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I am working on drawing app. I want to implement eraser functionality that erases the path drawn using UIBezierPath.Is it possible??

I have tried below code but its not working 

    UIGraphicsBeginImageContextWithOptions(self.tempImageView.frame.size, false, 0.0)
    if let context = UIGraphicsGetCurrentContext()
    {
        tempImageView.image?.draw(in: CGRect(x:
            0, y: 0, width: self.tempImageView.frame.size.width, height: self.tempImageView.frame.size.height))
        let sublayer = CAShapeLayer()
        self.tempImageView.layer.addSublayer(sublayer)
        context.setBlendMode(CGBlendMode.clear)
        sublayer.strokeColor = editorPanelView.drawingColor.cgColor
        sublayer.lineJoin = kCALineJoinRound
        sublayer.lineCap = kCALineCapRound
        sublayer.lineWidth = editorPanelView.brushWidth
        let path = UIBezierPath()
        path.move(to: CGPoint(x: mid1.x, y: mid1.y))
        path.addQuadCurve(to:CGPoint(x:mid2.x, y:mid2.y) , controlPoint: CGPoint(x: prevPoint1.x, y: prevPoint1.y))
        sublayer.path = path.cgPath
        layerArray.append(sublayer)
        UIGraphicsEndImageContext()
    }

I am not able to find any solution for this. Any help (even if it's just a kick in the right direction) would be appreciated.

blueWings
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1 Answers1

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A CAShapeLayer is a vector drawing. It's shapes. The usual eraser tool works with raster (pixel-based) drawings. The two are different, and there isn't a straightforward way to do an eraser tool on vector drawings.

One way you could do it is to have the eraser tool edit a mask layer which is applied to your shape layer. It would have the effect of erasing the parts of the shape layer where the mask is opaque.

One tricky part to this is that once you've drawn into the mask, you'd have to erase that part of the mask in order for the user to be able to draw new content into the erased area, and that might cause the erased parts of the old drawing to show through.

Getting what you want to do to work well would be quite tricky.

Duncan C
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  • would you mind looking at my attempt at an eraser using the "mask" method you described in this answer and let me know what I am doing wrong? I just want to get the eraser part working, and then I can figure out how to "erase" the "erased" portion to draw into it again. Any help would be great: https://stackoverflow.com/questions/57381552/how-to-create-an-eraser-for-calayer-sublayer-using-a-cashapelayer-in-swift – jforward5 Sep 08 '19 at 20:29