PHP class to implement Chinese circular seal

<?php
/*
 * 中文圆形印章类
 * @author lkk/lianq.net
 * @example:
 *  $seal = new circleSeal(&#39;你我他坐站走东西南北中&#39;,75,6,24,0,0,16,40);
 *  $seal->doImg();
 */
 
class circleSeal {
    private $sealString;    //印章字符
    private $strMaxLeng;    //最大字符长度
    private $sealRadius;    //印章半径
    private $rimWidth;      //边框厚度
    private $innerRadius;   //内圆半径
    private $startRadius;   //五角星半径
    private $startAngle;    //五角星倾斜角度
    private $backGround;    //印章颜色
    private $centerDot;     //圆心坐标
    private $img;           //图形资源句柄
    private $font;          //指定的字体
    private $fontSize;      //指定字体大小
    private $width;         //图片宽度
    private $height;        //图片高度
    private $points;        //五角星各点坐标
    private $charRadius;    //字符串半径
    private $charAngle;     //字符串倾斜角度
    private $spacing;       //字符间隔角度
 
    //构造方法
    public function __construct($str =&#39;&#39;, $rad = 75, $rmwidth = 6, $strad = 24, $stang = 0, $crang = 0, $fsize = 16, $inrad =0){
        $this->sealString   = empty($str) ? &#39;印章测试字符串&#39; : $str;
        $this->strMaxLeng   = 12;
        $this->sealRadius   = $rad;
        $this->rimWidth     = $rmwidth;
        $this->startRadius  = $strad;
        $this->startAngle   = $stang;
        $this->charAngle    = $crang;
        $this->centerDot    = array(&#39;x&#39;=>$rad, &#39;y&#39;=>$rad);
        $this->font         = dirname(__FILE__) .&#39;/simkai.ttf&#39;;
        $this->fontSize     = $fsize;
        $this->innerRadius  = $inrad;   //默认0,没有
        $this->spacing      = 1;
    }
 
    //创建图片资源
    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);
    }
 
    //画印章边框
    private function drawRim(){
        for($i=0;$i<$this->rimWidth;$i++){
            imagearc($this->img,$this->centerDot[&#39;x&#39;],$this->centerDot[&#39;y&#39;],$this->width - $i,$this->height - $i,0,360,$this->backGround);
        }
    }
 
    //画内圆
    private function drawInnerCircle(){
        imagearc($this->img,$this->centerDot[&#39;x&#39;],$this->centerDot[&#39;y&#39;],2*$this->innerRadius,2*$this->innerRadius,0,360,$this->backGround);
    }
 
    //画字符串
    private function drawString(){
        //编码处理
        $charset = mb_detect_encoding($this->sealString);
        if($charset != &#39;UTF-8&#39;){
            $this->sealString = mb_convert_encoding($this->sealString, &#39;UTF-8&#39;, &#39;GBK&#39;);
        }
 
        //相关计量
        $this->charRadius = $this->sealRadius - $this->rimWidth - $this->fontSize;  //字符串半径
        $leng   = mb_strlen($this->sealString,&#39;utf8&#39;);  //字符串长度
        if($leng > $this->strMaxLeng) $leng = $this->strMaxLeng;
        $avgAngle   = 360 / ($this->strMaxLeng);    //平均字符倾斜度
 
        //拆分并写入字符串
        $words  = array();  //字符数组
        for($i=0;$i<$leng;$i++){
            $words[] = mb_substr($this->sealString,$i,1,&#39;utf8&#39;);
            $r = 630 + $this->charAngle + $avgAngle*($i - $leng/2) + $this->spacing*($i-1);     //坐标角度
            $R = 720 - $this->charAngle + $avgAngle*($leng-2*$i-1)/2 + $this->spacing*(1-$i);   //字符角度
            $x = $this->centerDot[&#39;x&#39;] + $this->charRadius * cos(deg2rad($r));  //字符的x坐标
            $y = $this->centerDot[&#39;y&#39;] + $this->charRadius * sin(deg2rad($r));  //字符的y坐标
            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[&#39;x&#39;];
            $this->points[] = $rad_out * sin(2*M_PI/5*$i - deg2rad($ang_out)) + $this->centerDot[&#39;y&#39;];
 
            //内凹的点坐标
            $this->points[] = $rad_in * cos(2*M_PI/5*($i+1) - deg2rad($ang_in)) + $this->centerDot[&#39;x&#39;];
            $this->points[] = $rad_in * sin(2*M_PI/5*($i+1) - deg2rad($ang_in)) + $this->centerDot[&#39;y&#39;];
        }
        imagefilledpolygon($this->img, $this->points, 10, $this->backGround);
    }
 
    //输出
    private function outPut(){
        header(&#39;Content-type:image/png&#39;);
        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();
    }
}