gistfile1.txt

function thai($x) {
	$back = array(
		"\xE0\xB9\x88" => "\xEF\x9C\x85",  //่(ไม้เอก)=>
		"\xE0\xB9\x89" => "\xEF\x9C\x86",  //้(ไม้โทร)=>
		"\xE0\xB9\x8A" => "\xEF\x9C\x87",  //๊(ไม้ตรี)=>
		"\xE0\xB9\x8B" => "\xEF\x9C\x88",  //+(ไม้จัตวา)=>
		"\xE0\xB9\x8C" => "\xEF\x9C\x89"   //์(ตัวการัน)=>
	);
	$cross = array();
        $payanchana=array(
                "\xE0\xB8\xB4",   //สระอิ
                "\xE0\xB8\xB5",   //สระอี
                "\xE0\xB8\xB6",   //สระอึ
                "\xE0\xB8\xB7",   //สระอือ
                "\xE0\xB8\xB1",   //ไม้หันอากาศ
                "ำ"              //สระอำ  \xE0\xB8\xB3
        );
        //http://www.endmemo.com/unicode/thai.php  อ้างอิง unicode
	foreach ($payanchana as $p) {
            
            if($p!='ำ'){
		for ($i = 0x85; $i <= 0x89; $i ++) {
			$from = $p . "\xEF\x9C" . chr($i);
			$to   = $p . "\xE0\xB9" . chr($i +3);
			$cross[$from] = $to;
   
		}
            }else{
                for ($i = 0x85; $i <= 0x89; $i ++) {
			$from = "\xEF\x9C" . chr($i).$p;
			$to   = "\xE0\xB9" . chr($i +3).$p;
			$cross[$from] = $to;
		}
            }
            
	}
        $x = strtr($x, $back);
        $x = strtr($x, $cross);
	
        
	return $x;
}

mpdf แก้สระลอย จากบทความนี้ https://gist.github.com/dtinth/716814/