iOS UIImage生成高性能圆角图片

• (void)imageWihtSize:(CGSize)size radius:(CGFloat)radius backColor:(UIColor *)backColor completion:(void(^)(UIImage *image))completion{
  // 异步绘制裁切
  dispatch_async(dispatch_get_global_queue(0, 0), ^{
  // 利用绘图建立上下文
  UIGraphicsBeginImageContextWithOptions(size, true, 0);
  CGRect rect = CGRectMake(0, 0, size.width, size.height);
  // 填充颜色
  [backColor setFill];
  UIRectFill(rect);
  // 贝塞尔裁切
  UIBezierPath *path = [UIBezierPath bezierPathWithRoundedRect:rect cornerRadius:radius];
  [path addClip];
  [self drawInRect:rect];

    // 获取结果
    UIImage *resultImage = UIGraphicsGetImageFromCurrentImageContext();
    // 关闭上下文
    UIGraphicsEndImageContext();
    // 主队列回调
    dispatch_async(dispatch_get_main_queue(), ^{
        completion(resultImage);
    });
  

  });
  }

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