Drupal | Omega | Transform the main menu into a select to be used into small screen sizes.

drupal-template.php

// see also https://gist.github.com/3201854

function mytheme_menu_tree__main_menu($variables) {	
	return '<select class="mobile-main-menu" onchange="location = this.options[this.selectedIndex].value;">'
			 . $variables['tree'] . '</select>';
}

function mytheme_menu_link__main_menu($variables) {
	global $base_url;
	$e = $variables['element'];
	
	$attr = "";
	if (isset($e['#localized_options']['attributes']['class'][0])
			&& $e['#localized_options']['attributes']['class'][0] == "active-trail")
		$attr = 'selected="selected"';
	
	$link = $e['#href'] == "<front>" ? $base_url : $base_url . "/" . $e['#href'];
	return '<option value="' . $link . '" ' . $attr . '>' .  $e['#title'] . "</option>";
}


//main menu (level 2 sidebar) using the menu block module
function mytheme_menu_tree__menu_block__1(&$variables) {
	return '<ul class="sidebar-menu">' . $variables['tree'] . '</ul>';
}

function mytheme_menu_link__menu_block__1($variables) {
	$element = $variables['element'];
	$sub_menu = '';

	if ($element['#below']) {
		$sub_menu = drupal_render($element['#below']);
	}
	$output = l($element['#title'], $element['#href'], $element['#localized_options']);
	return '<li' . drupal_attributes($element['#attributes']) . '>' . $output . $sub_menu . "</li>\n";
}