PHP学习笔记（4）GD库画五角星

    

 <?php
     //加header头，不然浏览器乱码
     header("content-type: image/png");
     //创建画布资源
    $img = imagecreatetruecolor(500, 500);
    //创建颜色
    $green = imagecolorallocate($img, 0, 255, 0);
    //画椭圆
    // imagefilledellipse($img, 200, 200, 100, 100, $green);
    $r = 100;//半径
    $degree36 = deg2rad(36);//直角三角形18度，改成弧度
    $l = 2*$r*sin($degree36);
    $a = $l*cos($degree36);//长边1长度
    $b = $l*sin($degree36);//短边1长度
    $c = $l/2;//短边2长度
    $d = $r*cos($degree36);//长边2长度
    //五个顶点坐标
    $px1 = 200;
    $py1 = 200;
    $px2 = $px1+$a;
    $py2 = $py1+$b;
    $px3 = $px1+$c;
    $py3 = $py1+$r+$d;
    $px4 = $px1-$c;
    $py4 = $py1+$r+$d;
    $px5 = $px1-$a;
    $py5 = $py1+$b;
     //画多边形，points是顶点坐标数组，num_points是顶点个数,妈蛋这个画不出来五角星，只能拼出来。还不如用直线画
    $points = array($px1,$py1,$px2,$py2,$px3,$py3,$px4,$py4,$px5,$py5);
    // imagepolygon($img, $points, 5, $green);
    //画五条线
    imageline($img, $px1, $py1, $px3, $py3, $green);
    imageline($img, $px1, $py1, $px4, $py4, $green);
    imageline($img, $px2, $py2, $px4, $py4, $green);
    imageline($img, $px2, $py2, $px5, $py5, $green);
    imageline($img, $px3, $py3, $px5, $py5, $green);
 
    //输出画布图像，终于正常了！
     imagepng($img);
 
 ?>