swift3.0之代码裁剪图片（只显示部分图片）

let image = UIImage()

            //获取图片过程省略

let rect = CGRect(x: 50, y: 50, width: 50, height: 50)

let cgImageCorpped = image.cgImage?.cropping(to: rect)

let imageCorpped = UIImage(cgImage: cgImageCorpped!)