SVG bounding box

<?php

/**
 * Calculate smallest bounding rectangle for given SVG path string.
 *
 * Only handles paths composed of straight lines. Bezier and arc commands throw an exception.
 * Returns an object with top left (x1, y1) bottom right (x2, x2) and size (width, height).
 *
 * Example usage:
 *   $bounds = svgBounds('M 100 100L300 100 200 300z');
 *   echo $bounds->width; //200
 *
 * @param string $pathString SVG path command
 * @return stdClass
 * @author Tamlyn Rhodes <http://tamlyn.org>
 * @license http://creativecommons.org/publicdomain/mark/1.0/ Public Domain
 */
function svgBounds($pathString) {
    //match each command sequence starting with a letter
    preg_match_all('/([mlvhz][^mlvhz]*)/i', $pathString, $commands);

    //handle initial move command
    $firstMove = array_shift($commands[0]);
    preg_match_all('/(-?[0-9.]+)/', $firstMove, $matches);
    $pt = $matches[1];
    $bounds = (object) array('x1' => $pt[0], 'y1' => $pt[1], 'x2' => $pt[0], 'y2' => $pt[1]);

    //loop through successive command sequences
    foreach ($commands[0] as $command) {

        //match numbers in string
        preg_match_all('/(-?[0-9.]+)/', $command, $matches);

        //loop through numbers and move point according to command
        $i=0;
        while ($i < count($matches[1])) {

            //update current position
            switch ($command[0]) {
                case 'm' :
                case 'l' :
                    $pt[0] += $matches[1][$i++];
                    $pt[1] += $matches[1][$i++];
                    break;
                case 'M' :
                case 'L' :
                    $pt[0] = $matches[1][$i++];
                    $pt[1] = $matches[1][$i++];
                    break;
                case 'v' :
                    $pt[1] += $matches[1][$i++];
                    break;
                case 'V' :
                    $pt[1] = $matches[1][$i++];
                    break;
                case 'h' :
                    $pt[0] += $matches[1][$i++];
                    break;
                case 'H' :
                    $pt[0] = $matches[1][$i++];
                    break;
                case 'z' :
                case 'Z' :
                    break;
                default :
                    throw new RuntimeException("Unhandled path command: ".$command[0]);
            }

            //expand bounds
            $bounds->x1 = min($bounds->x1, $pt[0]);
            $bounds->y1 = min($bounds->y1, $pt[1]);
            $bounds->x2 = max($bounds->x2, $pt[0]);
            $bounds->y2 = max($bounds->y2, $pt[1]);
        }

    }

    //calculate width and height
    $bounds->width = $bounds->x2 - $bounds->x1;
    $bounds->height = $bounds->y2 - $bounds->y1;

    return $bounds;
}