图计算图像rect本身，但在这种情况下，图像在touches begun后消失了

也许我的问题是菜鸟，我可能错过了一些荒谬的东西，但我真的需要弄清楚这一点。

感谢每一个人，祝你有个美好的一天

最好，维克托

答案

天啊...

我刚刚做到了这一点

override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
        if let touch = touches.first as UITouch?{
            let touchPoint = touch.location(in: self.lassoImageView) + lassoOffset!
            print("touch ended at : (touchPoint)")
            erase(fromPoint: touchPoint, toPoint: touchPoint)
            /*UIGraphicsBeginImageContext(lassoImageView.frame.size)
                lassoImageView.image?.draw(in: CGRect(x: 0, y: 0, width: lassoImageView.frame.size.width, height: lassoImageView.frame.size.height), blendMode: .normal, alpha: 1.0)
                lassoImageView.image?.draw(in:  CGRect(x: 0, y: 0, width: lassoImageView.frame.size.width, height: lassoImageView.frame.size.height), blendMode: .normal, alpha: 1.0)
                lassoImageView.image = UIGraphicsGetImageFromCurrentImageContext()
                UIGraphicsEndImageContext()   */
    }

并在我的erase方法改变了这句话：

lassoImageView.image?.draw(in: CGRect(x: 0, y: 0, width: lassoImageView.frame.size.width, height: lassoImageView.frame.size.height))

到这一个：

lassoImageView.layer.render(in: context!)

不确定这里发生了什么，但现在效果很好