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3<title>Events</title>
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31<h1>Events</h1>
32<p>
33Sometimes you'd want to add your own code to the rendering routines; for example, you could want to make your own watermarks,
34count pages in the multiple-document batch, add digital signature to the generated PDF file or
35perform any other actions requiring low-level access to PDF file at the certain moments. Now you may do this using
36HTML2PS events. Pipeline object will fire events at predefined moments while rendering PDF file; you may catch them and
37do something useful.
38</p>
39
40<p>The code below illustrates installation of a simple callback to be called immediately after
41new 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>
42<pre>
43$dispatcher =& $pipeline->get_dispatcher();
44$dispatcher->add_observer('after-page', 'my_watermark_callback_func');
45</pre>
46
47<p>
48A single parameter is passed to the callback function: an associative array containing information related to event.
49</p>
50
51<p>Following events are available:</p>
52<table>
53<thead>
54<tr>
55<th>Name</th>
56<th>Fired&hellip;</th>
57<th>Event information</th>
58</tr>
59</thead>
60<tbody>
61<tr>
62<td class="event-name">after-batch</td>
63<td>after all documents in current batch were rendered</td>
64<td>pipeline: reference to current pipeline object</td>
65</tr>
66<tr>
67<td class="event-name">after-batch-item</td>
68<td>after current batch item was processed, rendered and removed from the memory</td>
69<td>pipeline: reference to current pipeline object</td>
70</tr>
71<tr>
72<td class="event-name">after-document</td>
73<td>after all pages in a current document were rendered</td>
74<td>pipeline: reference to current pipeline object; document: reference to the body box object</td>
75</tr>
76<tr>
77<td class="event-name">after-page</td>
78<td>after all elements were rendered on current page, but before new page is added.</td>
79<td>pipeline: reference to current pipeline object; document: reference to the body box object; pageno: current page number (1-based)</td>
80</tr>
81<tr>
82<td class="event-name">after-parse</td>
83<td>Called immediately after XML parser but before any tree filters</td>
84<td>pipeline: reference to current pipeline object; document: reference to the body box object; media: reference the current output media object.</td>
85</tr>
86<tr>
87<td class="event-name">before-batch</td>
88<td>before new document batch starts rendering</td>
89<td>pipeline: reference to current pipeline object</td>
90</tr>
91<tr>
92<td class="event-name">before-batch-item</td>
93<td>just before current batch item is fetched</td>
94<td>pipeline: reference to current pipeline object</td>
95</tr>
96<tr>
97<td class="event-name">before-document</td>
98<td>before new document in a batch starts rendering</td>
99<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>
100</tr>
101<tr>
102<td class="event-name">before-page</td>
103<td>after new blank page is added to the PDF document but before any elements are rendered</td>
104<td>pipeline: reference to current pipeline object; document: reference to the body box object; pageno: current page number (1-based)</td>
105</tr>
106<tr>
107<td class="event-name">before-page-heights</td>
108<td>after content has been laid out, just before running the page breaking algorithm</td>
109<td>pipeline: reference to current pipeline object; document: reference to the body box object; media: reference the current output media object.</td>
110</tr>
111</tbody>
112</table>
113
114<h2>Event usage</h2>
115<p>
116A nice sample of events usage was contributed by <b>marco_snake</b> on tufat html2ps/pdf community forum. In this sample,
117events are used to display specific HTML code only on pages with predefined numbers.
118PHP and HTML code is available in <tt>samples/API/events/1</tt> directory in the distribution package.
119</p>
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