xcode combine calayer into an image
let topImage = UIImage(named: "image1.png")
let bottomImage = UIImage(named: "image2.png")
let size = CGSize(width: topImage!.size.width, height: topImage!.size.height + bottomImage!.size.height)
UIGraphicsBeginImageContextWithOptions(size, false, 0.0)
topImage!.draw(in: CGRect(x: 0, y: 0, width: size.width, height: topImage!.size.height))
bottomImage!.draw(in: CGRect(x: 0, y: topImage!.size.height, width: size.width, height: bottomImage!.size.height))
let newImage:UIImage = UIGraphicsGetImageFromCurrentImageContext()!
UIGraphicsEndImageContext()
//set finalImage to IBOulet UIImageView
mergeImage.image = newImage