PHP class to implement Chinese circular seal

/*
 * Chinese round seal category
 * @author lkk/lianq.net
 * @create on 10:03 2012-5-29
 * @example:
 * $seal = new circleSeal('You and I sit and walk east, west, north, south, center',75,6,24,0,0,16,40);
 * $seal->doImg();
 */

class circleSeal {
 private $sealString; //Seal characters
 private $strMaxLeng; //Maximum character length
 private $sealRadius; //Seal radius
 private $rimWidth; //Border thickness
 private $innerRadius; //Inner circle radius
 private $startRadius ; //Pentagram radius
 private $startAngle; //Pentagram tilt angle
 private $backGround; //Seal color
 private $centerDot; //Circle center coordinates
 private $img; //Graphic resource handle
 private $font; //Specified font
 private $fontSize; //Specified font size
 private $width; //Picture width
 private $height; //Picture height
 private $points; //Coordinates of each point of the five-pointed star
 private $charRadius; //String radius
 private $charAngle; //String tilt angle
 private $spacing; //Character spacing angle

 //Construction method
 public function __construct($str ='', $rad = 75, $rmwidth = 6, $strad = 24, $stang = 0, $crang = 0, $fsize = 16, $inrad =0){
 $this->sealString = empty($str) ? 'Seal test string' : $str;
 $this->strMaxLeng = 12;
 $this->sealRadius = $rad;
 $this->rimWidth = $rmwidth;
 $this->startRadius = $strad;
 $this- >startAngle = $stang;
 $this->charAngle = $crang;
 $this->centerDot = array('x'=>$rad, 'y'=>$rad);
 $this ->font = dirname(__FILE__) .'/simkai.ttf';
 $this->fontSize = $fsize;
 $this->innerRadius = $inrad; //Default 0, no
 $this-> ;spacing = 1;
 }

 //Create image resources
 private function createImg(){
 $this->width = 2 * $this->sealRadius;
 $this->height = 2 * $this ->sealRadius;
 $this->img = imagecreate($this->width, $this->height);
 imagecolorresolvealpha($this->img,255,255,255,127);
 $this->backGround = imagecolorallocate($this->img,255,0,0);
 }

 //Draw the seal border
 private function drawRim(){
 for($i=0;$i<$this->rimWidth ;$i++){
 imagearc($this->img,$this->centerDot['x'],$this->centerDot['y'],$this->width - $i,$ this->height - $i,0,360,$this->backGround);
 }
 }

 //Draw an inner circle
 private function drawInnerCircle(){
 imagearc($this->img,$this- >centerDot['x'],$this->centerDot['y'],2*$this->innerRadius,2*$this->innerRadius,0,360,$this->backGround);
 }

 //Draw a string
 private function drawString(){
 //Encoding processing
 $charset = mb_detect_encoding($this->sealString);
 if($charset != 'UTF-8'){
 $ this->sealString = mb_convert_encoding($this->sealString, 'UTF-8', 'GBK');
 }

 //Related measurement
 $this->charRadius = $this->sealRadius - $ this->rimWidth - $this->fontSize; //String radius
 $leng = mb_strlen($this->sealString,'utf8'); //String length
 if($leng > $this ->strMaxLeng) $leng = $this->strMaxLeng;
 $avgAngle = 360 / ($this->strMaxLeng); //Average character tilt

 //Split and write string
 $words = array(); //Character array
 for($i=0;$i<$leng;$i++){
 $words[] = mb_substr($this->sealString,$i,1,'utf8' );
 $r = 630 + $this->charAngle + $avgAngle*($i - $leng/2) + $this->spacing*($i-1); //Coordinate angle
 $R = 720 - $this->charAngle + $avgAngle*($leng-2*$i-1)/2 + $this->spacing*(1-$i); //Character angle
 $x = $this ->centerDot['x'] + $this->charRadius * cos(deg2rad($r)); //The x coordinate of the character
 $y = $this->centerDot['y'] + $this ->charRadius * sin(deg2rad($r)); //The y coordinate of the character
 imagettftext($this->img, $this->fontSize, $R, $x, $y, $this-> ;backGround, $this->font, $words[$i]);
 }
 }

    //画五角星
    private function drawStart(){
        $ang_out = 18 + $this->startAngle;
        $ang_in  = 56 + $this->startAngle;
        $rad_out = $this->startRadius;
        $rad_in  = $rad_out * 0.382;
        for($i=0;$i<5;$i++){
            //五个顶点坐标
            $this->points[] = $rad_out * cos(2*M_PI/5*$i - deg2rad($ang_out)) + $this->centerDot['x'];
            $this->points[] = $rad_out * sin(2*M_PI/5*$i - deg2rad($ang_out)) + $this->centerDot['y'];

            //内凹的点坐标
            $this->points[] = $rad_in * cos(2*M_PI/5*($i+1) - deg2rad($ang_in)) + $this->centerDot['x'];
            $this->points[] = $rad_in * sin(2*M_PI/5*($i+1) - deg2rad($ang_in)) + $this->centerDot['y'];
        }
        imagefilledpolygon($this->img, $this->points, 10, $this->backGround);
    }

    //输出
    private function outPut(){
        header('Content-type:image/png');
        imagepng($this->img);
        imagedestroy($this->img);
    }

    //对外生成
    public function doImg(){
        $this->createImg();
        $this->drawRim();
        $this->drawInnerCircle();
        $this->drawString();
        $this->drawStart();
        $this->outPut();
    }
}

PHP