怎么使用php的gd库画一条抗锯齿的粗斜线

<?php//error_reporting(E_ALL ^ E_NOTICE);class Graph {  /**   * 伪3D绘图类   */  var $im;  var $type = "gif"; // png,gif,jpeg,wbmp  var $xo;  var $yo;  var $color;  var $fillcolor;  var $filldarkcolor;  var $filltype = true;  var $orgx;  var $orgy;  var $viewx;  var $viewy;  var $winx;  var $winy;  var $extx = 1;  var $exty = -1;  var $ksin;  var $kcos;  function Graph() {    if(func_num_args() == 2)        $this->create(func_get_arc(0),func_get_arc(1));    else        $this->create(400,300);  }  /**   * 在($x,$y)处画点   */  function pixel($x,$y) {    $p = $this->get_view($x,$y);    imagesetpixel($this->im,$p['x'],$p['y'],$this->color);    $this->xo = $p['x'];    $this->yo = $p['y'];  }  /**   * 移动到($x,$y)处   */  function moveto($x,$y) {    $p = $this->get_view($x,$y);    $this->xo = $p['x'];    $this->yo = $p['y'];  }  /**   * 从($x1,$y1)到($x2,$y2)处画线   */  function line($x1,$y1,$x2,$y2) {    $p1 = $this->get_view($x1,$y1);    $p2 = $this->get_view($x2,$y2);    imageline($this->im,$p1['x'],$p1['y'],$p2['x'],$p2['y'],$this->color);  }  /**   * 从当前位置到($x,$y)处画线   */  function lineto($x,$y) {    $p = $this->get_view($x,$y);    imageline($this->im, $this->xo, $this->yo, $p['x'], $p['y'], $this->color);    $this->xo = $p['x'];    $this->yo = $p['y'];  }  /**   * 设置当前颜色   */  function color($clr) {    $r = ($clr>>16) & 0xff;     $g = ($clr>>8) & 0xff;     $b = ($clr) & 0xff;     $this->color = ImageColorAllocate($this->im, $r,$g,$b);    $this->fillcolor = ImageColorAllocate($this->im, $r,$g,$b);    $this->filldarkcolor = ImageColorAllocate($this->im, $r/2,$g/2,$b/2);    return $this->color;  }  /**   * 设置当前充填颜色   */  function fillcolor($clr) {    $r = ($clr>>16) & 0xff;     $g = ($clr>>8) & 0xff;     $b = ($clr) & 0xff;     $this->fillcolor = ImageColorAllocate($this->im, $r,$g,$b);    return $this->fillcolor;  }  /**   * 创建GD句柄并设置坐标系   */  function create($x,$y) {    $this->im = imagecreatetruecolor($x,$y);imageantialias($this->im, 1);imagefill($this->im, 0, 0, $this->color(0xffffff));    $this->viewx = $x-1;    $this->viewy = -($y-1);    $this->winx = $x;    $this->winy = $y;    $this->orgx = 0;    $this->orgy = 0;//$y;    $this->colors = $this->color(0xffffff);    settype($this->ksin,"double");    settype($this->kcos,"double");    $this->ksin = sin(deg2rad(0));    $this->kcos = cos(deg2rad(0));  }  /**   * 坐标映射   */  function get_view($x,$y) {    $this->xo = $x*$this->kcos - $y*$this->ksin;    $this->yo = $x*$this->ksin + $y*$this->kcos;    $p['x'] = ($this->xo + $this->orgx)*($this->viewx/$this->winx);    $p['y'] = ($this->yo + $this->orgy)*($this->viewy/$this->winy)-$this->viewy;    return $p;  }  /**   * 设置限度   */  function set_ext($x,$y=0) {    $this->winx = $x;    if($y == 0) {        $this->winy = - $x * $this->viewy / $this->viewx;    }else {        $this->winy = $y;    }  }  /**   * 设置旋转角   */  function set_r($p) {    $this->ksin = sin(deg2rad($p));    $this->kcos = cos(deg2rad($p));  }  /**   * 构造图形，必需在派生类中重载本方法   */  function paint() {    /**     * 必需由派生类重载     * 必需包含语句 $this->create(宽度,高度);     */    die("paint 方法必需由派生类重载!");  }  /**   * 输出图形   */  function run() {    $this->paint();    $func = "Image".$this->type;    if(! function_exists($func)) {        $this->type = "png";        $func = "Image".$this->type;    }    Header("Content-type: image/{$this->type}");    $func($this->im);    imageDestroy($this->im);  }  /**   * 圆类图形数据生成，参数$p为坐标旋转角   */  function get_point($ox,$oy,$w,$h,$start,$end) {    $a = $w/2;    $b = $h/2;    $rs = array();    $i = $start;    for($i=$start;$i<=$end;$i+=5) {        $n = deg2rad($i);        $x = $a*cos($n);        $y = $b*sin($n);        $p = $this->get_view($ox+$x,$oy+$y);        $rs[] = $p['x'];        $rs[] = $p['y'];        if($i == $end) break;        if($i+5 > $end) $i = $end - 5;    }    $p = $this->get_view($ox,$oy);    $rs[] = $p['x'];    $rs[] = $p['y'];    $rs[] = $rs[0];    $rs[] = $rs[1];    return $rs;  }  /**   * 弓形   */  function chord($left,$top,$w,$h,$start,$end,$z=0) {    $ar = $this->get_point($left,$top,$w,$h,$start,$end,$p);    for($i=0;$i<count($ar);$i+=2) {        $p = $this->get_view($ar[$i],$ar[$i+1]);        $ar[$i] = $p['x'];        $ar[$i+1] = $p['y'];    }    imagefilledpolygon($this->im,$ar,count($ar)/2-1,$this->fillcolor);    imagepolygon($this->im,$ar,count($ar)/2-1,$this->color);  }  /**   * 扇形   */  function pie($left,$top,$w,$h,$start,$end,$z=0) {    $this->get_view($left,$top+$z);    $ar = $this->get_point($left,$top+$z,$w,$h,$start,$end);    $this->get_view($left,$top);    $arh = $this->get_point($left,$top,$w,$h,$start,$end);    for($j=0;$j<count($ar)-2;$j+=2) {        $t= array($ar[$j],$ar[$j+1],$ar[$j+2],$ar[$j+3],$arh[$j+2],$arh[$j+3],$arh[$j],$arh[$j+1]);        if($this->filltype)            imagefilledpolygon($this->im,$t,4,$this->filldarkcolor);        else            imagepolygon($this->im,$t,4,$this->color);    }    if($this->filltype)        imagefilledpolygon($this->im,$ar,count($ar)/2-1,$this->fillcolor);  }  /**   * 弧形   */  function arc($left,$top,$w,$h,$start,$end,$z=0) {    $ar = $this->get_point($left,$top,$w,$h,$start,$end,$p);    $this->moveto($ar[0],$ar[1]);    for($i=2;$i<count($ar)-2;$i+=2)        $this->lineto($ar[$i],$ar[$i+1]);  }}/** * 重载基类的paint方法 */class myGraph extends Graph {  function paint() {//    $this->create(400,300);    $this->create(200,150);$this->set_ext(400);    $this->set_r(10); // 旋转    $this->filltype = false; //充填    $k = 40;    //高    $a =200;    //中心x    $b = 150;    //中心y    $c = 200;    //长轴    $d = 100;    //短轴    $this->color(0x000000);    $this->color(0xff0000);    $this->pie($a,$b,$c,$d,0,100,$k);    $this->color(0x00ff00);    $this->pie($a,$b,$c,$d,120,240,$k);    $this->color(0x0000ff);    $this->pie($a+10,$b-10,$c,$d,240,360,$k);    $this->color(0x8080ff);    $this->pie(50,80,40,20,0,360,50);    $this->line($a,0,$a,$b*2);    $this->line(0,$b,$a*2,$b);  }}$g = new myGraph;$g->run();