special-background.php

<?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;
}
//add_action('load-appearance_page_custom-background','load_appearance_page_custom_background');
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';
		$title = 'Special Background';
		//if (empty($_POST)) {
			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');
}