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<h1>Events</h1>
<p>
Sometimes you'd want to add your own code to the rendering routines; for example, you could want to make your own watermarks, 
count pages in the multiple-document batch, add digital signature to the generated PDF file or 
perform any other actions requiring low-level access to PDF file at the certain moments. Now you may do this using 
HTML2PS events. Pipeline object will fire events at predefined moments while rendering PDF file; you may catch them and 
do something useful.
</p>

<p>The code below illustrates installation of a simple callback to be called immediately after 
new page was rendered. (If you're using PHP 5, you can write this way more elegant, but we're keeping PHP 4 compatibility here)</p>
<pre>
$dispatcher =& $pipeline->get_dispatcher();
$dispatcher->add_observer('after-page', 'my_watermark_callback_func');
</pre>

<p>
A single parameter is passed to the callback function: an associative array containing information related to event. 
</p>

<p>Following events are available:</p>
<table>
<thead>
<tr>
<th>Name</th>
<th>Fired&hellip;</th>
<th>Event information</th>
</tr>
</thead>
<tbody>
<tr>
<td class="event-name">after-batch</td>
<td>after all documents in current batch were rendered</td>
<td>pipeline: reference to current pipeline object</td>
</tr>
<tr>
<td class="event-name">after-batch-item</td>
<td>after current batch item was processed, rendered and removed from the memory</td>
<td>pipeline: reference to current pipeline object</td>
</tr>
<tr>
<td class="event-name">after-document</td>
<td>after all pages in a current document were rendered</td>
<td>pipeline: reference to current pipeline object; document: reference to the body box object</td>
</tr>
<tr>
<td class="event-name">after-page</td>
<td>after all elements were rendered on current page, but before new page is added.</td>
<td>pipeline: reference to current pipeline object; document: reference to the body box object; pageno: current page number (1-based)</td>
</tr>
<tr>
<td class="event-name">after-parse</td>
<td>Called immediately after XML parser but before any tree filters</td>
<td>pipeline: reference to current pipeline object; document: reference to the body box object; media: reference the current output media object.</td>
</tr>
<tr>
<td class="event-name">before-batch</td>
<td>before new document batch starts rendering</td>
<td>pipeline: reference to current pipeline object</td>
</tr>
<tr>
<td class="event-name">before-batch-item</td>
<td>just before current batch item is fetched</td>
<td>pipeline: reference to current pipeline object</td>
</tr>
<tr>
<td class="event-name">before-document</td>
<td>before new document in a batch starts rendering</td>
<td>pipeline: reference to current pipeline object; document: reference to the body box object; page-heights: array of page heights (measured in points) for this document</td>
</tr>
<tr>
<td class="event-name">before-page</td>
<td>after new blank page is added to the PDF document but before any elements are rendered</td>
<td>pipeline: reference to current pipeline object; document: reference to the body box object; pageno: current page number (1-based)</td>
</tr>
<tr>
<td class="event-name">before-page-heights</td>
<td>after content has been laid out, just before running the page breaking algorithm</td>
<td>pipeline: reference to current pipeline object; document: reference to the body box object; media: reference the current output media object.</td>
</tr>
</tbody>
</table>

<h2>Event usage</h2>
<p>
A nice sample of events usage was contributed by <b>marco_snake</b> on tufat html2ps/pdf community forum. In this sample, 
events are used to display specific HTML code only on pages with predefined numbers.
PHP and HTML code is available in <tt>samples/API/events/1</tt> directory in the distribution package.
</p>

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