Example: Creating a simple PDF plug-in

This scenario walks through the process of creating a very simple plug-in (com.example.print-pdf) that creates a new transformation type: print-pdf.

About this task

The print-pdf transformation has the following characteristics:

  • Uses A4 paper
  • Renders figures with a title at the top and a description at the bottom
  • Use em dashes as the symbols for unordered lists

Procedure

  1. In the plugins directory, create a directory named com.example.print-pdf.
  2. In the new com.example.print-pdf directory, create a plug-in configuration file (plugin.xml) that declares the new print-pdf transformation and its dependencies.
    Figure 1. plugin.xml file
    <?xml version='1.0' encoding='UTF-8'?>
    <plugin id="com.example.print-pdf">
      <require plugin="org.dita.pdf2"/>
      <feature extension="dita.conductor.transtype.check" 
               value="print-pdf"/>
      <feature extension="dita.transtype.print" value="print-pdf"/>
      <feature extension="dita.conductor.target.relative" 
               file="integrator.xml"/>
    </plugin>
  3. Add an Ant script (integrator.xml) to define the transformation type.
    Figure 2. integrator.xml file
    <?xml version='1.0' encoding='UTF-8'?>
    <project name="com.example.print-pdf">
      <target name="dita2print-pdf.init">
        <property name="customization.dir" 
         location="${dita.plugin.com.example.print-pdf.dir}/cfg"/></target>
      <target name="dita2print-pdf" 
              depends="dita2print-pdf.init, dita2pdf2"/>
    </project>
  4. In the new plug-in directory, add a cfg/catalog.xml file that specifies the custom XSLT style sheets.
    Figure 3. cfg/catalog.xml file
    <?xml version="1.0" encoding="UTF-8"?>
    <catalog prefer="system" 
             xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog">
      <uri name="cfg:fo/attrs/custom.xsl" uri="fo/attrs/custom.xsl"/>
      <uri name="cfg:fo/xsl/custom.xsl" uri="fo/xsl/custom.xsl"/>
    </catalog>
  5. Create the cfg/fo/attrs/custom.xsl file, and add attribute and variable overrides to it.
    For example, add the content highlighted with bold to change the page size to A4.
    Figure 4. cfg/fo/attrs/custom.xsl file
    <?xml version="1.0" encoding="UTF-8"?>
    <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                    version="2.0">
      <!-- Change page size to A4 -->
      <xsl:variable name="page-width">210mm</xsl:variable>
      <xsl:variable name="page-height">297mm</xsl:variable>
    </xsl:stylesheet>
  6. Create the cfg/fo/xsl/custom.xsl file, and add XSLT overrides to it.
    For example, the following code changes the rendering of <figure> elements.
    Figure 5. cfg/fo/xsl/custom.xsl file
    <?xml version="1.0" encoding="UTF-8"?>
    <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                    xmlns:xs="http://www.w3.org/2001/XMLSchema"
                    xmlns:fo="http://www.w3.org/1999/XSL/Format"
                    version="2.0">
      <!-- Move figure title to top and description to bottom -->
      <xsl:template match="*[contains(@class,' topic/fig ')]">
        <fo:block xsl:use-attribute-sets="fig">
          <xsl:call-template name="commonattributes"/>
          <xsl:if test="not(@id)">
            <xsl:attribute name="id">
              <xsl:call-template name="get-id"/>
            </xsl:attribute>
          </xsl:if>
          <xsl:apply-templates select="*[contains(@class,' topic/title ')]"/>
          <xsl:apply-templates select="*[not(contains(@class,' topic/title ') or contains(@class,' topic/desc '))]"/>
          <xsl:apply-templates select="*[contains(@class,' topic/desc ')]"/>
        </fo:block>
      </xsl:template>
    </xsl:stylesheet>
  7. Create an English-language variable-definition file (cfg/common/vars/en.xml) and make any necessary modifications to it.
    For example, the following code removes the period after the number for an ordered-list item; it also specifies that the bullet for an unordered list item should be an em dash.
    Figure 6. cfg/common/vars/en.xml file
    <?xml version="1.0" encoding="UTF-8"?>
    <vars xmlns="http://www.idiominc.com/opentopic/vars">
      <!-- Remove dot from list number -->
      <variable id="Ordered List Number">
        <param ref-name="number"/>
      </variable>
      <!-- Change unordered list bullet to an em dash -->
      <variable id="Unordered List bullet">&#x2014;</variable>
    </vars>

Results

The new plug-in directory has the following layout and files:

com.example.print-pdf/
  cfg/
    common/
      vars/
        en.xml
    fo/
      attrs/
        custom.xsl
      xsl/
        custom.xsl
    catalog.xml
  integrator.xml
  plugin.xml

What to do next

Run dita-ot-dir/bin/dita --install to install the plug-in and make the print-pdf transformation available.