Converting a simple plugin to be placed inside of functions.php

First off, I know it’s better practice to use plugins separately than to integrate them in functions.php but this is for a theme framework that will be deployed to multiple sites and it will be easier to have it packaged as part of the theme.

I am having trouble using the following code from the plugin located here. My PHP knowledge is limited, I have tried copying and pasting the code directly but it does not work, but works fine when used as a plugin.

class Filosofo_Custom_Image_Sizes {

public function __construct()
{
    add_filter('image_downsize', array(&$this, 'filter_image_downsize'), 99, 3);

}

/**
 * Callback for the "image_downsize" filter.
 *
 * @param bool $ignore A value meant to discard unfiltered info returned from this filter.
 * @param int $attachment_id The ID of the attachment for which we want a certain size.
 * @param string $size_name The name of the size desired.
 */
public function filter_image_downsize($ignore = false, $attachment_id = 0, $size_name = 'thumbnail')
{
    global $_wp_additional_image_sizes;

    $attachment_id = (int) $attachment_id;
    $size_name = trim($size_name);

    $meta = wp_get_attachment_metadata($attachment_id);

    /* the requested size does not yet exist for this attachment */
    if (
        empty( $meta['sizes'] ) ||
        empty( $meta['sizes'][$size_name] )
    ) {
        // let's first see if this is a registered size
        if ( isset( $_wp_additional_image_sizes[$size_name] ) ) {
            $height = (int) $_wp_additional_image_sizes[$size_name]['height'];
            $width = (int) $_wp_additional_image_sizes[$size_name]['width'];
            $crop = (bool) $_wp_additional_image_sizes[$size_name]['crop'];

        // if not, see if name is of form [width]x[height] and use that to crop
        } else if ( preg_match('#^(d+)x(d+)$#', $size_name, $matches) ) {
            $height = (int) $matches[2];
            $width = (int) $matches[1];
            $crop = true;
        }

        if ( ! empty( $height ) && ! empty( $width ) ) {
            $resized_path = $this->_generate_attachment($attachment_id, $width, $height, $crop);
            $fullsize_url = wp_get_attachment_url($attachment_id);

            $file_name = basename($resized_path);

            $new_url = str_replace(basename($fullsize_url), $file_name, $fullsize_url);

            if ( ! empty( $resized_path ) ) {
                $meta['sizes'][$size_name] = array(
                    'file' => $file_name,
                    'width' => $width,
                    'height' => $height,
                );

                wp_update_attachment_metadata($attachment_id, $meta);

                return array(
                    $new_url,
                    $width,
                    $height,
                    true
                );
            }
        }
    }

    return false;
}

/**
 * Creates a cropped version of an image for a given attachment ID.
 *
 * @param int $attachment_id The attachment for which to generate a cropped image.
 * @param int $width The width of the cropped image in pixels.
 * @param int $height The height of the cropped image in pixels.
 * @param bool $crop Whether to crop the generated image.
 * @return string The full path to the cropped image.  Empty if failed.
 */
private function _generate_attachment($attachment_id = 0, $width = 0, $height = 0, $crop = true)
{
    $attachment_id = (int) $attachment_id;
    $width = (int) $width;
    $height = (int) $height;
    $crop = (bool) $crop;

    $original_path = get_attached_file($attachment_id);

    // fix a WP bug up to 2.9.2
    if ( ! function_exists('wp_load_image') ) {
        require_once ABSPATH . 'wp-admin/includes/image.php';
    }

    $resized_path = @image_resize($original_path, $width, $height, $crop);

    if ( 
        ! is_wp_error($resized_path) && 
        ! is_array($resized_path)
    ) {
        return $resized_path;

    // perhaps this image already exists.  If so, return it.
    } else {
        $orig_info = pathinfo($original_path);
        $suffix = "{$width}x{$height}";
        $dir = $orig_info['dirname'];
        $ext = $orig_info['extension'];
        $name = basename($original_path, ".{$ext}"); 
        $destfilename = "{$dir}/{$name}-{$suffix}.{$ext}";
        if ( file_exists( $destfilename ) ) {
            return $destfilename;
        }
    }

    return '';
}
}

function initialize_custom_image_sizes()
{
new Filosofo_Custom_Image_Sizes;
}

add_action('plugins_loaded', 'initialize_custom_image_sizes');

I’m aware I can achieve the same results using TimThumb but I would much prefer to use the built in functionality of WordPress

Here’s a link to the plugin in question:-

http://wordpress.org/extend/plugins/custom-image-sizes/

Thanks in advance!

Steve