$smarty->register_function('sprite', 'smarty_function_sprite');

  // get PATH_INFO

  $pathinfo = @substr(@substr($_SERVER['REQUEST_URI'], 1), @strpos(@substr($_SERVER['REQUEST_URI'], 1), '/')+1);

  // should we do a collage (for CSS sprites instead of sending hundreds of individual images)?

  if ( preg_match('/^collage(?:\/([0-9]+))?$/', $pathinfo, $match) )

  {

    // default size is 50px per image

    $collage_size = ( isset($match[1]) ) ? intval($match[1]) : 50;

    $artwork_dir = "$amarok_home/albumcovers";

    if ( !file_exists("$artwork_dir/collage_{$collage_size}.png") )

    {

      if ( !generate_artwork_collage("$artwork_dir/collage_{$collage_size}.png", $collage_size) )

      {

        echo 'Error: generate_artwork_collage() failed';

        return;

      }

    }

    $target_file = "$artwork_dir/collage_{$collage_size}.png";

    // we have it now, send the image through

    $fh = @fopen($target_file, 'r');

    if ( !$fh )

      return false;

    $httpd->header('Content-type: image/png');

    $httpd->header('Content-length: ' . filesize($target_file));

    $httpd->header('Expires: Wed, 1 Jan 2020 01:00:00 GMT');

    // kinda sorta a hack.

    $headers = implode("\r\n", $httpd->response_headers);

    $httpd->send_client_headers($socket, $httpd->response_code, $httpd->content_type, $headers);

    while ( $d = fread($fh, 10240) )

    {

      $socket->write($d);

    }

    fclose($fh);

    return;

  }

        // image is not supported (PNG, GIF, or JPG required)

    // kinda sorta a hack.

    $headers = implode("\r\n", $httpd->response_headers);

    $httpd->send_client_headers($socket, $httpd->response_code, $httpd->content_type, $headers);

      $socket->write(fread($fh, 51200));

/**

 * Generates a collage of all album art for use as a CSS sprite. Also generates a textual .map file in the format of "hash xpos ypos\n"

 * to allow retrieving positions of images. Requires GD.

 * @param string Name of the collage file. Map file will be the same filename except with the extension ".map"

 * @param int Size of each image, in pixels. Artwork images will be stretched to a 1:1 aspect ratio. Optional, defaults to 50.

 * @return bool True on success, false on failure.

 */

function generate_artwork_collage($target_file, $size = 50)

{

  // check for required GD functionality

  if ( !function_exists('imagecopyresampled') || !function_exists('imagepng') )

    return false;

  status("generating size $size collage");

  $stderr = fopen('php://stderr', 'w');

  if ( !$stderr )

    // this should really never fail.

    return false;

  // import amarok globals

  global $amarok_home;

  $artwork_dir = "$amarok_home/albumcovers";

  // map file path

  $mapfile = preg_replace('/\.[a-z]+$/', '', $target_file) . '.map';

  // open map file

  $maphandle = @fopen($mapfile, 'w');

  if ( !$maphandle )

    return false;

  $mapheader = <<<EOF

# this artwork collage map gives the locations of various artwork images within the collage

# format is:

# hash                           x y

# x and y are indices, not pixel values (obviously), and hash is the name of the artwork file in large/

EOF;

  fwrite($maphandle, $mapheader);

  // build a list of existing artwork files

  $artwork_list = array();

  if ( $dh = @opendir("$artwork_dir/large") )

  {

    while ( $fp = @readdir($dh) )

    {

      if ( preg_match('/^[a-f0-9]{32}$/', $fp) )

      {

        $artwork_list[] = $fp;

      }

    }

    closedir($dh);

  }

  else

  {

    return false;

  }

  // at least one image?

  if ( empty($artwork_list) )

    return false;

  // asort it to make sure map is predictable

  asort($artwork_list);

  // number of columns

  $cols = 20;

  // number of rows

  $rows = ceil( count($artwork_list) / $cols );

  // image dimensions

  $image_width  = $cols * $size;

  $image_height = $rows * $size;

  // create image

  $collage = imagecreatetruecolor($image_width, $image_height);

  // generator loop

  // start at row 0, column 0

  $col = -1;

  $row = 0;

  $srow = $row + 1;

  fwrite($stderr, "  -> row $srow of $rows\r");

  $time_map = microtime(true);

  foreach ( $artwork_list as $artwork_file )

  {

    // calculate where we are

    $col++;

    if ( $col == $cols )

    {

      // reached column limit, reset $cols and increment row

      $col = 0;

      $row++;

      $srow = $row + 1;

      fwrite($stderr, "  -> row $srow of $rows\r");

    }

    // x and y offset of scaled image

    $xoff = $col * $size;

    $yoff = $row * $size;

    // set offset

    fwrite($maphandle, "$artwork_file $col $row\n");

    // load image

    $createfunc = ( get_image_filetype("$artwork_dir/large/$artwork_file") == 'jpg' ) ? 'imagecreatefromjpeg' : 'imagecreatefrompng';

    $aw = @$createfunc("$artwork_dir/large/$artwork_file");

    if ( !$aw )

    {

      $aw = @imagecreatefromwbmp("$artwork_dir/large/$artwork_file");

      if ( !$aw )

      {

        // couldn't load image, silently continue

        continue;

      }

    }

    list($aw_width, $aw_height) = array(imagesx($aw), imagesy($aw));

    // scale and position image

    $result = imagecopyresampled($collage, $aw, $xoff, $yoff, 0, 0, $size, $size, $aw_width, $aw_height);

    if ( !$result )

    {

      // couldn't scale image, silently continue

      continue;

    }

    // free the temp image

    imagedestroy($aw);

  }

  $time_map = round(1000 * (microtime(true) - $time_map));

  $time_write = microtime(true);

  fclose($maphandle);

  fwrite($stderr, "  -> saving image\r");

  if ( !imagepng($collage, $target_file) )

    return false;

  imagedestroy($collage);

  $time_write = round(1000 * (microtime(true) - $time_write));

  $avg = round($time_map / count($artwork_list));

  status("collage generation complete, returning success; time (ms): map/avg/write $time_map/$avg/$time_write");

  return true;

}

/**

 * Returns an img tag showing artwork from the specified size collage sprite.

 * @param string Artist

 * @param string Album

 * @param int Collage size

 * @return string

 */

function get_artwork_sprite($artist, $album, $size = 50)

{

  // import amarok globals

  global $amarok_home;

  $artwork_dir = "$amarok_home/albumcovers";

  if ( !is_int($size) )

    return '';

  // hash of cover

  $coverid = md5(strtolower(trim($artist)) . strtolower(trim($album)));

  $tag = '<img alt=" " src="/spacer.gif" width="' . $size . '" height="' . $size . '" ';

  if ( file_exists("$artwork_dir/collage_{$size}.map") )

  {

    $mapdata = parse_collage_map("$artwork_dir/collage_{$size}.map");

    if ( isset($mapdata[$coverid]) )

    {

      $css_x = -1 * $size * $mapdata[$coverid][0];

      $css_y = -1 * $size * $mapdata[$coverid][1];

      $tag .= "style=\"background-image: url(/artwork/collage/$size); background-repeat: no-repeat; background-position: {$css_x}px {$css_y}px;\" ";

    }

  }

  $tag .= '/>';

  return $tag;

}

/**

 * Parses the specified artwork map file. Return an associative array, keys being the artwork file hashes and values being array(x, y).

 * @param string Map file

 * @return array

 */

function parse_collage_map($mapfile)

{

  if ( !file_exists($mapfile) )

    return array();

  $fp = @fopen($mapfile, 'r');

  if ( !$fp )

    return false;

  $map = array();

  while ( $line = fgets($fp) )

  {

    // parse out comments

    $line = trim(preg_replace('/#(.+)$/', '', $line));

    if ( empty($line) )

      continue;

    list($hash, $x, $y) = explode(' ', $line);

    if ( !preg_match('/^[a-f0-9]{32}$/', $hash) || !preg_match('/^[0-9]+$/', $x) || !preg_match('/^[0-9]+$/', $y) )

      // invalid line

      continue;

    // valid line, append map array

    $map[$hash] = array(

        intval($x),

        intval($y)

      );

  }

  fclose($fp);

  return $map;

}

/**

 * Finds out if a collage file is outdated (e.g. missing artwork images)

 * @param int Size of collage

 * @return bool true if outdated

 */

function collage_is_outdated($size = 50)

{

  global $amarok_home;

  $artwork_dir = "$amarok_home/albumcovers";

  $mapfile = "$artwork_dir/collage_{$size}.map";

  if ( !file_exists($mapfile) )

  {

    // consider it outdated if it doesn't exist

    return true;

  }

  // load existing image map

  $map = parse_collage_map($mapfile);

  // build a list of existing artwork files

  $artwork_list = array();

  if ( $dh = @opendir("$artwork_dir/large") )

  {

    while ( $fp = @readdir($dh) )

    {

      if ( preg_match('/^[a-f0-9]{32}$/', $fp) )

      {

        // found an artwork file

        if ( !isset($map[$fp]) )

        {

          // this artwork isn't in the map file, return outdated

          closedir($dh);

          status("size $size collage is outdated");

          return true;

        }

      }

    }

    closedir($dh);

  }

  // if we reach here, we haven't found anything missing.

  return false;

}

/**

 * Smarty function for sprite generation.

 * @access private

 */

function smarty_function_sprite($params, &$smarty)

{

  // don't perform the exhaustive check more than once per execution

  static $checks_done = array();

  if ( empty($params['artist']) )

    return 'Error: missing "artist" parameter';

  if ( empty($params['album']) )

    return 'Error: missing "album" parameter';

  if ( empty($params['size']) )

    $params['size'] = 50;

  $params['size'] = intval($params['size']);

  $size =& $params['size'];

  // if the collage file doesn't exist or is missing artwork, renew it

  // but only perform this check once per execution per size

  if ( !isset($checks_done[$size]) )

  {

    global $amarok_home;

    $artwork_dir = "$amarok_home/albumcovers";

    $collage_file = "$artwork_dir/collage_{$size}";

    $collage_is_good = file_exists("$collage_file.png") && file_exists("$collage_file.map") && !collage_is_outdated($size);

    if ( !$collage_is_good )

    {

      generate_artwork_collage("$collage_file.png", $size);

    }

    $checks_done[$size] = true;

  }

  return get_artwork_sprite($params['artist'], $params['album'], $params['size']);

}