Swift4でUIImageの反転

##実装コード

UIImage+flip.swift

import UIKit

extension UIImage {

    let scale = 1.0

    //上下反転
    func flipVertical() -> UIImage {
        UIGraphicsBeginImageContextWithOptions(size, false, scale)
        let imageRef = self.cgImage
        let context = UIGraphicsGetCurrentContext()
        context?.translateBy(x: 0, y:  0)
        context?.scaleBy(x: 1.0, y: 1.0)
        context?.draw(imageRef!, in: CGRect(x: 0, y: 0, width: size.width, height: size.height))
        let flipHorizontalImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return flipHorizontalImage!
    }

    //左右反転
    func flipHorizontal() -> UIImage {
        UIGraphicsBeginImageContextWithOptions(size, false, scale)
        let imageRef = self.cgImage
        let context = UIGraphicsGetCurrentContext()
        context?.translateBy(x: size.width, y:  size.height)
        context?.scaleBy(x: -1.0, y: -1.0)
        context?.draw(imageRef!, in: CGRect(x: 0, y: 0, width: size.width, height: size.height))
        let flipHorizontalImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return flipHorizontalImage!
    } 

}

##使用方法

extensionで実装していますので以下のように呼び出せます。

let flipImage = image.flipVertical()
let flipImage = image.flipHorizontal()