Rainbow Text

<?
/* Rainbow Text generator v0.1
 *   Gives a different-colored text-shadow to each character in a string to match a rainbow pattern
 *   i.e. Red -> Yellow -> Green -> Cyan -> Fuschia -> Red
 *   Usage: echo rainbowText($longString);
 */

  function rainbowText($input) {
    $l = strlen($input);
    $r = 0;
    $g = 0;
    $b = 0;
    $rg = floor($l / 3);
    $sep = $rg / 2;
    $gb = ceil(2*$l / 3);
    $ret = '';
    for($i = 0; $i < $l; $i++) {
      if($i <= $rg) {
        // First third: Red to green
        if($i >= $sep) {
          $r = floor(255 * (1 - (($i-$sep)/$sep)));
          $g = 255;
        } else {
          $r = 255;
          $g = floor(255 * ($i/$sep));
        }
        $b = 0;
      } elseif($i <= $gb) {
        // Green to blue
        $r = 0;
        if($i >= ($rg + $sep) ) {
          $g = floor(255 * (1 - (($i-($rg + $sep))/($gb-($rg + $sep)))) );
          $b = 255;
        } else {
          $g = 255;
          $b = floor(255 * (1 + (($i-($rg + $sep))/($gb-($rg + $sep)))) );
        }
      } else {
        // Finally: Blue to red
        $g = 0;
        if($i >= ($gb + $sep) ) {
          $b = floor(255 * (1 - (($i-($gb + $sep))/($l-($gb + $sep)))) );
          $r = 255;
        } else {
          $b = 255;
          $r = floor(255 * (1 + (($i-($gb + $sep))/($l-($gb + $sep)))) );
        }
      }
      $ret .= "<span style=\"text-shadow: rgb({$r}, {$g}, {$b}) 0px 1px 1px;\">{$input[$i]}</span><!--\n-->";
    }
    return $ret;
  }
?>

Not sure how useful this will be to anyone else.