php绘制中文的乱码有关问题

php绘制中文的乱码问题

PHP code

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<?php //    1.
        $img=imagecreatetruecolor(400,400);
        
        $white=imagecolorallocate($img, 255, 255, 255);
        $gray=imagecolorallocate($img, 0xC0, 0xC0, 0xC0);
        $darkgray=imagecolorallocate($img, 0x90, 0x90, 0x90);
        $navy=imagecolorallocate($img, 0, 0, 0x80);
        $darknavy=imagecolorallocate($img, 0, 0, 0x50);
        $red=    imagecolorallocate($img, 0xFF, 0, 0);
        $darkred=imagecolorallocate($img, 0x90, 0, 0);
        
        
//     2.
        imagefill($img,0,0,$red);

        
        imagettftext($img,20,-60,60,150,$darknavy,"simhei.ttf","一二三");

        
        
        
        
//     3.
        header("Content-Type:image/gif");
        imagegif($img);
        
//     4.
        imagedestroy($img);
        

  "一二三"无法显示，只有几个方框，怎样解决乱码问题?先谢谢!!!

------解决方案--------------------
imagettftext($img,20,-60,60,150,$darknavy,"simhei.ttf", iconv('gbk', 'utf-8', "一二三") );