Since I want to make a lot of instances (think prefabs), one of my goals has been to take some existing structures and trim them down to pretty much the bare minimum. So I'm working on doing this for the start of a coop map. I'm using a decompiled version of mp_coop_doors as a base, as it's nice and small. Trim everything down and it still loads in multiplayer (instead of #Valve_Reject_Server_Full). Trim some more and it still loads. Copy/paste it into a new map, save... and it doesn't load. Argh.

Well, it turns out that while I could ss_map mp_coop_doors_d as much as I wanted, merely renaming it to another bsp made it stop working (likely meaning at some point I deleted something that makes a map coop-capable, but Portal somehow remembered that map was 'blessed'), as did copy/pasting everything into a new map. So something really wonky is going on here.

At this point I've torn out all my hair. What's the bare minimum required to get a multiplayer map built/working?

Dewin wrote:
(likely meaning at some point I deleted something that makes a map coop-capable, but Portal somehow remembered that map was 'blessed')

This is not how computers work just FYI. There is no sorcery involved.

I'm guessing there is a worldspawn value set or something, but I have not touched Portal 2 mapping at all so I can't say for sure.

It turns out, the file name matters, and must start with mp_coop. (There must be some other way though, since the hack to play singleplayer maps in coop doesn't involve changing the filenames but instead uses the commentary system to add some extra entities).

So much for prefixing all my maps with dewin_ so I can separate them from the official ones!

Dewin wrote:
So much for prefixing all my maps with dewin_ so I can separate them from the official ones!

Name all your singleplayer maps dewin_ and all your multiplayer maps mp_coop_dewin_.

Edit: The map merely needs to contain mp_coop. ss_map foo_mp_coop_blah works.