// 2D绘图  Quartz2D

// 合并图片 -- 水印

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event

{

    // 1.队列组

    dispatch_group_t group = dispatch_group_create();

    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, );

    // 2.下载图片1

    __block UIImage *image1 = nil;

    dispatch_group_async(group, queue, ^{

        NSURL *url1 = [NSURL URLWithString:@"http://g.hiphotos.baidu.com/image/pic/item/f2deb48f8c5494ee460de6182ff5e0fe99257e80.jpg"];

        NSData *data1 = [NSData dataWithContentsOfURL:url1];

        image1 = [UIImage imageWithData:data1];

    });

    // 3.下载图片2

    __block UIImage *image2 = nil;

    dispatch_group_async(group, queue, ^{

        NSURL *url2 = [NSURL URLWithString:@"http://su.bdimg.com/static/superplus/img/logo_white_ee663702.png"];

        NSData *data2 = [NSData dataWithContentsOfURL:url2];

        image2 = [UIImage imageWithData:data2];

    });

    // 4.合并图片 (保证执行完组里面的所有任务之后，再执行notify函数里面的block)

    dispatch_group_notify(group, queue, ^{

        // 开启一个位图上下文

        UIGraphicsBeginImageContextWithOptions(image1.size, NO, 0.0);

        // 绘制第1张图片

        CGFloat image1W = image1.size.width;

        CGFloat image1H = image1.size.height;

        [image1 drawInRect:CGRectMake(, , image1W, image1H)];

        // 绘制第2张图片

        CGFloat image2W = image2.size.width * 0.5;

        CGFloat image2H = image2.size.height * 0.5;

        CGFloat image2Y = image1H - image2H;

        [image2 drawInRect:CGRectMake(, image2Y, image2W, image2H)];

        // 得到上下文中的图片

        UIImage *fullImage = UIGraphicsGetImageFromCurrentImageContext();

        // 结束上下文

        UIGraphicsEndImageContext();

        // 5.回到主线程显示图片

        dispatch_async(dispatch_get_main_queue(), ^{

            self.imageView.image = fullImage;

        });

    });

}