Mine

<?php

$win = new GtkWindow();
$win->set_title('GtkDiff');
$win->connect_simple('destroy', array('gtk', 'main_quit'));
$vbox = new GtkVBox();

$filehbox = new gtkhbox();
$filevbox1 = new gtkvbox();
$filevbox2 = new gtkvbox();
$filevbox3 = new gtkvbox();

$oldlabel = new GtkLabel('Old file');
$oldfile = new GtkEntry();
$oldlocate = new GtkButton('Locate');
$oldlocate->connect_simple('clicked','open',$oldfile);

$newlabel = new GtkLabel('New file');
$newfile = new GtkEntry();
$newlocate = new GtkButton('Locate');
$newlocate->connect_simple('clicked','open',$newfile);

$filehbox->pack_start($filevbox1,false,false);
$filehbox->pack_start($filevbox2);
$filehbox->pack_start($filevbox3,false,false);
$filevbox1->pack_start($oldlabel);
$filevbox1->pack_start($newlabel);
$filevbox2->pack_start($oldfile);
$filevbox2->pack_start($newfile);
$filevbox3->pack_start($oldlocate);
$filevbox3->pack_start($newlocate);

$patchscroll = new GtkScrolledWindow();
$patch = new GtkTextView();
$patchscroll->add_with_viewport($patch);
$vbox->pack_start($filehbox,false,false);
$vbox->pack_start($patchscroll);
$create = new GtkButton('Create');
$create->connect_simple('clicked', 'create_patch',$oldfile,$newfile,$patch);
$save = new GtkButton('Save');
$bhbox = new GtkHBox();
$bhbox->pack_start($create);
$bhbox->pack_start($save);
$save->set_sensitive(false);
$vbox->pack_start($bhbox,false,false);
$win->add($vbox);
$win->show_all();
Gtk::main();

function create_patch($oldfile,$newfile,$patch){
	$old = $oldfile->get_text();
	$new = $newfile->get_text();
	if (file_exists($old) && file_exists($new)) {
		$old = file_get_contents($old);
		$new = file_get_contents($new);
		$buffer = $patch->get_buffer();
		$buffer->set_text(PHPDiff($old,$new));
	}
}

function open($file) {
	$dialog = new GtkFileChooserDialog("File Open", null, Gtk::FILE_CHOOSER_ACTION_OPEN,
	array(Gtk::STOCK_OK, Gtk::RESPONSE_OK), null);
	$dialog->show_all();
	if ($dialog->run() == Gtk::RESPONSE_OK) {
		$selected_file = $dialog->get_filename();
		$file->set_text($selected_file);
	}
	$dialog->destroy();
}

function PHPDiff($old,$new) {
	# split the source text into arrays of lines
	$t1 = explode("\n",$old);
	$x=array_pop($t1);
	if ($x>'') $t1[]="$x\n\\ No newline at end of file";
	$t2 = explode("\n",$new);
	$x=array_pop($t2);
	if ($x>'') $t2[]="$x\n\\ No newline at end of file";

	# build a reverse-index array using the line as key and line number as value
	# don't store blank lines, so they won't be targets of the shortest distance
	# search
	foreach($t1 as $i=>$x) if ($x>'') $r1[$x][]=$i;
	foreach($t2 as $i=>$x) if ($x>'') $r2[$x][]=$i;

	$a1=0; $a2=0;   # start at beginning of each list
	$actions=array();

	# walk this loop until we reach the end of one of the lists
	while ($a1<count($t1) && $a2<count($t2)) {
		# if we have a common element, save it and go to the next
		if ($t1[$a1]==$t2[$a2]) { $actions[]=4; $a1++; $a2++; continue; }

		# otherwise, find the shortest move (Manhattan-distance) from the
		# current location
		$best1=count($t1); $best2=count($t2);
		$s1=$a1; $s2=$a2;
		while(($s1+$s2-$a1-$a2) < ($best1+$best2-$a1-$a2)) {
			$d=-1;
			foreach((array)@$r1[$t2[$s2]] as $n)
			if ($n>=$s1) { $d=$n; break; }
			if ($d>=$s1 && ($d+$s2-$a1-$a2)<($best1+$best2-$a1-$a2))
			{ $best1=$d; $best2=$s2; }
			$d=-1;
			foreach((array)@$r2[$t1[$s1]] as $n)
			if ($n>=$s2) { $d=$n; break; }
			if ($d>=$s2 && ($s1+$d-$a1-$a2)<($best1+$best2-$a1-$a2))
			{ $best1=$s1; $best2=$d; }
			$s1++; $s2++;
		}
		while ($a1<$best1) { $actions[]=1; $a1++; }  # deleted elements
		while ($a2<$best2) { $actions[]=2; $a2++; }  # added elements
	}

	# we've reached the end of one list, now walk to the end of the other
	while($a1<count($t1)) { $actions[]=1; $a1++; }  # deleted elements
	while($a2<count($t2)) { $actions[]=2; $a2++; }  # added elements

	# and this marks our ending point
	$actions[]=8;

	# now, let's follow the path we just took and report the added/deleted
	# elements into $out.
	$op = 0;
	$x0=$x1=0; $y0=$y1=0;
	$out = array();
	foreach($actions as $act) {
		if ($act==1) { $op|=$act; $x1++; continue; }
		if ($act==2) { $op|=$act; $y1++; continue; }
		if ($op>0) {
			$xstr = ($x1==($x0+1)) ? $x1 : ($x0+1).",$x1";
			$ystr = ($y1==($y0+1)) ? $y1 : ($y0+1).",$y1";
			if ($op==1) $out[] = "{$xstr}d{$y1}";
			elseif ($op==3) $out[] = "{$xstr}c{$ystr}";
			while ($x0<$x1) { $out[] = '< '.$t1[$x0]; $x0++; }   # deleted elems
			if ($op==2) $out[] = "{$x1}a{$ystr}";
			elseif ($op==3) $out[] = '---';
			while ($y0<$y1) { $out[] = '> '.$t2[$y0]; $y0++; }   # added elems
		}
		$x1++; $x0=$x1;
		$y1++; $y0=$y1;
		$op=0;
	}
	$out[] = '';
	return join("\n",$out);
}

?>