Quartz2D-圆形图片剪切

实现流程：在上下文绘制一个剪切后的圆；然后再将图片绘制上去；最后通过从上下文中取出这张图片

//加载剪切图片
    UIImage *image = [UIImage imageNamed:@"阿狸头像"];
    //1.获取上下文
    UIGraphicsBeginImageContextWithOptions(image.size, NO, 0);
    
    //2.绘制剪切路径----圆
    UIBezierPath *path = [UIBezierPath bezierPathWithOvalInRect:CGRectMake(0, 0, image.size.width, image.size.height)];
    [path addClip];
    
    //3.绘制图片
    [image drawAtPoint:CGPointZero];
    
    //4.从上下文中取出剪切后的图片
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    
    //5.关闭上下文
    UIGraphicsEndImageContext();
    
    self.imageView.image = newImage;