Is it possible to start a map with a text crawl in vanilla or boom compatible port?

Not to my knowledge.  I think the text crawls are hard-coded to appear at the end of the usual maps (E1-4M8, MAP06, MAP11, etc.), but that there's no way to have them appear before or inside maps without some intense source code modification or whatever.

You could always do what The Sky May Be did (yes, I am absolutely cribbing mapping ideas from The Sky May Be) and have a sign with a scrolling texture containing an introductory text crawl in the map itself, on some kind of "mission computer" or something.  It might feel a little hacky but it's an idea.

In Rowdy Rudy, I made a fake little "text crawl" map you can find in map slot 11 - https://www.doomworld.com/idgames/levels/doom2/p-r/rwdyrudy

Basically it's a black room that uses several doors with mid textures applied, and the font is written on the textures. (Take a look in Doom Builder and in Slade to see how it's all put together). When you walk forward, the sequence of doors open, taking the middle textures with the text on them up into the air.

It's complicated as all hell, but you could use this approach in combination with a timed "romero head" being crushed in an external sector to force the map to end shortly after the hacky text crawl finishes.

The end result actually looked pretty good in Rowdy Rudy (imo) and it's essentially either this, or something like what StupidBunny mentioned - there's no other way in vanilla... In Boom, the mapping trick to have scrolling text could be a bit easier to implement, but it's still not as "legit" as a regular text crawl.

1 hour ago, HrnekBezucha said:

I'd love to start my map with the story text crawl as a mission briefing. I know it's possible with stuff like UMAPINFO but that's not compatible with the ports I have and target meaning either chocolate/crispy or pr-boom+

I know that is not the answer you are looking for. But if you are only targeting your map for only one of the ports (and not all 3 of them) that you mentioned, then you can replace PrBoom+ and give DSDA-Doom source port a try (it is a fork of PrBoom+ and thus has pretty much the same feel). DSDA supports umapinfo and as many more QoL feature over PrBoom+.

9 hours ago, HrnekBezucha said:

gzdoom but something tells me to stick with vanilla, and learn it well before moving onto more advanced stuff. Ambition needs to be matched with skill. 

If I can provide a different perspective - there's nothing wrong with starting in Vanilla format to get a feel for mapping before trying out stuff like Boom format or UDMF (it's pretty much what I did after all), but once you're familiar with the basics there's no need to stay mapping in Vanilla. The more advanced stuff in Vanilla doesn't translate well to UDMF (for example, making over/under bridges in Vanilla is rather finnicky, while UDMF allows you to simply make a 3D floor without any fuss or muss), so your time spent mapping in Vanilla format will give diminishing returns. There's also a whole host of things supported in UDMF that simply don't exist in Vanilla (like ACS and DECORATE), so if you want to learn how to use them, your time would be better spent getting into the nitty-gritty with them instead of vanilla mapping.

I would recommend you try moving on to UDMF if you're interested in making stuff for GZDoom. You don't have to jump off the deep end and try complex stuff immediately, but you should definitely figure out how to set up the simple stuff like doors, lifts, switches, etc. and then try out new stuff from there.

To expand on what SMG_Man is saying, you should map in whatever format matches up best with whatever port you use (and whatever port you want others to use). Vanilla maps can be played in all ports, where as UDMF maps can only work in advanced ports - but I'd say at least 70-80% of people use a UDMF-compat port these days, and just as was already stated UDMF has a lot more options and is probably easier overall. There's a billion and one confusing and arbitrary limits and oddities when catering to vanilla that you don't need to worry about in UDMF.

56 minutes ago, HrnekBezucha said:

Can you guys suggest a wad that's udmf and uses a bunch of its new mechanics? For inspiration

Well, if you'll let me shill my work for a second, I have a megawad that I've been working on for the past several months that's built in UDMF:

It requires GZDoom as mentioned in the title, and while I do favor more vanilla-style design for the level layouts, it won't take you long to see things going on that just aren't possible in vanilla Doom. There are also a bunch of new weapons, monsters, and powerups as well.

@Stupid Bunny now you mention it, I remember scrolling text texture in the first map of Icarus. Vanilla doom only knows to scroll left to right, which is totally fine with short text but not for whole sentences. On the other hand, I'm pretty sure boom can scroll bottom up, which would be perfect. Having a computer screen with it, or smt. I like that. 

And I need to check out The Sky May Be, seems kinda wild from the screenshots. 

@Doomkid I've heard Rowdy Rudy has a bunch of cool ideas implemented. Like giving the player a starting weapon that isn't useless. Definitely gonna check it out soon. 

Having doors with the text on them is super hacky but that's exactly the thing I love. Constrains breed creativity! One day I'd love to understand the black magic within Eternal Doom.. That's just crazy

@ReaperAA I'm seriously considering getting Woof or even gzdoom but something tells me to stick with vanilla, and learn it well before moving onto more advanced stuff. Ambition needs to be matched with skill. 

Thanks for answers, everybody! 

@SMG_Man @Doomkid Yeah, I can see what you're saying. Too bad UDMF isn't too widely supported. I'm mapping on Linux with Eureka at the moment, so I'd need to learn mapping in SLADE. I mean, it's probably just a matter of time before I make the leap because I don't want to stay with vanilla forever. What I'm worried about is having too many options and possibilities. The empty canvas problem. Can you guys suggest a wad that's udmf and uses a bunch of its new mechanics? For inspiration

@SMG_Man WOW! Yeah, now this is cool, I'm having a blast. The maps are way more fun with all these new mechanics. Okay, I'm learning slade udmf