Check out example codes for "xcode combine calayer into an image". It will help you in understanding the concepts better.

Code Example 1

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()!

//set finalImage to IBOulet UIImageView
mergeImage.image = newImage

Learn ReactJs, React Native from