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Resolve CSS Images in Output TBB

This week's TBB is Resolve CSS Images in Output TBB. This template identifies unresolved image references inside CSS selectors "background: url('tcm:x-yy')", publishes the MMC and replaces the reference with the resolved URL.

I got this TBB from my colleague Eric Huiza, so he gets the credit for it ;)

Render Css Images In Output TBB
·    Template in .NET Assembly
Used to:
·    Resolve references to Multimedia Components TcmUris inside CSS syntax;
·    Publish the MMC and replace the TcmUri reference with the resolved URL;
This generic TBB uses the Output item to search for references to MMC TcmUris (or WebDav URLs) inside CSS ‘background’ selectors.
If such MMC TcmUri is identified, the MMC is published (to the mapped Structure Group) and the returned URL replaces the TcmUri reference.
The Output item is rewritten with the resolved URLs.
Applicable to
Any template where an Item called ‘Output’ exists in the Package

The Code

[TcmTemplateTitle("Resolve Css Images In Output TBB")]
public class ResolveCssImagesInOutput : ITemplate {

    private const string CSS_IMG_REG_EX = @"background(-image)?:(\s)*(transparent)?(\s)*(url[\s]*\([\s]*(?<url>[^\)]*)[\s]*\)[\s]*)+";
    private readonly Regex cssImgRegEx = new Regex(CSS_IMG_REG_EX, RegexOptions.IgnoreCase);

    public void Transform(Engine engine, Package package) {
        GenericUtils utils = new GenericUtils();
        Item outputItem = package.GetByName(Package.OutputName);
        string css = outputItem.GetAsString();

        foreach (Match match in GetBackgroundEntities(css)) {
            string uri = match.Groups["url"].Value.Replace("\"", string.Empty).Replace("'", string.Empty);
            string localUri = utils.LocalizeUri(engine, uri);
            Component imgComponent = engine.GetObject(localUri) as Component;
            if (imgComponent != null) {
                Binary binary = utils.PublishBinary(engine, package, imgComponent);
                css = css.Replace(uri, binary.Url);


    private IEnumerable<Match> GetBackgroundEntities(string css) {
        return cssImgRegEx.Matches(css).Cast<Match>().
            Where(w => w.Groups["url"].Value.StartsWith("\"/webdav") ||
                w.Groups["url"].Value.StartsWith("'/webdav") ||
                w.Groups["url"].Value.Contains("\"tcm:") ||


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