MODx - MimeTeX Plugin

For the mathematical formula on this site I use the MimeTeX plugin for generating them from Latex style equations. The plugin had several issues. The main one being the fact that the rich text editor included with MODx would strip the invalid <tex> tag. The other being that it doesn't set alt attribute.
The updated code now uses the <pre class="math"> tag and also sets the alt attribute.

/*
mimeTeX Plugin
===================

This plugin lets you easily embed LaTeX math in your html pages.
Version: 0.2, 2007-04-01, Luca Allulli
Version: 0.2.1, 2007-02-01, Daniele "MadMage" Calisi
Version: 0.5.1, 2007-06-08, Americo Dias
Version: 0.5.2, 2007-11-01, Yacoby

Authors: Luca Allulli, Americo Dias
	http://www.amdias.com

License: CC-GNU LGPL
	http://creativecommons.org/licenses/LGPL/2.1/

MODx version: 0.9.5

See mimeTeX.txt for details.
 */
 
/* <?php */

// Please install mimetex CGI on your own server and update the following line.
$mimetex_url = 'http://www.example.com/cgi-bin/mimetex.cgi';

// Change the following line if you want to change the cache formulas. Don't forget to have write permitions!
$cache_folder = 'assets/cache/';

// Grab and evluate the document event.
$mdStrEvent = &$modx->Event;

if ( $mdStrEvent->name == "OnWebPagePrerender" ){
			
	// Grab the raw document output.
	$mdStrDocOutput = $modx->documentOutput;

	// Search the raw document output for blocks to be parsed. Those blocks are marked with <markdown> and </markdown> tags.
	preg_match_all( "|<pre class=\"math\">(.*)</pre>|Uis", $mdStrDocOutput, $mdArrParseBlocks);

	// Get the parsed output for each block.

	// If no blocks found, exit
	if( count($mdArrParseBlocks) == 0 ){
		return;
	}
						
	// Process the formulas...
	for ( $i=0; $i<count( $mdArrParseBlocks[0] ); $i++ ){
		$mdBlock = $mdArrParseBlocks[0][$i];
			
		// Create a unique formula filename using the formula text and MD5
		$formula_text = $mdArrParseBlocks[1][$i];
		$formula_hash = md5($formula_text);
		$formula_filename = 'etx_'.$formula_hash.'.gif';
			
		$cache_formula_path = $modx->config['base_path'] . $cache_folder . $formula_filename;
		$cache_formula_url = $modx->config['site_url'] . $cache_folder . $formula_filename;
			
		// Is the formula image cached?
		if (!is_file($cache_formula_path)){
			// If not, create the image
			$mimetex_host = curl_init($mimetex_url . '?formdata=' . urlencode($formula_text));

			// and save it to the cache path
			$cache_file = fopen($cache_formula_path, 'w');
			curl_setopt($mimetex_host, CURLOPT_FILE, $cache_file);
			curl_setopt($mimetex_host, CURLOPT_HEADER, 0);
			curl_exec($mimetex_host);
			curl_close($mimetex_host);
			fclose($cache_file);
		}
			
		$mdBlockText = '<img src="' . $cache_formula_url . '" alt="'.$formula_text.'"  border=0 align=middle>';
		$mdStrDocOutput = str_replace( $mdBlock, $mdBlockText, $mdStrDocOutput );
	}

	// Overwrite the raw document output with parsed one.
	$modx->documentOutput = $mdStrDocOutput;
}
/* ?> */