Union UIBezierPaths rather than apend path

Question

I have an app where I take a UIBezierPath and use it as a brush by a series of appendPath: calls. After a few goes and with really complex brush shapes the memory runs out and the app grinds to a halt. What I really want to do is a full on union exactly like Paint Code does but I can't find any way of doing this.

How would I go about unioning two or more UIBezierPaths?

EDIT:

Here is a visual of what I want to achieve dynamically.

In Paint Code you take two paths and overlap them like this:

BUT I want to merge / union them into one new single path like:

Note that in the bottom panel of Paint Code there is code for now one single shape and this is what I want to be able to get to programatically with maybe 1000 original paths.

Answer 1

You can get desired result easily by following 2 concepts of Core Graphics :-

i)CGBlendMode ii)OverLap2Layer

Blend modes tell a context how to apply new content to itself. They determine how pixel data is digitally blended.

 class UnionUIBezierPaths : UIView {

    var firstBeizerPath:UIImage!
    var secondBeizerPath:UIImage!

    override func draw(_ rect: CGRect) {
        super.draw(rect)

       firstBeizerPath = drawOverLapPath(firstBeizerpath: drawCircle(), secondBeizerPath: polygon())
       secondBeizerPath = drawOverLapPath(firstBeizerpath: polygon(), secondBeizerPath: drawCircle())

        let image = UIImage().overLap2Layer(firstLayer:firstBeizerPath , secondLayer:secondBeizerPath)
    }


    func drawCircle() -> UIBezierPath {
        let path = UIBezierPath(ovalIn: CGRect(x: 40, y: 120, width: 100, height: 100) )
        return path
    }

    func polygon() -> UIBezierPath {
        let beizerPath = UIBezierPath()
        beizerPath.move(to: CGPoint(x: 100, y: 10) )
        beizerPath.addLine(to: CGPoint(x: 200.0, y: 40.0) )
        beizerPath.addLine(to: CGPoint(x: 160, y: 140) )
        beizerPath.addLine(to: CGPoint(x: 40, y: 140) )
        beizerPath.addLine(to: CGPoint(x: 0, y: 40) )
        beizerPath.close()
        return beizerPath
    }

    func drawOverLapPath(firstBeizerpath:UIBezierPath ,secondBeizerPath:UIBezierPath )  -> UIImage {

        UIGraphicsBeginImageContext(self.frame.size)

        let firstpath = firstBeizerpath
        UIColor.white.setFill()
        UIColor.black.setStroke()
        firstpath.stroke()
        firstpath.fill()

        // sourceAtop = 20
        let mode = CGBlendMode(rawValue:20)
        UIGraphicsGetCurrentContext()!.setBlendMode(mode!)


        let secondPath = secondBeizerPath
        UIColor.white.setFill()
        UIColor.white.setStroke()
        secondPath.fill()
        secondPath.stroke()

        let image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()

        return image!
    }



    func drawImage(image1:UIImage , secondImage:UIImage ) ->UIImage
    {
        UIGraphicsBeginImageContext(self.frame.size)
        image1.draw(in: CGRect(x: 0, y: 0, width: frame.size.width, height: frame.size.height) )
        secondImage.draw(in: CGRect(x: 0, y: 0, width: frame.size.width, height: frame.size.height) )

        let newImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return newImage!
    }

      }

      //OverLap2Layer
      extension UIImage {
      func overLap2Layer(firstLayer:UIImage , secondLayer:UIImage ) -> UIImage {

                UIGraphicsBeginImageContext(firstLayer.size)
                firstLayer.draw(in: CGRect(x: 0, y: 0, width: firstLayer.size.width, height: firstLayer.size.height) )
                secondLayer.draw(in: CGRect(x: 0, y: 0, width: firstLayer.size.width, height: firstLayer.size.height) )

                let newImage = UIGraphicsGetImageFromCurrentImageContext()
                UIGraphicsEndImageContext()
                return newImage!
            }
        }

First Path :-

Second Path :-

Final Result :-

Reference:- Blend in Core Graphics , Creating Image

GitHub Demo

Answer 2

You can use the GPCPolygon, an Objective-C wrapper for GPC

-GPCPolygonSet*) initWithPolygons:(NSMutableArray*)points;

or

- (GPCPolygonSet*) unionWithPolygonSet:(GPCPolygonSet*)p2;

Answer 3

Finally a solution!!

Using https://github.com/adamwulf/ClippingBezier you can find the intersecting points. Then you can walk through the path, turning left if clockwise or vice-versa to stay on the outside. Then you can generate a new path using the sequence of points.