php-gd2 生成圖片-限制每行字數

$str = 'aa212asda薩達aa212asda薩達aa212asda達';
$len = mb_strlen( $str );
$arr = [];
$sum = 0 ;
$max_width = 100;
$number_px = 5;
$English_px = 5;
$chinese_px = 10;
$all = '';
for( $i = 0 ; $i < $len ; $i ++  ){
    $char = mb_substr( $str ,$i , 1 );
    if( is_numeric( $char )  ){
        $sum += $number_px;
    }else if( preg_match('/^([a-zA-Z]){1}$/', $char ) ){
        $sum += $zimu_px;
    }else{
        $sum += $chinese_px;
    }
    $all .= $char;
    if( $max_width - $sum < $English_px || $max_width - $sum < $chinese_px ){
        $arr[] = $all;
        $all = '';
        $sum = 0;
    }
}
$arr[] = $all;
echo '<pre/>';
print_r($arr);
exit;