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 type of oddball ardour tasks that’s damaged into Web consciousness. It’s a free recreation the place you play both an adventurer or a fortress filled 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 develop 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. 

Your complete recreation 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 an element time undertaking, 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 present engaged on a model with pixel graphics and a revamped UI that can be out there 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 under 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 utilize? 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 type of normal obeying manner, however form of a large number 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 take advantage of 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 try this myself in fact. I’m undecided if I’d use one thing like Unity or Unreal now if I had the selection since I don’t know methods to use both of them. However dealing with your personal engine can be an actual ache, particularly now that I’m doing one thing past textual content graphics. I take advantage of FMOD for sound. 

All of this has been fixed over the course of the undertaking, besides that SDL obtained launched a number of years in so we may do the ports. On the mechanical aspect of the sport, I don’t use quite a lot of exterior 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 undertaking for thus lengthy? Do you assume that is simpler to do by your self? That’s, since you wrote each line, is it simpler to keep up and alter?

A: It’s straightforward to overlook stuff! Trying to find ‘;’, which is a free 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 title my variables and objects persistently and memorably, and I go away sufficient comments round to remind myself of what’s occurring after I arrive at a spot of code. Typically it takes a number of searches to seek out the precise thread I’m attempting to tug on after 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 targeted solely on sure elements of the sport, so there’s type of an energetic molten core that I’ve a a lot better working information of. There are a number 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, definitely for me, who has no expertise engaged on a big multi-person undertaking, that is the way in which to go! Folks clearly get good at doing it the opposite manner, for instance over within the AAA video games context, and clearly a number of engineers are wanted over there to get issues achieved on time. I’d be hesitant to say I can go in and alter stuff sooner than they’ll, essentially, since I haven’t labored in that context earlier than, however it’s true that I don’t have any team-oriented or bureaucratic hurdles to leap by after I wish to make an alteration. I can simply go do it. However I additionally should do it alone.

Q: What’s the largest refactor/change that you simply needed to make?

A: There have been some refactors which have lasted for months, redoing sure information buildings and so forth, although I’m undecided something is ever a refactor strictly right here since there’s all the time alternatives to push the mechanics ahead concurrently and it is sensible 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 essentially the most mind-numbing factor I’ve most likely ever achieved. 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 in the end a mistake, however that was an enormous one. 

Q: Why was this was a mistake?

A: Once you declare a category that’s a type of merchandise, it locks you into that construction way more tightly than in case you simply have member parts. It’s good to have the ability to use digital capabilities and that type of factor, however the tradeoffs are simply an excessive amount of. I began utilizing a “instrument” merchandise within the hierarchy, which began to get numerous performance, and might now assist 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 recreation had been underneath that umbrella. 

We do quite a lot of procedural era, and if we needed to, say, generate an merchandise that acts partially like one factor and partially like one other, it’s simply manner tougher to try this when 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 totally different elements can simply be turned on and off, it’s simpler, and permits you to do extra. 

I believe some recreation builders discuss with this as an entity element system, although it’s my understanding that harder-core optimizer folks consider that as one thing else the place you’re really breaking issues down by particular person fields. Utilizing a single object with totally different allotted subobjects is nearly definitely worse for cache misses, which is a complete different factor, however the advantages in group, flexibility, and extensibility simply can’t be ignored, and the totally different subfields of the instrument merchandise aren’t used so usually that it turns into an optimization concern.

Q: Did you run into any points shifting from 32 bit to 64 bit? That appears like a type of issues that was big on the time however has develop into fairly accepted.

A: Under no circumstances! I’m struggling to think about a single concern. Thankfully for us, we already had our byte sizes underneath management fairly properly, because it comes up saving and loading the worlds; the format wanted to be nailed down again after we set that up, particularly as a result of we’ve needed to take care of 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 hassle. It simply ended up being actually good code for 64 bit conversion because of our different practices, solely by chance. The principle concern was simply getting the time collectively to make the change, after which it didn’t find yourself taking almost so long as I believed it will.

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

A: Yeah, the bottom algorithm is simply a part of it. We use A*, which is quick in fact, however it’s not ok by itself. We will’t benefit from among the improvements on that (e.g. jump point) since our map modifications a lot. Typically, folks have used approaches that add numerous bigger buildings on prime of the map to chop corners, and due to the altering map, these simply take too lengthy to keep up, or are in any other case a problem. So our strategy has been to only preserve observe of related elements reachable by strolling. These are fairly straightforward to replace even when the map modifications shortly, although it does contain some flood-filling. As an illustration, if water cuts the fortress in half, it must flood out from one aspect and replace a complete half of the fortress to a brand new index, however as soon as that’s achieved, it’s good, usually. Then that enables us to chop virtually all failed A* calls from the sport—our brokers simply want to question element numbers, and if the element numbers are the identical, they know the decision will succeed.

It’s quick to keep up, however the draw back is that the element indices are maintained for strolling solely. Which means flying creatures, as an illustration, don’t have international pathfinding intelligence that’s any totally different from a walker. In fight and some different conditions, we use short-range flood fills with their precise logic to offer them some benefits although. However it’s not ideally suited 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 exterior makes an attempt. In fact, it is likely to be doable with a very 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 simplest concept 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 keep up two indices directly, and one is unhealthy sufficient. Extra particular overlays can observe their pathing properties (and then you definately path by the overlays as an alternative of the tiles), however they’re arduous and sluggish to keep up because the map modifications. There are numerous different concepts floating round, like monitoring stairs, or performing some restricted path caching, and there are most likely some features to be made there. We’re definitely on the fringe of what we are able to at present assist when it comes to brokers and map complexity, so one thing’ll have to offer if we wish to get extra out of it.

Q: On that word, you’re simulating quite a lot of issues abruptly—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, apart from the graphical show itself. There’s quite a lot 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: Positive! The aspect undertaking 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 largely different video games, virtually all the time in different genres, however there are additionally a number of DF helper tasks, like the parable generator prototype. Nothing near seeing the sunshine of day, however it’s enjoyable to mess around.

Q: Along with your ~90 aspect tasks, have you ever explored every other programming languages? If that’s the 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 positive some issues would actually velocity up the belief of my designs although, so I ought to most likely not less than study some scripting and mess around with threading extra. Folks have even been type sufficient to produce some libraries and issues to assist on the market, however it’s simply troublesome to dam aspect undertaking day trip for tech studying when my aspect undertaking time is for enjoyable.

Q: You could have essentially the most fascinating launch notes. What’s your favourite bug and what brought on 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 number of movies made about it by this level. That was the one the place the cats had been exhibiting 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 after we spruced up venomous creatures.)

If you wish to strive Dwarf Fortress for your self, you’ll be able to download it from their website.

Tags: dwarf fortress, solo developer, video games

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