function add_meta(){
  global $template, $page, $meta_infos;
  $meta_infos = array();
  $meta_infos['author'] = $template->get_template_vars('INFO_AUTHOR');
  $meta_infos['related_tags'] = $template->get_template_vars('related_tags');
  $meta_infos['info'] = $template->get_template_vars('INFO_FILE');
  $meta_infos['title'] = $template->get_template_vars('PAGE_TITLE');
//ADDED BY PHOTONOXX
  $meta_infos['desc'] = $template->get_template_vars('CONTENT_DESCRIPTION');

  $query = 'SELECT id,metaname,metaval FROM ' . meta_TABLE . ' WHERE metaname IN (\'author\', \'keywords\', \'Description\', \'robots\');';
  $result = pwg_query($query);
  $meta = array();
  while ($row = pwg_db_fetch_assoc($result)){
    $meta[$row['metaname']] = $row['metaval'];
    $metaED[$row['metaname']] = trigger_change('AP_render_content', $meta[$row['metaname']]);
  }

  // Authors
  if (!empty($meta_infos['author']) and ! empty($metaED['author'])){
    $template->assign('INFO_AUTHOR', $meta_infos['author'] . ' - ' . $metaED['author']);
  } elseif (!empty($metaED['author'])){
    $template->assign('INFO_AUTHOR', $metaED['author']);
  }

  // Keywords
  if (!empty($metaED['keywords'])){
    $template->append('related_tags', array('name' => $metaED['keywords']));
  }

  // Description

//MODIFIED BY PHOTONOXX ajout d'une étape elseif et du champ $meta_info['desc'] dans les deux premiers if elseif

  if (!empty($meta_infos['title']) and !empty($meta_infos['desc']) and ! empty($meta_infos['info']) and ! empty($metaED['Description'])) {
    $template->assign('PLUG_META', $meta_infos['title'] . ' - ' . $meta_infos['desc'] . ' - ' .$meta_infos['info'] . ', ' . $metaED['Description']);
  } elseif (!empty($meta_infos['title']) and !empty($meta_infos['desc']) and ! empty($metaED['Description'])) {
    $template->assign('PLUG_META', $meta_infos['title'] . ' - ' . $meta_infos['desc'] . ' - ' . $metaED['Description']);
  } elseif (!empty($meta_infos['title']) and ! empty($metaED['Description'])) {
    $template->assign('PLUG_META', $meta_infos['title'] . ' - ' . $metaED['Description']);
  } elseif (!empty($metaED['Description'])) {
    $template->assign('PLUG_META', $metaED['Description']);
  }

  // Robots
  if (!empty($meta['robots'])) {
    $template->append('head_elements', '<meta name="robots" content="' . $meta['robots'] . '">');
  }

  //Metaperso
  if (script_basename() !== 'admin') {
    $metapersos = pwg_query("SELECT * FROM " . METAPERSO_TABLE . ";");

    if (pwg_db_num_rows($metapersos)) {
      while ($metaperso = pwg_db_fetch_assoc($metapersos)) {
        $items = array(
          'METANAME' => $metaperso['metaname'],
          'METAVAL' => $metaperso['metaval'],
          'METATYPE' => $metaperso['metatype']
        );
        $template->append('metapersos', $items);
      }
    }

    $template->set_filename('PERSO_META', realpath(meta_PATH . 'persometa.tpl'));
    $template->append('head_elements', $template->parse('PERSO_META', true));
  }

  $MPC = pwg_db_fetch_assoc(pwg_query("SELECT state FROM " . PLUGINS_TABLE . " WHERE id = 'ContactForm';"));
  if ($MPC['state'] == 'active'){
    global $conf;
    if (isset($page['section']) and $page['section'] == 'contact' and isset($conf['contactmeta']) and strpos($conf['contactmeta'], ',') !== false){
      $metacontact = explode(',', $conf['contactmeta']);
      $metakeyED = trigger_change('AP_render_content', $metacontact[0]);
      $metadesED = trigger_change('AP_render_content', $metacontact[1]);
      if (!empty($metakeyED)){
        $template->append('related_tags', array('name' => $metakeyED));
      }
      if (!empty($metadesED)){
        $template->assign('PLUG_META', $metadesED);
      }
    }
  }

  $MAP = pwg_db_fetch_assoc(pwg_query("SELECT state FROM " . PLUGINS_TABLE . " WHERE id = 'AdditionalPages';"));
  if ($MAP['state'] == 'active') {
    if (!empty($page['additional_page']['id'])) {
      $lire = $page['additional_page']['id'];
      $query = 'SELECT id, metaKeyap, metadesap FROM ' . META_AP_TABLE . ' WHERE id = \'' . $lire . '\';';
    $result = pwg_query($query);
    $row = pwg_db_fetch_assoc($result);
    $metaKeyapap = $row['metaKeyap'];
    $metadesapap = $row['metadesap'];
    $metaKeyapapED = trigger_change('AP_render_content', $metaKeyapap);
    $metadesapED = trigger_change('AP_render_content', $metadesapap);
    }
  if (isset($page['section']) and $page['section'] == 'additional_page') {
    if (!empty($metaKeyapapED)) {
    $template->append('related_tags', array('name' => $metaKeyapapED));
    }
    if (!empty($metadesapED)) {
    $template->assign('PLUG_META', $metadesapED);
    }
  }
  }
}

function upmata($content, &$smarty){
  $search = '#<meta name="description" content=".*?">#';
  $replacement = '<meta name="description" content="{$PLUG_META}">';
  return preg_replace($search, $replacement, $content);
}

<!DOCTYPE html>
<html lang="{$lang_info.code}" dir="{$lang_info.direction}">
<head>
    <meta http-equiv="Content-Type" content="text/html; charset={$CONTENT_ENCODING}">
    <meta name="generator" content="Piwigo (aka PWG), see piwigo.org">
    <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0">
    <meta name="mobile-web-app-capable" content="yes">
    <meta name="apple-mobile-web-app-capable" content="yes">
    <meta name="apple-mobile-web-app-status-bar-style" content="black-translucent">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
{if $meta_ref_enabled}
{if isset($INFO_AUTHOR)}
    <meta name="author" content="{$INFO_AUTHOR|@strip_tags:false|@replace:'"':' '}">
{/if}
{if isset($related_tags)}
    <meta name="keywords" content="{foreach from=$related_tags item=tag name=tag_loop}{if !$smarty.foreach.tag_loop.first}, {/if}{$tag.name}{/foreach}">
{/if}
{if isset($COMMENT_IMG)}
    <meta name="description" content="{$COMMENT_IMG|@strip_tags:false|@replace:'"':' '}{if isset($INFO_FILE)} - {$INFO_FILE}{/if}">
{else}
    <meta name="description" content="{$PAGE_TITLE}{if !empty($CONTENT_DESCRIPTION)} - {$CONTENT_DESCRIPTION}{/if}{if isset($INFO_FILE)} - {$INFO_FILE}{/if}">
{/if}
{/if}

<meta name="description" content="{$PAGE_TITLE}{if isset($INFO_FILE)} - {$INFO_FILE}{/if}">