700,000 lines of code, 20 years, and one developer: How Dwarf Fortress is built

[Ed. note: While we take some time to rest up over the holidays and prepare for next year, we are re-publishing our top ten posts for the year. This is our number one post of 2021! Thanks for reading and we’ll see you in the new year. ]

Dwarf Fortress is a kind of oddball ardour tasks that’s damaged into Web consciousness. It’s a free sport the place you play both an adventurer or a fortress stuffed with dwarves in a randomly generated fantasy world. The simulation runs deep, with new video games creating a number of civilizations with histories, mythologies, and artifacts. 

It has turn into infamous, and rightly so. Particular person dwarves have emotional states, favourite gems, and grudges. And all of it takes place in an ASCII interface that appears imposing to newbies, however feels just like the textual content crawl in The Matrix: craftsdwarf, river, legendary megabeast. 

All the sport is product of 1 developer, Tarn Adams, aka Toady One, who has been engaged on Dwarf Fortress since 2002. For the primary 4 years it was a component time challenge, however since 2006 it’s been full time. He writes all of the code himself, though his brother helps out with design and creates tales based mostly on the sport. Up till now, he’s relied on donations to maintain him going, however he’s at the moment engaged on a model with pixel graphics and a revamped UI that will likely be accessible for buy on Steam. 

I reached out to Tarn Adams to see how he’s managed a single, rising codebase over 15+ years, the perils of pathing, and debugging useless cats. Our dialog beneath has been edited for readability. In order for you extra, we additionally spoke with Tarn on the podcast.


Q: What programming languages and different applied sciences do you employ? Mainly, what’s your stack? Has that modified over the 15-20 years you’ve been doing this?

A: DF is a few mixture of C and C++, not in some form of customary obeying means, however form of a multitude that’s accreted over time. I’ve been utilizing Microsoft Visible Studio since MSVC 6, although now I’m on some model of Visible Studio Group. 

I exploit OpenGL and SDL to deal with the engine issues. We went with these as a result of it was simpler to port them to OSX and Linux, although I nonetheless wasn’t in a position to do this myself after all. I’m undecided if I’d use one thing like Unity or Unreal now if I had the selection since I don’t know the right way to use both of them. However dealing with your personal engine can also be an actual ache, particularly now that I’m doing one thing past textual content graphics. I exploit FMOD for sound. 

All of this has been fixed over the course of the challenge, besides that SDL bought launched a couple of years in so we might do the ports. On the mechanical aspect of the sport, I don’t use plenty of outdoors libraries, however I’ve occasional picked up some random quantity gen stuff—I put in a Mersenne Twister an extended whereas in the past, and most lately I adopted SplitMix64, which was featured in a chat on the final Roguelike Celebration.

Q: What are the challenges in growing a single challenge for therefore lengthy? Do you assume that is simpler to do by your self? That’s, since you wrote each line, is it simpler to take care of and alter?

A: It’s straightforward to overlook stuff! Trying to find ‘;’, which is a unfastened technique however shut sufficient, we’re as much as 711,000 strains, so it’s simply not doable to maintain all of it in my head now. I attempt to identify my variables and objects constantly and memorably, and I depart sufficient comments round to remind myself of what’s occurring once I arrive at a spot of code. Typically it takes a number of searches to search out the precise thread I’m making an attempt to tug on once I go and revisit some piece of the sport I haven’t touched for a decade, which occurs fairly a bit. I’d say most modifications are centered solely on sure elements of the sport, so there may be form of an energetic molten core that I’ve a a lot better working information of. There are a couple of actually crusty bits that I haven’t checked out since earlier than the primary launch in 2006.

Concerning the relative ease of doing issues on my own, actually for me, who has no expertise engaged on a big multi-person challenge, that is the way in which to go! Individuals clearly get good at doing it the opposite means, for instance over within the AAA video games context, and clearly a number of engineers are wanted over there to get issues accomplished on time. I’d be hesitant to say I can go in and alter stuff sooner than they will, essentially, since I haven’t labored in that context earlier than, nevertheless it’s true that I don’t have any team-oriented or bureaucratic hurdles to leap by once I wish to make an alteration. I can simply go do it. However I additionally need to do it alone.

Q: What’s the most important refactor/change that you just needed to make?

A: There have been some refactors which have lasted for months, redoing sure knowledge buildings and so forth, although I’m undecided something is ever a refactor strictly right here since there’s at all times alternatives to push the mechanics ahead concurrently and it is smart to take action when the code information is recent. 

Including the Z coordinate to make the sport mechanically 3D (whereas nonetheless being textual content) was one other one, and actually probably the most mind-numbing factor I’ve most likely ever accomplished. Simply weeks and weeks and weeks of taking logic and performance calls that relied on X and Y and seeing how a Z suits in there.

Making the merchandise system polymorphic was finally a mistake, however that was a giant one. 

Q: Why was this was a mistake?

A: Once you declare a category that’s a form of merchandise, it locks you into that construction way more tightly than when you simply have member components. It’s good to have the ability to use digital features and that form of factor, however the tradeoffs are simply an excessive amount of. I began utilizing a “device” merchandise within the hierarchy, which began to get varied performance, and may now help something from a stepladder to a beehive to a mortar (and pestle, individually, ha ha), and it simply feels extra versatile, and I want each crafted merchandise within the sport had been beneath that umbrella. 

We do plenty of procedural technology, and if we wished to, say, generate an merchandise that acts partially like one factor and partially like one other, it’s simply means tougher to do this if you find yourself locked down in a category hierarchy. Including issues like diamond dependencies and all that simply find yourself tying you in knots when there are cleaner methods to do it. If completely different parts can simply be turned on and off, it’s simpler, and permits you to do extra. 

I feel some sport builders consult with this as an entity part system, although it’s my understanding that harder-core optimizer individuals consider that as one thing else the place you’re truly breaking issues down by particular person fields. Utilizing a single object with completely different allotted subobjects is nearly actually worse for cache misses, which is an entire different factor, however the advantages in group, flexibility, and extensibility simply can’t be ignored, and the completely different subfields of the device merchandise aren’t used so usually that it turns into an optimization difficulty.

Q: Did you run into any points transferring from 32 bit to 64 bit? That looks like a kind of issues that was large on the time however has turn into fairly accepted.

A: Under no circumstances! I’m struggling to consider a single difficulty. Thankfully for us, we already had our byte sizes beneath management fairly nicely, because it comes up saving and loading the worlds; the format wanted to be nailed down again once we set that up, particularly as a result of we’ve needed to cope with endian stuff between OSes and all that. And we don’t do any gnarly pointer operations or different stuff that may have gotten us in bother. It simply ended up being actually good code for 64 bit conversion on account of our different practices, totally accidentally. The primary difficulty was simply getting the time collectively to make the change, after which it didn’t find yourself taking practically so long as I believed it might.

Q: I’ve seen different video games just like DF die on their pathfinding algorithms.What do you employ and the way do you retain it environment friendly?

A: Yeah, the bottom algorithm is barely a part of it. We use A*, which is quick after all, nevertheless it’s not adequate by itself. We are able to’t make the most of among the improvements on that (e.g. jump point) since our map modifications a lot. Typically, individuals have used approaches that add varied bigger buildings on high of the map to chop corners, and due to the altering map, these simply take too lengthy to take care of, or are in any other case a trouble. So our method has been to only maintain observe of linked parts reachable by strolling. These are fairly straightforward to replace even when the map modifications rapidly, although it does contain some flood-filling. For example, if water cuts the fortress in half, it must flood out from one aspect and replace an entire half of the fortress to a brand new index, however as soon as that’s accomplished, it’s good, usually. Then that permits us to chop virtually all failed A* calls from the sport—our brokers simply want to question part numbers, and if the part numbers are the identical, they know the decision will succeed.

It’s quick to take care of, however the draw back is that the part indices are maintained for strolling solely. Because of this flying creatures, as an illustration, don’t have international pathfinding intelligence that’s any completely different from a walker. In fight and some different conditions, we use short-range flood fills with their precise logic to present them some benefits although. Nevertheless it’s not ultimate for them.

I’m undecided we’ll try different buildings right here to make it work any higher. For our map sizes, they’ve all failed, together with some outdoors makes an attempt. In fact, it could be doable with a extremely concerted effort, and I’ve seen different video games which have managed, as an illustration, some rectangular overlays and so forth that appear promising, however I’m undecided how unstable or giant their maps had been. 

The most straightforward thought would simply be one thing like including a brand new index for fliers, however that’s a big reminiscence and velocity hit, since we’d want to take care of two indices without delay, and one is unhealthy sufficient. Extra particular overlays can observe their pathing properties (and then you definately path by the overlays as a substitute of the tiles), however they’re laborious and sluggish to take care of because the map modifications. There are numerous different concepts floating round, like monitoring stairs, or doing a little restricted path caching, and there are most likely some beneficial properties to be made there. We’re actually on the fringe of what we are able to at the moment help when it comes to brokers and map complexity, so one thing’ll have to present if we wish to get extra out of it.

Q: On that word, you’re simulating plenty of issues suddenly—how do you handle so many so many actors asynchronously (or do you)?

A: If we’re speaking about asynchronous as in multithreading, then no, we don’t do any of that, other than the graphical show itself. There’s plenty of promise right here, even with microthreading, which the neighborhood has helped me out with, however I haven’t had time to dive into. I don’t have any expertise and it’s a bug-prone factor.

Q: Have you ever tried different tasks/applied sciences alongside DF?

A: Certain! The aspect challenge folder that’s migrated between computer systems for the final ten years or so has about 90 tasks in it. A few of them lasted for days, some for a number of years. They’re principally different video games, virtually at all times in different genres, however there are additionally a couple of DF helper tasks, like the parable generator prototype. Nothing near seeing the sunshine of day, nevertheless it’s enjoyable to mess around.

Q: Together with your ~90 aspect tasks, have you ever explored some other programming languages? In that case, any favorites?

A: Ha ha, nope! I’m extra of a noodler over on the design aspect, slightly than with the tech. I’m certain some issues would actually velocity up the conclusion of my designs although, so I ought to most likely not less than study some scripting and mess around with threading extra. Individuals have even been type sufficient to provide some libraries and issues to assist on the market, nevertheless it’s simply troublesome to dam aspect challenge trip for tech studying when my aspect challenge time is for stress-free.

Q: You’ve gotten probably the most fascinating launch notes. What’s your favourite bug and what prompted it?

A: It’s most likely boring for me to say, however I simply can’t beat the drunken cat bug. There’ve been a couple of movies made about it by this level. That was the one the place the cats had been displaying up useless all around the tavern flooring, and it turned out they had been ingesting spilled alcohol once they cleaned their paws. One quantity was off within the ingest-while-cleaning code, and it despatched them by all of the signs of alcohol poisoning (which we added once we spruced up venomous creatures.)

If you wish to attempt Dwarf Fortress for your self, you may download it from their website.

Tags: dwarf fortress, solo developer, video games

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