Procedurally generating structures with rooms / corridors / stairs / doors

I think its a fart to say there is no place in games for procedural generation, but I will also concede that the type of generation you are describing here is very time consuming to build. You've got the right idea with modules and what not.

A simple approach, which is re-usable for 3D, would be to place one module, and then have a function go a single room at a time randomly choosing another module next to the first that has matching connections. WFC is an algorithm that is used to match connections, but you can make up whatever logic you want for this, and it could be as simple as saying module with north door flag must be next to module with south door flag. Then you could have a set of modules that are "end walls" and when the max distance from the original module is reached you choose from only dead end rooms to cap off the space. Those older games you mention are doing this in 2D, but in each 2D array position they are placing a 3D room model. For some newer games, you can see that Alien Isolation is doing this with a 3D array, and The Bunker(by Frictional Games) is doing the same thing but with a 2D array.

When I built a procedural voxel thing, I built it on a single 2D layer first so that the logic was easier to work out, and then just switched all my arrays to 3D multidimensional/nested arrays and expanded the logic to additionally check from up and down directions. Like start simply by making a 2D generator and then layer your 2D generator on top of itself like a cake.

As for the off-size tile issue you mention in your last post, its good to keep in mind that the placement of your premade rooms does not actually have to correspond to the first array. The array you are generating can tell you what modules are next to each other but does not have to refer to global positions, that can be its own logic. This is hard to explain, here is a video with a variety of resources that might get you thinking about that.

Unrelated, Deep Rock Galactic devs posted a really cool dev log where they do procedural work here. They spawn a bunch of pre-made rooms in a sphere, and then they draw a line between connections and generate a cylinder shape around the line to be a hallway. Then they apply noise patterns to blend the meshes together into caves. Neat

Anyway this is a hole that you can fall down forever.

xyz procedural generation is a tool like many others, it has its uses.
it can be used to create unique never before seen maps like in minecraft and spelunking and civilization and diablo and
but if it is not done right it can lead to bad maps. this is not a procedural generation problem, it's a bad/insufficient code problem.

MirceaKitsune I think it can be a good idea when done right.

but you are not going to do it right the first time. go and learn algorithms, do something simple, create a 2D map.
I'm using procedural generation, but before getting to this I made dozens of perlin generators and other things, it's not something you just go and do on the first try. so stop planning and start trying, you are a newbie.

MirceaKitsune Procedural generation is the main reason Minecraft was such a big thing

minecraft was ALL procedural generation, the guy worked on it for years and read books. you don't get to just go and do it with a 30 second search and a youtube tutorial.

MirceaKitsune Finding the right assets has been a tad harder

how about you make your own assets? what are you contributing to your project? you want the code done and the art done and just to assemble it like LEGOs AND for it to be perfect.

MirceaKitsune prototype CSG with an unique texture atlas should do

forget about CSG. or don't, ignore all the advice from more experienced people, make your mistakes.
but please learn from them.

MirceaKitsune Also tiles of different sizes, you want a fixed grid size unless you want a new layer of complexity filling multiple cells and requesting different neighbors per tile.

you can do same size tiles and still get a good map, just make the tiles more complex. a tile can have a little maze and still connect 4 ways. add doors inside, traps, obstacles.
when you randomize it all the tiles will still be valid, then add a start and end, and then you generate the scenes for the maze.
which is what I told you: an algorithms side, a data side and a generation side.
you can do SCG all you want, but if your algorithm is bad the map will be bad, and if there's no data you can't check if the map is good at runtime, and your players will run into walls.

CakeCadaver Unrelated, Deep Rock Galactic devs posted a really cool dev log where they do procedural work here. They spawn a bunch of pre-made rooms in a sphere, and then they draw a line between connections and generate a cylinder shape around the line to be a hallway. Then they apply noise patterns to blend the meshes together into caves. Neat

that is neat

xyz I've never seen a Minecraft map that I've never seen before. They all look the same to me.

it doesn't have to do so much with what they look like but how they play.
from a mechanical standpoint each game of minecraft can be different because the order in which the resources can be acquired and the enemies that are fought are different, so to the average player it feels like a different adventure with unique moments.
this is what a game is.

xyz They're just endless spatial permutations of the exact same stuff.

so is the universe

xyz If you've seen one map, no map you see afterwards can surprise you anymore.

not really, one map you find lava on the surface, in another you find a village very close by, in another there's a ravine, in another, an ocean.
maybe you are thinking of starfield/no mans sky where there's absolutely nothing on the endless planets, but minecraft has plenty of content.
yes the content can run out, but that's true of any game.

and what makes these worlds work is the exploration part, that primal part of our brains that enjoys experiencing new things, being in a completely new environment and trying to memory it.

xyz If you enjoy tinkering with pg, knock yourself out, do it 24/7. However, from project management standpoint, using this "tool" only makes sense if it'll save time/money.

it does save time. a game with procedural generation takes away the need to manually build the levels. these can still be designed, procedural isn't always random. for example in diablo 2 there's always going to be teleporters in the same areas.

xyz For a one-man-band, developing and balancing a pg system is often much more work than just building "fixed" content while the final impact on the player experience may be exactly the same and often worse with pg.

depends on the game, if procedural generation is a core area of the game, it is essential to have it. but for something like a metroidvania it would often be better to have an actual designed level.
look at 2 games that fail at replayability: subnautica and planet crafter. they use manually constructed levels, this helps with telling a story but the game can only be player once, which is a problem for planet crafter.

xyz Especially if you raise their expectations by touting how "unique" each generated level is.

you ARE thinking of no mans sky and starfield

MirceaKitsune I want to generate entire 3D levels procedurally based on a random seed or noise, namely buildings with rooms and corridors whether scifi facilities or medieval dungeons.

Are you specifically interested in PG or just want variety in the cards? You could try replacing Artificial Intelligence with Natural Intelligence. Allow players to create their own maps by releasing the appropriate tools. It would also increase the appeal of the game.