实现代码很简单，通过二维码生成api接口生成二维码图片，然后检查保存二维码的qrcode目录下是否有同名的.jpg文件，没有就把生成的二维码图片保存到qrcode目录。

函数代码

function tddx_set_qr($url,$qrname){
	$path = ABSPATH . 'qrcode';
	set_time_limit (10);
	$destination_folder = $path?$path.'/':''; 
	$localname = $destination_folder .$qrname;     
	$file = fopen ($url, "rb");
	if ($file) {     
		$newf = fopen ($localname, "wb");
		if ($newf)     
			while(!feof($file)) {     
				fwrite( $newf, fread($file, 1024 * 2 ), 1024 * 2 );
			}     
	}     
	if ($file) {     
		fclose($file);
	}     
	if ($newf) {     
		fclose($newf);     
	}
}

function tddx_get_qr($url,$qrname){
	global $zbp;	
	$localqr =  ABSPATH .'/qrcode/'.$qrname.'.jpg';
	if (!is_file($localqr)) {
		second_set_qr( "http://api.qrserver.com/v1/create-qr-code/?size=200x200&data=".$url ,$qrname.".jpg");
	}
}

调用代码

tddx_get_qr('https://www.tddx.net','tddx')

扩展：其它免费API

https://my.tv.sohu.com/user/a/wvideo/getQRCode.do?text=https://www.tddx.net/&width=200&height=200