iOS 多张图片合成

func imageSynthesis(_ arguments: [(UIImage, CGRect)], _ size: CGSize) -> UIImage {
    
    UIGraphicsBeginImageContext(size);
    
    for (image, rect) in arguments {
        image.draw(in: rect)
    }
    
    guard let resultImage = UIGraphicsGetImageFromCurrentImageContext() else { return UIImage() }
    UIGraphicsEndImageContext()
    
    return resultImage;
}