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 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. 

The whole 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 presently engaged on a model with pixel graphics and a revamped UI that might 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 lifeless 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? 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 commonplace obeying approach, 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 Neighborhood. 

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 try 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 best way 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 exploit FMOD for sound. 

All of this has been fixed over the course of the undertaking, besides that SDL bought launched just a few years in so we may do the ports. On the mechanical facet of the sport, I don’t use a whole lot 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 undertaking for thus lengthy? Do you suppose 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 neglect stuff! Looking for ‘;’, which is a free technique however shut sufficient, we’re as much as 711,000 traces, so it’s simply not attainable to maintain all of it in my head now. I attempt to title 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. Generally it takes a number of searches to search 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 centered solely on sure elements of the sport, so there’s type of an lively molten core that I’ve a a lot 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, actually for me, who has no expertise engaged on a big multi-person undertaking, 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 accomplished 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 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 simply needed to make?

A: There have been some refactors which have lasted for months, redoing sure knowledge constructions 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 data is contemporary. 

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 in the end a mistake, however that was a giant 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 in the event you simply have member components. It’s good to have the ability to use digital features 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 varied 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 have been below that umbrella. 

We do a whole 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 approach more durable 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 parts can simply be turned on and off, it’s simpler, and permits you to do extra. 

I feel some recreation builders confer 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 really breaking issues down by particular person fields. Utilizing a single object with totally 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 totally different subfields of the instrument merchandise aren’t used so usually that it turns into an optimization subject.

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

A: In no way! I’m struggling to consider a single subject. Thankfully for us, we already had our byte sizes below management fairly effectively, 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 cope with 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 as a result of our different practices, fully by chance. The primary subject 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 much 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 after all, but it surely’s not adequate by itself. We will’t reap the benefits 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 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 parts 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 facet and replace an entire half of the fortress to a brand new index, however as soon as that’s accomplished, 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, for 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 present them some benefits although. But it surely’s not best for them.

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

The simplest concept would simply be one thing like including a brand new index for fliers, however that’s a big reminiscence and pace hit, since we’d want to keep up two indices directly, and one is dangerous sufficient. Extra particular overlays can monitor their pathing properties (and then you definitely path by the overlays as an alternative of the tiles), however they’re arduous and gradual to keep up 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 positive aspects to be made there. We’re actually on the fringe of what we are able to presently assist 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 notice, you’re simulating a whole lot of issues all of sudden—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, except for the graphical show itself. There’s a whole lot 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 tasks/applied sciences alongside DF?

A: Positive! The facet 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 principally different video games, nearly all the time in different genres, however there are additionally just a few DF helper tasks, like the parable generator prototype. Nothing near seeing the sunshine of day, but it surely’s enjoyable to mess around.

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

A: Ha ha, nope! I’m extra of a noodler over on the design facet, somewhat than with the tech. I’m positive some issues would actually pace up the belief of my designs although, so I ought to most likely at the least be taught some scripting and mess around with threading extra. Individuals have even been type sufficient to produce some libraries and issues to assist on the market, but it surely’s simply tough to dam facet undertaking outing for tech studying when my facet undertaking time is for enjoyable.

Q: You’ve got probably the most attention-grabbing launch notes. What’s your favourite bug and what triggered it?

A: It’s most likely 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 have been exhibiting up lifeless everywhere in the tavern ground, and it turned out they have 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 attempt Dwarf Fortress for your self, you may download it from their website.

Tags: dwarf fortress, solo developer, video games

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