This and that of Core Graphics

UIImage+CoreGraphics.swift

import UIKit

extension UIImage {

  //Preparation
  private func preprare(size: CGSize, _ draw: (() -> Void)? = nil) -> UIImage! {
    UIGraphicsBeginImageContextWithOptions(size, true, 0)

    draw?()

    let newImage = UIGraphicsGetImageFromCurrentImageContext()

    UIGraphicsEndImageContext()

    return newImage
  }

  func resize(ratio: CGFloat) -> UIImage! {
    let size = CGSize(width: self.size.width * ratio, height: self.size.height * ratio)
    return self.resize(size: size)
  }

  func resize(height: CGFloat) -> UIImage! {
    let width = self.size.width * height / self.size.height
    let size = CGSize(width: width, height: height)
    return self.resize(size: size)
  }

  func resize(width: CGFloat) -> UIImage! {
    let height = self.size.height * width / self.size.width
    let size = CGSize(width: width, height: height)
    return self.resize(size: size)
  }

  func resize(size: CGSize) -> UIImage! {
    preprare(size: size) {
      self.draw(in: CGRect(x: 0, y: 0, width: size.width, height: size.height))
    }
  }

  func compose(image: UIImage, frame: CGRect) -> UIImage! {
    preprare(size: self.size) {
      self.draw(at: .zero)
      image.draw(in: frame)
    }
  }

  func compose(image: UIImage, atCenter: CGPoint, blendMode: CGBlendMode = .copy, alpha: CGFloat = 1.0) -> UIImage! {
    preprare(size: self.size) {
      self.draw(at: .zero)
      let at = CGPoint(x: atCenter.x - image.size.width/2, y: atCenter.y - image.size.height/2)
      image.draw(at: at, blendMode: blendMode, alpha: alpha)
    }
  }

  func compose(image: UIImage, at: CGPoint, blendMode: CGBlendMode = .copy, alpha: CGFloat = 1.0) -> UIImage! {
    preprare(size: self.size) {
      self.draw(at: .zero)
      image.draw(at: at, blendMode: blendMode, alpha: alpha)
    }
  }
}