iOS图片添加水印，给水印添加背景

做需求的时候，发现有需要给图片水印添加背景颜色的，搜了好久，没有找到需要的例子，试了下通过view去调用drawInRect方法行不通，自己摸索下用画布填充的方式ok了，记录一下。

UIImage *imageAddBgText(UIImage *img, NSString *mark) {
   UIImage *newImage = [MTImageCompressHelper imageCompressForWidth:img targetWidth:720];
    
    int imgWidth = newImage.size.width;
    int imgHeight = newImage.size.height;
    
    UIGraphicsBeginImageContext(newImage.size);
    [[UIColor redColor] set];
    [newImage drawInRect:CGRectMake(0, 0, imgWidth, imgHeight)];
    CGFloat textH = heightForString(mark, 24, imgWidth, 0);
    CGRect bgFrame = CGRectMake(0, imgHeight-textH-20, imgWidth, textH+20);
    CGRect markFrame = CGRectMake(10, imgHeight-textH-10, imgWidth-20, textH);
    //画布填充方法begin
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetFillColorWithColor(context, UIColor.whiteColor.CGColor);
    CGContextFillRect(context, bgFrame);
    //画布填充方法 end
    [mark drawInRect:markFrame withAttributes:@{NSFontAttributeName:[UIFont systemFontOfSize:24],NSForegroundColorAttributeName:[UIColor redColor]}];
    UIImage *imageRet = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    
    imageRet = [MTImageCompressHelper compressedImageToLimitSizeOfKB:300 image:imageRet];
    return imageRet;
}