Plugin developpement

Plugins are designed to extend the Piwigo features.

You will find in the Skeleton a good bootstrap for you plugin.

Plugin architecture

A plugin can hook into the core of Piwigo by registering event handlers with Piwigo. An event handler is nothing more than a function that Piwigo will call.

register_event_handler('delete_user', 'my_action_on_delete_user');

In this case, 'delete_user' is the name of the event to which the plugin will hook. Piwigo will automatically call your function when a user is deleted.

Piwigo will trigger notices and changes. The only difference from a coding perspective is that you are required to return a value in the case of an event (this return value will be used later by Piwigo).

An example of trigger_notify is 'delete_user' or 'delete_elements'. Your plugin can take any required actions when a user is deleted by registering an event handler for 'delete_user'. While handling actions you are not expected to directly return a value that will be used by Piwigo, but you can modify any global variable in order to change the general behaviour.

An example of trigger_change is 'render_user_comment_content'. Piwigo will give in input the raw content of a comment, you can modify it at your will (for example allow bbcode or add smilies) and return the value:

register_event_handler('render_user_comment_content', 'my_function');
function my_function($content)
  $content = str_replace(':)', '<img src="" alt=":)" />', $content);
  return $content; //<-- NOTE: this is how you return the value to Piwigo 

A complete reference of core triggers is available at tools/triggers_list.php into your Piwigo installation, or here (not always up to date).

Taxonomy of a plugin

The minimal plugin is a file called (in the directory plugins/my_plugin if your plugin is called my_plugin). It MUST have the header below:

<?php /*
Version: 1.0
Plugin Name: Short Name (shown on the plugins management page)
Plugin URI:
Author: My Name
Author URI:
Description: This a little bit longer description is also shown on the plugins management page

Note that the version number is saved into database, so keep it short and in a good style ( 1.1 or 1.a.b …)


While nobody will impose a coding standard here are some things you should consider:

Name collisions

PHP does not allow several function names to be defined at the same time. Keep in mind that your plugin will need to work with other plugins activated, as well as the core of Piwigo, so please avoid function names such as 'send', 'delete', 'delete_user'… You have two options:

A. Prefix function names with something unique: 'download_multi_delete_user', 'download_multi_delete_elements', etc…

B. Use objects and classes

// static EXAMPLE
class MyClass
  function on_delete_user() { ... }
add_event_handler('delete_user', array('MyClass', 'on_delete_user'));
// object EXAMPLE
class MyClass
  function on_delete_user() { ... }
$myObj = new MyClass();
add_event_handler('delete_user', array(&$myObj, 'on_delete_user') );

Extensions compatibility

If your plugin adds or load custom tpl, to the public part, you should let to the theme the ability to define their own tpl file. If your plugin defines a new index page, like index.php?/xxxx, $page['title'], $page['body_id'] and $page['section'] needs to be defined with custom values by the plugin, using the loc_end_section_init trigger. This is useful for other plugins and themes, in order to declare what type of page is currently running.

Code size

When Piwigo loads the plugins, it will include every Don't put in your 3000 lines of code just to add a page on the administration menu. Split you in several files and feel free to add include_once inside functions defined in as much as you want.

Also use the lazy loading feature of add_event_handler (Piwigo 2.7 and above)

// without lazy loading, necessary code is loaded immediately
include_once(SKELETON_PATH . 'include/');
add_event_handler('rare_trigger', 'my_function');
// with lazy loading, code loaded only id needed
add_event_handler('rare_trigger', 'my_function', 50,
  SKELETON_PATH . 'include/');

Do not 'die()'

If you call functions such as die or exit within your plugin, keep in mind that the final user will have no other choice than modify his config file so that no plugin is loaded or modify the #plugins table (if he knows that the cause is your plugin). So please whenever something is wrong, the plugins should display a message for the administrators and silently do nothing.

What can be done when is executed ?

Piwigo will include at some point during the initialization. At this time, do not make any assumption that the user is logged in, the language is defined, the template is created, etc. The only safe assumptions are:

  • the connection to the database has been established
  • the configuration has been loaded
  • you can safely call add_event_handler, remove_event_handler. For all other cases, you must hook the event 'init'. The 'init' event is triggered only once and at that point the common initialization of the current page is finished

Plugin maintenance

When a plugin is installed, activated, deactivated or uninstalled, Piwigo will allow you to take some special steps by executing some php code. If you have a php file named or maintain.class.php in your plugin directory, Piwigo will include this file and will call some maintenance functions.

Piwigo 2.7 and above

Maintenance functions have to be declared in maintain.class.php by class extending PluginMaintain :

 * PLUGINID must be replaced by the directory name of your plugin
class PLUGINID_maintain extends PluginMaintain
  function install($plugin_version, &$errors=array()) { ... }
  function activate($plugin_version, &$errors=array()) { ... }
  function update($old_version, $new_version, &$errors=array()) { ... }
  function deactivate() { ... }
  function uninstall() { ... }

Piwigo 2.6 and bellow

Maintenance functions are declared in and are all optional :

function plugin_install($plugin_id, $plugin_version, &$errors) { ... }
function plugin_activate($plugin_id, $plugin_version, &$errors) { ... }
function plugin_deactivate($plugin_id) { ... }
function plugin_uninstall($plugin_id) { ... }
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dev/extensions/plugins.txt · Last modified: 2019/08/15 07:53 by executive
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