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 initiatives 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 out to be 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 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 an element time mission, 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 primarily based 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 might be obtainable 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. If you need extra, we additionally spoke with Tarn on the podcast.


Q: What programming languages and different applied sciences do you utilize? Principally, 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 commonplace obeying approach, however type 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 ready to try this myself in fact. I’m unsure if I’d use one thing like Unity or Unreal now if I had the selection since I don’t know the best 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 take advantage of FMOD for sound. 

All of this has been fixed over the course of the mission, besides that SDL obtained launched just a few years in so we may do the ports. On the mechanical aspect of the sport, I don’t use a variety of exterior libraries, however I’ve occasional picked up some random quantity gen stuff—I put in a Mersenne Twister a protracted whereas in the past, and most not too long ago I adopted SplitMix64, which was featured in a chat on the final Roguelike Celebration.

Q: What are the challenges in creating a single mission 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! Looking for ‘;’, 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 identify my variables and objects persistently and memorably, and I depart sufficient comments round to remind myself of what’s happening once I arrive at a spot of code. Generally it takes a number of searches to seek out the precise thread I’m attempting 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 targeted solely on sure components of the sport, so there’s type of an lively molten core that I’ve a significantly better working data of. There are just a few actually crusty bits that I haven’t checked out since earlier than the primary launch in 2006.

Relating to the relative ease of doing issues on my own, definitely for me, who has no expertise engaged on a big multi-person mission, that is the best way to go! Individuals clearly get good at doing it the opposite approach, for instance over within the AAA video games context, and clearly a number of engineers are wanted over there to get issues executed on time. I’d be hesitant to say I can go in and alter stuff quicker than they’ll, essentially, since I haven’t labored in that context earlier than, but it surely’s true that I don’t have any team-oriented or bureaucratic hurdles to leap via once I need to make an alteration. I can simply go do it. However I additionally should 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 information constructions and so forth, although I’m unsure something is ever a refactor strictly right here since there’s at all times alternatives to push the mechanics ahead concurrently and it is sensible to take action when the code data is contemporary. 

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 in all probability ever executed. Simply weeks and weeks and weeks of taking logic and performance calls that relied on X and Y and seeing how a Z matches 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: If you declare a category that’s a type of merchandise, it locks you into that construction far more tightly than when 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 “device” 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 sport had been below that umbrella. 

We do a variety of procedural technology, and if we needed to, say, generate an merchandise that acts partially like one factor and partially like one other, it’s simply approach tougher to try this when you’re 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 lets you do extra. 

I feel some sport builders seek advice from 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 totally different allotted subobjects is sort of 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 device merchandise aren’t used so typically that it turns into an optimization subject.

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

A: Under no circumstances! I’m struggling to consider a single subject. Luckily for us, we already had our byte sizes below management fairly nicely, 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 which may have gotten us in hassle. It simply ended up being actually good code for 64 bit conversion attributable to our different practices, fully accidentally. The principle subject was simply getting the time collectively to make the change, after which it didn’t find yourself taking almost so long as I assumed it could.

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 just a part of it. We use A*, which is quick in fact, but it surely’s not adequate by itself. We will’t benefit from among the improvements on that (e.g. jump point) since our map modifications a lot. Usually, individuals have used approaches that add numerous bigger constructions 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 simply preserve monitor 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. For example, 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 executed, it’s good, typically. Then that enables us to chop nearly 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 keep up, however the draw back is that the part indices are maintained for strolling solely. Which means that flying creatures, as an example, 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 preferrred for them.

I’m unsure we’ll try different constructions 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 may be doable with a extremely concerted effort, and I’ve seen different video games which have managed, as an example, some rectangular overlays and so forth that appear promising, however I’m unsure how risky 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 monitor their pathing properties (and then you definitely path via 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 in all probability some good points 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 need to get extra out of it.

Q: On that notice, you’re simulating a variety 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 a variety of promise right here, even with microthreading, which the group 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 initiatives/applied sciences alongside DF?

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

Q: Along with your ~90 aspect initiatives, have you ever explored another 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 certain some issues would actually velocity up the conclusion of my designs although, so I ought to in all probability at the least be taught some scripting and mess around with threading extra. Individuals have even been sort sufficient to produce some libraries and issues to assist on the market, but it surely’s simply troublesome to dam aspect mission outing for tech studying when my aspect mission time is for enjoyable.

Q: You could have essentially the most attention-grabbing launch notes. What’s your favourite bug and what brought about it?

A: It’s in all probability boring for me to say, however I simply can’t beat the drunken cat bug. There’ve been just a few movies made about it by this level. That was the one the place the cats had been displaying up useless everywhere in 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 via 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 may download it from their website.

Tags: dwarf fortress, solo developer, video games

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