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<!DOCTYPE document PUBLIC "-//APACHE//DTD Documentation V2.0//EN" "http://forrest.apache.org/dtd/document-v20.dtd">
<document>
  <header>
    <title>Intermediate Format</title>
    <version>$Revision$</version>
  </header>
  <body>
    <note>
      Please note that the intermediate format is an <strong>advanced feature</strong> and can be ignored by most
      users of Apache FOP.
    </note>
    <section id="introduction">
      <title>Introduction</title>
      <p>
        The intermediate format (IF) is a proprietary XML format that represents the area tree 
        generated by the layout engine. The area tree is conceptually defined in the 
        <a href="http://www.w3.org/TR/xsl/slice1.html#section-N742-Formatting">XSL-FO specification in chapter 1.1.2</a>.
        The IF can be generated through the area tree XML Renderer (the XMLRenderer).
      </p>
      <p>
        The intermediate format can be used to generate intermediate documents that are modified 
        before they are finally rendered to their ultimate output format. Modifications include
        adjusting and changing trait values, adding or modifying area objects, inserting prefabricated
        pages, overlays, imposition (n-up, rotation, scaling etc.). Multiple IF files can be combined
        to a single output file.
      </p>
    </section>
    <section id="usage">
      <title>Usage of the Intermediate Format</title>
      <p>
        As already mentioned, the IF is generated by using the <strong>XMLRenderer</strong> (MIME type: 
        <strong>application/X-fop-areatree</strong>). So, you basically set the right MIME type for
        the output format and process your FO files as if you would create a PDF file. However, there
        is an important detail to consider: The various Renderers don't all use the same font sources.
        To be able to create the right area tree for the ultimate output file, you need to create
        the IF file using the right font setup. This is achieved by telling the XMLRenderer to mimic
        another renderer. This is done by calling the XMLRenderer's mimicRenderer() method with an
        instance of the ultimate target renderer as the single parameter. This has a consequence: An
        IF file rendered with the Java2DRenderer may not look as expected when it was actually generated
        for the PDF renderer. For renderers that use the same font setup, this restriction does not
        apply (PDF and PS, for example). Generating the intermediate format file is the first step.
      </p>
      <p>
        The second step is to reparse the IF file using the <strong>AreaTreeParser</strong> which is 
        found in the org.apache.fop.area package. The pages retrieved from the IF file are added to an
        AreaTreeModel instance from where they are normally rendered using one of the available Renderer
        implementations. You can find examples for the IF processing in the 
        <a href="http://svn.apache.org/viewcvs.cgi/xmlgraphics/fop/trunk/examples/embedding/java/embedding/intermediate/"><code>examples/embedding</code></a>
        directory in the FOP distribution
      </p>
      <p>
        The basic pattern to parse the IF format looks like this:
      </p>
      <source><![CDATA[
// Setup output
OutputStream out = new java.io.FileOutputStream(pdffile);
out = new java.io.BufferedOutputStream(out);
try {
    //Setup fonts and user agent
    FontInfo fontInfo = new FontInfo();
    FOUserAgent userAgent = new FOUserAgent();

    //Construct the AreaTreeModel that will received the individual pages
    AreaTreeModel treeModel = new RenderPagesModel(userAgent, 
            MimeConstants.MIME_PDF, fontInfo, out);
            
    //Parse the IF file into the area tree
    AreaTreeParser parser = new AreaTreeParser();
    Source src = new StreamSource(myIFFile);
    parser.parse(src, treeModel, userAgent);
            
    //Signal the end of the processing. The renderer can finalize the target document.
    treeModel.endDocument();
} finally {
    out.close();
}]]></source>
      <p>
        This example simply reads an IF file and renders it to a PDF file. Please note, that in normal
        FOP operation you're shielded from having to instantiate the FontInfo object yourself. This
        is normally a task of the AreaTreeHandler which is not present in this scenario. The same
        applies to the AreaTreeModel instance, in this case an instance of a subclass called 
        RenderPagesModel. RenderPagesModel is ideal in this case as it has very little overhead 
        processing the individual pages. An important line in the example is the call to 
        <code>endDocument()</code> on the AreaTreeModel. This lets the Renderer know that the processing
        is now finished.
      </p>
      <p>
        The intermediate format can also be used from the <a href="running.html#standalone-start">command-line</a>
        by using the "-atin" parameter for specifying the area tree XML as input file. You can also 
        specify a "mimic renderer" by inserting a MIME type between "-at" and the output file.
      </p>
      <section id="concat">
        <title>Concatenating Documents</title>
        <p>
          This initial example is obviously not very useful. It would be faster to create the PDF file 
          directly. As the <a href="http://svn.apache.org/repos/asf/xmlgraphics/fop/trunk/examples/embedding/java/embedding/intermediate/ExampleConcat.java">ExampleConcat.java</a>
          example shows you can easily parse multiple IF files in a row and add the parsed pages to the
          same AreaTreeModel instance which essentially concatenates all the input document to one single
          output document.
        </p>
      </section>
      <section id="modifying">
        <title>Modifying Documents</title>
        <p>
          One of the most important use cases for the intermediate format is obviously modifying the area
          tree XML before finally rendering it to the target format. You can easily use XSLT to process
          the IF file according to your needs. Please note, that we will currently not formally describe
          the intermediate format. You need to have a good understanding its structure so you don't
          create any non-parseable files. We may add an XML Schema and more detailed documentation at a
          later time. You're invited to help us with that.
        </p>
      </section>
      <section id="advanced">
        <title>Advanced Use</title>
        <p>
          The generation of the intermediate format as well as it parsing process has been designed to allow
          for maximum flexibility and optimization. Please note that you can call <code>setTransformerHandler()</code> on
          XMLRenderer to give the XMLRenderer your own TransformerHandler instance in case you would like to
          do custom serialization (to a W3C DOM, for example) and/or to directly modify the area tree using 
          XSLT. The AreaTreeParser on the other side allows you to retrieve a ContentHandler instance where
          you can manually send SAX events to to start the parsing process (see <code>getContentHandler()</code>).
        </p>
      </section>
    </section>
  </body>
</document>