I wanted to be able to show who had participated in a given thread within the thread. This is available via WHOREAD in the forum listing, but it didn't feel as intuitive. Now, users can see immediately who's posted in a given thread.

What's involved:
1. Create a plugin
2. Create a template to display plugin info
3. Create a replacement variable
4. Edit SHOWTHREAD to call the template

Creating the plugin
This is pretty much a straight copy of the code from misc.php into a plugin, and registering the variable (thanks Lynne).
1. Admincp > Plugins & Products > Add New Plugin
Product: Vbulletin
Title: Who Posted in Showthread
Hook Location: showthread_start
Execution Order: 5
scription">PHP- Kodu:
if (!$threadinfo['threadid'] OR $threadinfo['isdeleted'] OR (!$threadinfo['visible'] AND !can_moderate($threadinfo['forumid'], 'canmoderateposts'))) 
standard_error(fetch_error('invalidid'$vbphrase['thread'], $vbulletin->options['contactuslink'])));  

$hook vBulletinHook::fetch_hook('misc_whoposted_start')) ? eval($hook) : false

$posts $db->query_read_slave("  
        SELECT COUNT(postid) AS posts,  
            post.username AS postuser,user.userid,user.username  
        FROM " 
TABLE_PREFIX "post AS post  
        LEFT JOIN " 
TABLE_PREFIX "user AS user USING(userid)  
        WHERE threadid = 
            AND visible = 1  
        GROUP BY userid  
        ORDER BY posts DESC  

$totalposts 0;  
$posters '';  
    if (
DIR '/includes/functions_bigthree.php');  
        while (
$post $db->fetch_array($posts))  
// hide users in Coventry  
$ast '';  
            if (
in_coventry($post['userid']) AND !can_moderate($threadinfo['forumid'])) 

            if (
$post['username'] == '')  
$post['username'] = $post['postuser'];  
$post['username'] .=  $ast;  
$totalposts += $post['posts'];  
$post['posts'] = vb_number_format($post['posts']);  
$show['memberlink'] = iif ($post['userid'], truefalse);  
$templater vB_Template::create('showthreadwhoposted');  
$posters .= $templater->render();  
$totalposts vb_number_format($totalposts);  

$hook vBulletinHook::fetch_hook('misc_whoposted_complete')) ? eval($hook) : false
vB_Template::preRegister('SHOWTHREAD', array('posters' => $posters));   
Plugin is Active: Yes

Creating the template
Sharp eyes will have caught that the template is going to be named "showthreadwhoposted". I'm super original like that.
1. Styles and Templates > Style Manager > Add New Template
Title: showthreadwhoposted
description">PHP- Kodu:
<div style="margin-right: 3px; float: right; margin-bottom: 3px; max-width: 30px; overflow: hidden;"
a href="{vb:link member, {vb:raw post}}" title="{vb:raw post.username}"
img height="30" src="http://nwod.org/forum/image.php?u={vb:link member, {vb:raw post}}"  />                                     
Note that this template creates 30px avatars that float. You can choose to make a simple list of username links, or resize the avatars, however you like. This is just how I wanted them displayed.

Create a replacement variable
Vbulletin isn't super helpful when it comes to calling avatars by username instead of userids, so we had to get a little bit hacky in the template above. This bit right here:
"http://nwod.org/forum/image.php?u={vb:link member, {vb:raw post}}"
Needs to be cleaned up.
1. Styles and Templates > Replacement Variable Manager > Add New Replacement Variable
Search for Text: image.php?u=member.php?
Replace with Text: image.php?u=

This strips out the raw link we called, leaving us with just the userid. If someone knows of a better way to call the userid, this might not be necessary and the Template could be edited.

Edit SHOWTHREAD to call the template
We've made the plugin fetch who's posted, rendered it into a template, and cleaned up the avatar image URL in said template. Now we just need to place the display of users who posted in the SHOWTHREAD template.
1. Search in Templates > SHOWTHREAD (search Titles only) > Find
2. Search for the first occurence of "<vb:if condition="$pagenav">". This will position our list above the pagination and tools menu bar.
3. Add the following:
PHP- Kodu:
        <div style="float: right; margin-top: 3px;"
vbraw posters
This will create a floating list of posters.

If everything has been done properly you should see something like this:

My SHOWTHREAD is modified a bit, but you get the general idea. Right above the pagination is a list of avatars that link to the member's page.

Happy forum'ing!

Original Source: Who Posted in SHOWTHREAD