Texvc PHP Alternative

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Overview[edit]

Mediawiki uses an additional program, Texvc, to render math into nice images for page display. Unfortunately texvc needs to be compiled and is written in OCaml which can pose a problem on most public hosts even if all the other requirements are met (ghostscript, latex, etc). This work around replaces the Math rendering code with an in suite PHP version, performing all the image manipulations, renderings, etc that Texvc would normally do.

Limitations[edit]

This "hack" is not a workaround to get out of using "latex", "dvips", and "convert" (these three image processing unix commands are required) but it does workaround having to get access to installing ocaml and compiling texvc. While this hack does retain image caching, most of the other features available to math rendering have been lost and some slight differences do occur between the final output image. One notable difference is that only images are produced, the MyMCAT project didn't care for MathML or text outputs of formulas, thus these options were cut.

How it works[edit]

Basically, in Math.php, the rendering function has been striped of its calls to texvc and instead PHP makes all the calls to the necessary functions directly.

How to install it[edit]

Below is a copy of the source from Math.php. You will need to ensure you have a working directory and the shell commands work correctly for this to work. If you have tried to install texvc formerly, you should replace the Math.php in includes/Math.php. If it doesn't exist yet, you should probably create it with the contents below.

Note Note: The render function still passes arguments, but they are no longer read. If anyone wants to update this script with some more fancy features, please email me, I would love to hear about it.

<?php
/**
 * Contain everything related to <math> </math> parsing
 */

class MathRenderer {
	
	//shell programs:
	var $LATEX_PATH = "/usr/bin/latex";
	var $DVIPS_PATH = "/usr/bin/dvips";
	var $CONVERT_PATH = "/usr/bin/convert";
	
	//image url stuff
 	var $URL_PATH = "http://www.mymcat.com/testing/cache";

	var $tex = '';
	var $inputhash = '';
	var $hash = '';
	var $html = '';

	//right now we have NO params, but it might be worth keeping...
	function __construct( $tex, $params=array() ) {
		$this->tex = $tex;
		$this->params = $params;
 	}

	function render() {
		global $wgTmpDirectory;
		$fname = 'MathRenderer::render';

		if( !$this->_recall() ) {
			# Ensure that the temp and output directories are available before continuing...
			if( !file_exists( $wgTmpDirectory ) ) {
				if( !@mkdir( $wgTmpDirectory ) ) {
					return $this->_error( "wgTmpDirectory: $wgTmpDirectory does not exist! " );
				}
			} elseif( !is_dir( $wgTmpDirectory ) || !is_writable( $wgTmpDirectory ) ) {
				return $this->_error( "wgTmpDirectory: $wgTmpDirectory is not accessible!" );
			}

			if( function_exists( 'is_executable' ) && !is_executable( $this->LATEX_PATH ) ) {
				return $this->_error( "latex not found..." );
			}
			if( function_exists( 'is_executable' ) && !is_executable( $this->DVIPS_PATH ) ) {                                
                                return $this->_error( "dvips not found" );      
                        }	
			if( function_exists( 'is_executable' ) && !is_executable( $this->CONVERT_PATH ) ) {                                
                                return $this->_error( "convert (imagemagick) not found" );   
                        }


			//wrap the math text with the generic latex requirements
			//in the future, this wrapper should be modifyable by the parameters
			$thunk = $this->_wrap($this->tex);
			
			//begin working...
			$hash = md5($this->tex);
			$this->hash = $hash;
			wfDebug( "Math: hash is: $this->hash\n" );

			//get to the tmp dir:
			$current_dir = getcwd();
			chdir( $wgTmpDirectory );
			
			// create temporary LaTeX file
			$fp = fopen( "$hash.tex", "w+");
			fputs($fp, $thunk);
			fclose($fp);

			//run latex:
			$command = $this->LATEX_PATH . " --interaction=nonstopmode " . $hash . ".tex";
 			exec($command);
			wfDebug( "Math: latex command, $command\n" );

			//run dvips:
			$command = $this->DVIPS_PATH . " -E $hash" . ".dvi -o " .  "$hash.ps";
 			exec($command);
			wfDebug( "Math: dvips command, $command\n" );


			//run ps through imageMagick:
		 	$command = $this->CONVERT_PATH . " -density 120 $hash.ps $hash.png";
 			exec($command);
			wfDebug( "Math: convert command, $command\n" );

  	//		copy("$hash.png", $this->CACHE_DIR . "/$hash.png");
			chdir($current_dir);

			if (!preg_match("/^[a-f0-9]{32}$/", $this->hash)) {
				return $this->_error( "could not match the hash anywhere" );
			}

			if( !file_exists( "$wgTmpDirectory/{$this->hash}.png" ) ) {
				return $this->_error( 'math_image_error' . " $wgTmpDirectory/{$this->hash}.png  , $dirandhash , " . getcwd() );
			}

			$hashpath = $this->_getHashPath();
			if( !file_exists( $hashpath ) ) {
				if( !@wfMkdirParents( $hashpath, 0755 ) ) {
					return $this->_error( "hashpath error type one: $hashpath" );
				}
			} elseif( !is_dir( $hashpath ) || !is_writable( $hashpath ) ) {
				return $this->_error( 'hashpath error type two' );
			}

			if( !rename( "$wgTmpDirectory/{$this->hash}.png", "$hashpath/{$this->hash}.png" ) ) {
				return $this->_error( "hashpath rename failed" );
			}

			# Now save it back to the DB:
			if ( !wfReadOnly() ) {
				$outmd5_sql = pack('H32', $this->hash);

				$md5_sql = pack('H32', $this->md5); # Binary packed, not hex

				$dbw = wfGetDB( DB_MASTER );
				$dbw->replace( 'math', array( 'math_inputhash' ),
				  array(
					'math_inputhash' => $dbw->encodeBlob($md5_sql),
					'math_outputhash' => $dbw->encodeBlob($outmd5_sql),
					'math_html_conservativeness' => "",
					'math_html' => $this->html,
					'math_mathml' => "",
				  ), $fname, array( 'IGNORE' )
				);
			}
			
			$this->_cleanup( $hash );
		}
		
		return $this->_doRender();
	}

	function _error( $msg, $append = '' ) {
		$mf   = htmlspecialchars( wfMsg( 'math_failure' ) );
		$errmsg = htmlspecialchars( $msg );
		$source = htmlspecialchars( str_replace( "\n", ' ', $this->tex ) );
		return "<strong class='error'>$mf ($errmsg$append): $source</strong>\n";
	}

	function _wrap($thunk) {
  		return <<<EOS
    		\documentclass[10pt]{article}

	 	% add additional packages here
		\usepackage{amsmath}
		\usepackage{amsfonts}
		\usepackage{amssymb}
		\usepackage{pst-plot}
		\usepackage{color}

		\pagestyle{empty}
		\begin{document}
		\begin{equation*}
		\large
		$thunk
		\end{equation*}
		\end{document}
EOS;
	}


	function _cleanup($hash) {

		$current_dir = getcwd();
		chdir( $wgTmpDirectory );

		unlink($this->TMP_DIR . "/$hash.tex");
		unlink($this->TMP_DIR . "/$hash.aux");
		unlink($this->TMP_DIR . "/$hash.log");
		unlink($this->TMP_DIR . "/$hash.dvi");
		unlink($this->TMP_DIR . "/$hash.ps");
		unlink($this->TMP_DIR . "/$hash.png");

		chdir($current_dir);
	}

	function _recall() {
		global $wgMathDirectory;
		$fname = 'MathRenderer::_recall';

		$this->md5 = md5( $this->tex );
		$dbr = wfGetDB( DB_SLAVE );
		$rpage = $dbr->selectRow( 'math',
			array( 'math_outputhash','math_html_conservativeness','math_html','math_mathml' ),
			array( 'math_inputhash' => $dbr->encodeBlob(pack("H32", $this->md5))), # Binary packed, not hex
			$fname
		);

		if( $rpage !== false ) {
			# Tailing 0x20s can get dropped by the database, add it back on if necessary:
			$xhash = unpack( 'H32md5', $dbr->decodeBlob($rpage->math_outputhash) . "                " );
			$this->hash = $xhash ['md5'];

			$this->conservativeness = $rpage->math_html_conservativeness;
			$this->html = $rpage->math_html;
			$this->mathml = $rpage->math_mathml;

			if( file_exists( $this->_getHashPath() . "/{$this->hash}.png" ) ) {
				return true;
			}

			if( file_exists( $wgMathDirectory . "/{$this->hash}.png" ) ) {
				$hashpath = $this->_getHashPath();

				if( !file_exists( $hashpath ) ) {
					if( !@wfMkdirParents( $hashpath, 0755 ) ) {
						return false;
					}
				} elseif( !is_dir( $hashpath ) || !is_writable( $hashpath ) ) {
					return false;
				}
				if ( function_exists( "link" ) ) {
					return link ( $wgMathDirectory . "/{$this->hash}.png",
							$hashpath . "/{$this->hash}.png" );
				} else {
					return rename ( $wgMathDirectory . "/{$this->hash}.png",
							$hashpath . "/{$this->hash}.png" );
				}
			}

		}

		# Missing from the database and/or the render cache
		return false;
	}

	/**
	 * Select among PNG, HTML, or MathML output depending on
	 * THIS ONLY does PNG now...
	 */
	function _doRender() {
		return $this->_linkToMathImage();
	}
	
	function _attribs( $tag, $defaults=array(), $overrides=array() ) {
		$attribs = Sanitizer::validateTagAttributes( $this->params, $tag );
		$attribs = Sanitizer::mergeAttributes( $defaults, $attribs );
		$attribs = Sanitizer::mergeAttributes( $attribs, $overrides );
		return $attribs;
	}

	function _linkToMathImage() {
		global $wgMathPath;
		$url = "$wgMathPath/" . substr($this->hash, 0, 1)
					.'/'. substr($this->hash, 1, 1) .'/'. substr($this->hash, 2, 1)
					. "/{$this->hash}.png";

		return Xml::element( 'img',
			$this->_attribs(
				'img',
				array(
					'class' => 'tex',
					'alt' => $this->tex ),
				array(
					'src' => $url ) ) );
	}

	function _getHashPath() {
		global $wgMathDirectory;
		$path = $wgMathDirectory .'/'. substr($this->hash, 0, 1)
					.'/'. substr($this->hash, 1, 1)
					.'/'. substr($this->hash, 2, 1);
		wfDebug( "TeX: getHashPath, hash is: $this->hash, path is: $path\n" );
		return $path;
	}

	public static function renderMath( $tex, $params=array() ) {
		global $wgUser;
		$math = new MathRenderer( $tex, $params );
	//	$math->setOutputMode( $wgUser->getOption('math'));
		return $math->render();
	}
}

Known Bugs[edit]

Beyond the fact that parameters can't be passed to this renderer and the output sometimes looks slightly different than other latex renderings there are some other minor issues: - Sometimes PHP warnings get posted to the page when you render some math. I believe I am getting this because I do my file handling in /usr/temp which isn't the best place. This warning never shows up again the next time you go to the page and the image is still rendered just fine. - If you manually delete all the images in the cache folder you get warnings the first time Math.php needs to rerender them but again it renders fine and the warnings never show up again.

Texlive needed package[edit]

For those who doesn't know how tex works,if you use texlive for making working latex, you'll also have to install some packages:

  • "graphics"
  • "pst-plot"
  • "xkeyval"
  • "PSTricks",
  • "multido"

And maybe others depending on how you installed texlive.

Working Example[edit]

This work was done for MyMCAT. You can specifically see an example of the math rendered at The Railgun Passage.

Acknowledgments[edit]

This hack was based off of the linux journal article http://www.linuxjournal.com/article/7870 by Titus Barik.