Multiple Custom_Background, is it possible?

2 comments

1. Hi @Amit:

   The answer is “Yes, it is possible.” The follow up question is “Do you really want to?”

   I thought it would be fun to see if I could build a plugin to do what you are asking for so I decided to see if it was possible. Of course I was able to make it work but I fear that the plugin code I wrote needs to be so tightly coupled with the existing code in WordPress that it might easily break on a core update.

   This code handles all the admin console side of things by creating a new menu item in the Appearance section called “Special Background.” What it does not do is provide any way to actually use the background; that’s phase two of the plugin and will require hooking many of the functions in /wp-includes/themes.php and frankly I don’t know if I’ll get a chance to write that code.

   The reason I stopped without doing it is I didn’t know the requirements for where the special background should show and where the regular one would show. I assume maybe for selected pages and/or URL paths?

   Nonetheless, here if the code for the plugin (which you can also download from gist):

   <?php
   /*
   Plugin Name: Special Background
   Plugin URI: http://wordpress.stackexchange.com/questions/972/
   Description: Example to show how to add a special background using exiting background admin page in core.
   Version: 0.1
   Author: Mike Schinkel
   Author URI: http://mikeschinkel.com/custom-wordpress-plugins/
   */
   add_filter('admin_menu','add_special_background_menu_item');
   function add_special_background_menu_item() {
       add_theme_page(__('Special Background'), __('Special Background'),'edit_theme_options','special-background','special_background_admin_page');
   }
   add_filter('admin_init','add_js_for_special_background');
   function add_js_for_special_background() {
       global $custom_background;
       if (is_special_background_page()) {
           wp_enqueue_script('custom-background');
           wp_enqueue_style('farbtastic');
       }
       $hook = 'load-appearance_page_special-background';
       add_action($hook, array(&$custom_background, 'admin_load'));
       add_action($hook, array(&$custom_background, 'take_action'), 49);
       add_action($hook, array(&$custom_background, 'handle_upload'), 49);    
   }
   add_filter('theme_mod_background_image',      'theme_mod_special_background_image');
   add_filter('theme_mod_background_image_thumb','theme_mod_special_background_image_thumb');
   add_filter('theme_mod_background_repeat',     'theme_mod_special_background_repeat');
   add_filter('theme_mod_background_position_x', 'theme_mod_special_background_position_x');
   add_filter('theme_mod_background_attachment', 'theme_mod_special_background_attachment');
   add_filter('theme_mod_background_color',      'theme_mod_special_background_color');
   function theme_mod_special_background_image($defaults) {
       return theme_mod_special_background_image_attrs('image',$defaults);
   }
   function theme_mod_special_background_image_thumb($defaults) {
       return theme_mod_special_background_image_attrs('image_thumb',$defaults);
   }
   function theme_mod_special_background_repeat($defaults) {
       return theme_mod_special_background_image_attrs('repeat',$defaults);
   }
   function theme_mod_special_background_position_x($defaults) {
       return theme_mod_special_background_image_attrs('position_x',$defaults);
   }
   function theme_mod_special_background_attachment($defaults) {
       return theme_mod_special_background_image_attrs('attachment',$defaults);
   }
   function theme_mod_special_background_color($defaults) {
       return theme_mod_special_background_image_attrs('color',$defaults);
   }
   function theme_mod_special_background_image_attrs($attr,$defaults) {
       if (is_special_background_page()) {
           $mods = get_option( 'mods_' . get_current_theme() );
           $defaults = (!empty($mods["special_background_{$attr}"]) ? $mods["special_background_{$attr}"] : '');
       }
       return $defaults;
   }
   add_filter('pre_update_option_mods_' . get_current_theme(),'pre_update_option_special_background_image',10,2);
   function pre_update_option_special_background_image($newvalue, $oldvalue) {
       static $times_called = 0;
       if (!empty($_POST) && is_special_background_page()) {
           if ((isset($_POST['action']) && $_POST['action']=='save') || isset($_POST['reset-background']) || isset($_POST['remove-background'])) {
               switch ($times_called) {
                   case 0:
                       $newvalue = special_background_image_value_swap('image',$newvalue,$oldvalue);
                       break;
                   case 1:
                       $newvalue = special_background_image_value_swap('image_thumb',$newvalue,$oldvalue);
                       break;
               }
           } else {
               if ($times_called==0 && isset($_POST['background-repeat'])) {
                   $newvalue = special_background_image_value_swap('repeat',$newvalue,$oldvalue);
               }
               if ($times_called==1 && isset($_POST['background-position-x'])) {
                   $newvalue = special_background_image_value_swap('position_x',$newvalue,$oldvalue);
               }
               if ($times_called==2 && isset($_POST['background-attachment'])) {
                   $newvalue = special_background_image_value_swap('attachment',$newvalue,$oldvalue);
               }
               if ($times_called==3 && isset($_POST['background-color'])) {
               $newvalue = special_background_image_value_swap('color',$newvalue,$oldvalue);
         }
       }
       $times_called++;
     }
     return $newvalue;
   }
   function special_background_image_value_swap($swap_what,$newvalue,$oldvalue) {
     $newvalue["special_background_{$swap_what}"] = $newvalue["background_{$swap_what}"];
     $newvalue["background_{$swap_what}"] = $oldvalue["background_{$swap_what}"];
     return $newvalue;
   }
   function special_background_admin_page() {
     global $custom_background;
     if (is_special_background_page()) {
       global $parent_file,$submenu_file,$title;
       $parent_file = 'themes.php';
       $submenu_file = 'themes.php?page=special-background';
       $title = 'Special Background';
       require_once(ABSPATH . 'wp-admin/admin-header.php');
       ob_start();
       $custom_background->admin_page();
       $html = ob_get_clean();
       $html = preg_replace('#<h2>([^<]+)</h2>#','<h2>Special Background</h2>',$html);
       echo $html;
       include(ABSPATH . 'wp-admin/admin-footer.php');
       exit;
     }
   }
   function is_special_background_page() {
     global $pagenow;
     return ($pagenow=='themes.php' &&
            isset($_GET['page']) && $_GET['page']== 'special-background');
   }
   

   Frankly it is too much code to explain proactively but I’ll be happy to answer specific questions.

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2. Technically it’s possible (so to extend the wordpress source), but not by default. So I would give the answer to no. The build-in background theme feature is for a single graphics only be default.

   But if you describe a little bit more about the “2 different areas” you’re writing about, there might be something nice to suggest next to this.

   Edit: Highlight for MikeSchinkel. Plugins are extending the wordpress source.

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