CGPoint extension for SpriteKit

Point.swift

extension CGPoint {
    
    public enum CoordinateSystem {
        case UIKit
        case SpriteKit
    }
    
    public func coordinates(from from: CoordinateSystem, to: CoordinateSystem) -> CGPoint {
        if from == to { return self }
        else  {
            return CGPoint(x: self.x, y: -self.y)
        }
    }
}

public func +(lhs: CGPoint, rhs: CGPoint) -> CGPoint {
    return CGPoint(x: lhs.x + rhs.x, y: lhs.y + rhs.y)
}

public func -(lhs: CGPoint, rhs: CGPoint) -> CGPoint {
    return CGPoint(x: lhs.x - rhs.x, y: lhs.y - rhs.y)
}

public func +=(inout lhs: CGPoint, rhs: CGPoint) {
    lhs = lhs + rhs
}

public func -=(inout lhs: CGPoint, rhs: CGPoint) {
    lhs = lhs - rhs
}