Nice Add-on!
If you aren't using the first post ad location, that's a great place to put this..
Edit the QR Code plugin and put this code at the end BEFORE the }..
Code:
$template_hook['share_this_thread'] = $threadinfo['qr'];
Also, change the hook from showthread_complete to showthread_postbit_create
Then in ACP->Advertising, click Add New Ad, select 'Thread' and click on First Post Content.
Title: Share This Thread
Ad HTML:
Code:
<div align="center">Share This Thread<br />
{vb:raw template_hook.share_this_thread}</div>
Active: Yes
Click Save and you're all set.
You may need to edit ad_margin, ad_padding and ad_maxWidth in stylevars for it to display properly.