Get the Bounding Box of an SVG Path

<?php
 
/**
 * Determines the bounding box of a specific path, rectangle, polygon, or ellipses
 * in an SVG.  Accepts the SVG's DOM, and the node specifically desired to be checked.
 * Assumes convert is at /usr/bin/convert unless a global called $convertpath is set.
 *
 * @param DOMDocument $svg SVG DOMDocument to use to find this item's bounding box.
 * @param DOMDocument $object Node that we want to find the bounding box for.
 * @param Float $precision Precision desired, 1 is rougly pixel-accurate, between 0.1 and 1 is less than pixel accurate
 *   and anything above 1 should be sub-pixel accurate.  (Max is 3)
 * @return Mixed Boolean false on failure, Array with topleft-x, topleft-y, bottomright-x, bottomright-y in percentages
 */
function discover_bounding_box($svg, $object, $precision = 1)
{
   global $convertpath;
   $convert = isset($convertpath) ? $convertpath : '/usr/bin/convert';
   // We assume density 72 is the pixel-size accurate 
   $density = 72;
   if($precision >= 0.1 && $precision <= 3)
   {
       $density = floor(72*$precision);
   }
 
   $singlesvg = create_single_object_svg($svg, $object);
 
 
   //Now that we've got the SVG in hand, let's pass it on to process image.
   ob_start();
   process_image($singlesvg, '-trim', 'svg', 'info', "-density $density");
   $info = trim(ob_get_clean());
 
   //Tokenize the fragments of text from our friend, ImageMagick.
   $fragments = explode(' ', $info);
 
   list($trimmed_width, $trimmed_height) = explode('x', $fragments[2]);
   //If both intval'd are not 0, then we can assume that all when well.
   if( ($trimmed_width = intval($trimmed_width)) > 0 && ($trimmed_height = intval($trimmed_height)) > 0)
   {
      //Now get the original width, original height, clip offsetx and clip offsety
      list($original_width, $original_height, $clip_offsetx, $clip_offsety) = 
         array_map('_intval', explode('+', str_replace('x', '+', $fragments[3])));
 
      $bounding_top_left_x = $clip_offsetx/$original_width;
      $bounding_top_left_y = $clip_offsety/$original_height;
      $bounding_bottom_right_x = ($clip_offsetx+$trimmed_width)/$original_width;
      $bounding_bottom_right_y = ($clip_offsety+$trimmed_height)/$original_height;
 
      return array($bounding_top_left_x, $bounding_top_left_y, 
         $bounding_bottom_right_x, $bounding_bottom_right_y);
   }
 
   return false;
}
 
 
/**
 * Creates an extract from an SVG based on an input DOM and desired object.
 * @param DOMDocument $svg A fully loaded DOMDocument for the SVG.
 * @param DOMNode $object Target node to extract.
 * @return String Returns an SVG file containing only the desired object.  At present
 * this function also removes patterns and gradients which may be a notable problem in 
 * cases where you want to find the visible bounding box of an object, not necessarily
 * it's exact box.
 */
function create_single_object_svg($svg, $object)
{
   //Get the width and height of the current document.
   $root = $svg->getElementsByTagName('svg')->item(0);
   $width = htmlspecialchars($root->getAttribute('width'));
   $height = htmlspecialchars($root->getAttribute('height'));
 
   //It's best if you have a solid color set in the style or fill attribute
   //but it shouldn't be that big a deal.   
 
   //Get an transforms from group nodes.
   $transforms = array();
   $current = $object;
   while($current->parentNode) //Continue climbing until there's no where else to climb to.
   {
      $current = $current->parentNode;
      if($current->nodeName == 'g')
      {
         $transforms[] = $current->getAttribute('transform');
      }
   }
 
 
/**
 * Run stuff through image_magick uses the global convert path settings.  Outputs image on success (and sets header)
 * @param String $imgdata Raw image file data to pipe to image magick.
 * @param String $processing_instruction Command line options to pass to image magick's convert program.
 * @param String $inputtype Default: jpg Input image format.
 * @param String $outputtype Default: jpg Output image format.
 * @param String $preload_instructions Add instructions that go before the file to load.
 * @return void
 */
function process_image($imgdata, $processing_instruction, $inputtype = 'jpg', $outputtype = 'jpg', $preload_instructions = '')
{
   global $convertpath;
 
   if(function_exists('proc_open'))
   {
      //Let's just pipe to imagemagick to handle our graphics transform shall we?
      $descriptors = array(
         '0' => array("pipe", 'r'),
         '1' => array("pipe", 'w'),
         '2' => array("file", "/dev/null", "w")
      );
 
      $pipes = array();
      $process = proc_open($command = "$convertpath $preload_instructions {$inputtype}:- $processing_instruction {$outputtype}:-", $descriptors, $pipes, NULL, NULL, array('binary_pipes' => true));
      //die($command);
      if($process)
      {
         fwrite($pipes[0], $imgdata);
         //fwrite($pipes[0], EOF);
         fclose($pipes[0]);
         $contents = stream_get_contents($pipes[1]);
         proc_close($process);
 
         if(strlen($contents) > 50 || $outputtype == 'info')
         {
            echo $contents;
         }
         else
         {
            header('HTTP/1.1 500 Internal Error');
            header('content-type: text/plain');
            echo 'Failed to process image.';
         }
      }
      else
      {
         //Poor process died.  Should we do something?
         header('HTTP/1.1 500 Internal Error');
         header('content-type: text/plain');
         echo 'Failed to process image.';               
      }
   }
}
 
?>