Union UIBezierPaths rather than apend path - ios

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

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.

Answer 3

You can use the GPCPolygon, an Objective-C wrapper for GPC
-GPCPolygonSet*) initWithPolygons:(NSMutableArray*)points;
or
- (GPCPolygonSet*) unionWithPolygonSet:(GPCPolygonSet*)p2;