需求是连接打印机，将文本内容生成图片然后裁剪之后传输给打印机打印。生成图片之后效果

大概原理是拿到View的上下文的范围，然后根据上下文生成图片
核心代码

     /*
         self.makeView   视图
         self.all  整体获取视图显示ImageView
         self.part  裁剪之后图片显示ImageView
     */
    //获取上下文范围
    UIGraphicsBeginImageContext(self.makeView.bounds.size);
    //呈现
    [self.makeView.layer renderInContext:UIGraphicsGetCurrentContext()];
    //根据当前上下文生成图片
    UIImage *allImage = UIGraphicsGetImageFromCurrentImageContext();
    
    CGRect rect = CGRectMake(0, 0, 30, 10);
    //根据CGRect裁剪图片
    UIImage *partImage = [UIImage imageWithCGImage:CGImageCreateWithImageInRect(allImage.CGImage, rect)];
    //释放
    UIGraphicsEndImageContext();
    self.all.image = allImage;
    self.part.image = partImage;