docs/design/understanding/understanding.xml


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<?xml version="1.0"?>
<!-- Overview -->
<document>
  <header>
   <title>Understanding FOP Design</title>
   <subtitle>Tutorial series about Design Approach to FOP</subtitle>
   <authors> <person name="Keiron Liddle" email="keiron@aftexsw.com"/>
   </authors>
  </header>
  <body>
<s1 title="Understanding">
      <note>
          The content of this <strong>Understanding series</strong>
          was all taken from the interactive fop development mailing
          list discussion . <br/> We strongly advise you to join this
          mailing list and ask question about this series there. <br/>
          You can subscribe to fop-dev@xml.apache.org by sending an
          email to <link href=
          "mailto:fop-dev-subscribe@xml.apache.org"
          >fop-dev-subscribe@xml.apache.org</link>.  <br/> You will
          find more information about how to get involved <link href=
          "http://xml.apache.org/fop/involved.html"
          >there</link>.<br/> You can also read the <link href=
          "http://marc.theaimsgroup.com/?l=fop-dev&amp;r=1&amp;w=2"
          >archive</link> of the discussion list fop-dev to get an
          idea of the issues being discussed.
      </note>
      <s2 title="Introduction">
        <p>
          Welcome to the understanding series. This will be
          a series of notes for developers to understand how FOP
          works. We will
          attempt to clarify the processes involved to go from xml(fo)
          to pdf or other formats. Some areas will get more
          complicated as we proceed.
        </p>
      </s2>


    <s2 title="Overview">
      <p>FOP takes an xml file does its magic and then writes a document to a
       stream.</p>
      <p>xml -&gt; [FOP] -&gt; document</p>
      <p>The document could be pdf, ps etc. or directed to a printer or the
       screen. The principle remains the same. The xml document must be in the XSL:FO
       format.</p>
      <p>For convenience we provide a mechanism to handle XML+XSL as
       input.</p>
      <p>The xml document is always handled internally as SAX. The SAX events
       are used to read the elements, attributes and text data of the FO document.
       After the manipulation of the data the renderer writes out the pages in the
       appropriate format. It may write as it goes, a page at a time or the whole
       document at once. Once finished the document should contain all the data in the
       chosen format ready for whatever use.</p></s2>
    <s2 title="Stages"><p>The fo data goes through a few stages. Each piece
       of data will generally go through the process in the same way but some
       information may be used a number of times or in a different order. To reduce
       memory one stage will start before the previous is completed.</p>
      <p>SAX Handler -&gt; FO Tree -&gt; Layout Managers -&gt; Area Tree
       -&gt; Render -&gt; document</p>
      <p>In the case of rtf, mif etc. <br/>SAX Handler -&gt; FO Tree -&gt;
       Structure Renderer -&gt; document</p>
      <p>The FO Tree is constructed from the xml document. It is an internal
       representation of the xml document and it is like a DOM with some differences.
       The Layout Managers use the FO Tree do their layout stuff and create an Area
       Tree. The Area Tree is a representation of the final result. It is a
       representation of a set of pages containing the text and other graphics. The
       Area Tree is then given to a Renderer. The Renderer can read the Area Tree and
       convert the information into the render format. For example the PDF Renderer
       creates a PDF Document. For each page in the Area Tree the renderer creates a
       PDF Page and places the contents of the page into the PDF Page. Once a PDF Page
       is complete then it can be written to the output stream.</p>
      <p>For the structure documents the Structure listener will read
       directly from the FO Tree and create the document. These documents do not need
       the layout process or the Area Tree.</p></s2>
    <s2 title="Associated Tasks"><p>Verify Structure Listener
       concept.</p></s2>
    <s2 title="Further Topics">
      <ul><li>XML parsing</li>
       <li>FO Tree</li>
       <li>Properties</li>
       <li>Layout Managers</li>
       <li>Layout Process</li>
       <li>Handling Attributes</li>
       <li>Area Tree</li>
       <li>Renderers</li>
       <li>Images</li>
       <li>PDF Library</li>
       <li>SVG</li>
      </ul>
    </s2>

   </s1>  </body></document>