合并两个UIImages

func mergeImages(image1: UIImage, image2: UIImage) -> UIImage? {
    let size = CGSize(width: image1.size.width, height: image1.size.height + image2.size.height)
    
    UIGraphicsBeginImageContextWithOptions(size, false, 0.0)
    
    image1.draw(in: CGRect(x: 0, y: 0, width: size.width, height: image1.size.height))
    image2.draw(in: CGRect(x: 0, y: image1.size.height, width: size.width, height: image2.size.height))
    
    let mergedImage = UIGraphicsGetImageFromCurrentImageContext()
    
    UIGraphicsEndImageContext()
    
    return mergedImage
}