Quartz2D 给图片打水印

 1 + (instancetype)waterImageWithBg:(NSString *)bg logo:(NSString *)logo {
 2     UIImage *oldImage = [UIImage imageNamed:bg];
 3     // 1.创建一个基于位图（bitmap）的上下文（开启一个基于位图的上下文）
 4     // size：新图片的尺寸
 5     // opaque：YES：不透明，NO：透明
 6     // 这行代码过后，相当于创建一张新的bitmap，也就是新的UIImage对象
 7     UIGraphicsBeginImageContextWithOptions(oldImage.size, NO, 0.0);
 8     // 2.画背景
 9     [oldImage drawInRect:CGRectMake(0, 0, oldImage.size.width, oldImage.size.height)];
10     // 3.画水印
11     UIImage *image = [UIImage imageNamed:logo];
12 
13     CGFloat scale = 0.5; // 按比例缩小图片
14     CGFloat logoW = image.size.width * scale;
15     CGFloat logoH = image.size.height * scale;
16     CGFloat logoX = oldImage.size.width - logoW;
17     CGFloat logoY = oldImage.size.height - logoH;
18     [image drawInRect:CGRectMake(logoX, logoY, logoW, logoH)];
19     // 4.从上下文中获取制作完毕的UIImage对象
20     UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
21 
22     // 5.结束上下文
23     UIGraphicsEndImageContext();
24     return newImage;
25 }

    // 6.将image对象压缩成png格式的二进制数据
    NSData *data = UIImagePNGRepresentation(image);
    // 7.获得沙盒路径，写入文件
    NSString *documentPath = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent:@"lufei.png"];
    [data writeToFile:documentPath atomically:YES];