php gd库处理微信头像为圆形

function yuanjiao($imgpath) {
    $ext = pathinfo($imgpath);
    $src_img = null;
    switch ($ext['extension']) {
        case 'jpg':
            $src_img = imagecreatefromjpeg($imgpath);
            break;
        case 'png':
            $src_img = imagecreatefrompng($imgpath);
            break;
    }
    $wh = getimagesize($imgpath);
    $w = $wh[0];
    $h = $wh[1];
    $w = min($w, $h);
    $h = $w;
    $img = imagecreatetruecolor($w, $h);
    //这一句一定要有
    imagesavealpha($img, true);
    //拾取一个完全透明的颜色,最后一个参数127为全透明
    $bg = imagecolorallocatealpha($img, 255, 255, 255, 127);
    imagefill($img, 0, 0, $bg);
    $r = $w / 2; //圆半径
    $y_x = $r; //圆心X坐标
    $y_y = $r; //圆心Y坐标
    for ($x = 0; $x < $w; $x++) {
        for ($y = 0; $y < $h; $y++) {
            $rgbColor = imagecolorat($src_img, $x, $y);
            if (((($x - $r) * ($x - $r) + ($y - $r) * ($y - $r)) < ($r * $r))) {
                imagesetpixel($img, $x, $y, $rgbColor);
            }
        }
    }
    return $img;
}