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 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 grow 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. 

The whole 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 venture, 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 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 lifeless cats. Our dialog under has been edited for readability. If you’d like 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 normal obeying method, however kind 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 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 learn how 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 venture, besides that SDL acquired launched just a few years in so we might do the ports. On the mechanical facet of the sport, I don’t use loads 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 just lately I adopted SplitMix64, which was featured in a chat on the final Roguelike Celebration.

Q: What are the challenges in creating a single venture 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 keep up and alter?

A: It’s straightforward to neglect stuff! Trying to find ‘;’, which is a free methodology however shut sufficient, we’re as much as 711,000 strains, so it’s simply not potential 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 happening after 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 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 components of the sport, so there may be type of an lively molten core that I’ve a significantly better working information of. There are just a few 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 venture, that is the way in which to go! Individuals clearly get good at doing it the opposite method, 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 via after 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 all the time alternatives to push the mechanics ahead concurrently and it is smart to take action when the code information 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 matches 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 type of merchandise, it locks you into that construction way more tightly than in case 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 “software” merchandise within the hierarchy, which began to get numerous performance, and might 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 have been beneath that umbrella. 

We do loads 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 method tougher to try this if you end up 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 believe some sport builders confer with this as an entity part 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 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 software merchandise aren’t used so typically 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 kind of issues that was enormous on the time however has grow to be fairly accepted.

A: In no way! I’m struggling to think about a single concern. Thankfully for us, we already had our byte sizes beneath 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 which may have gotten us in bother. It simply ended up being actually good code for 64 bit conversion resulting from our different practices, solely accidentally. The principle concern 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 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 barely a part of it. We use A*, which is quick in fact, nevertheless it’s not ok by itself. We are able to’t benefit from a number of the improvements on that (e.g. jump point) since our map modifications a lot. Typically, folks 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 trouble. So our strategy has been to only 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. As an illustration, if water cuts the fortress in half, it must flood out from one facet and replace a complete half of the fortress to a brand new index, however as soon as that’s accomplished, it’s good, typically. 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 keep up, however the draw back is that the part indices are maintained for strolling solely. Which means that flying creatures, as an illustration, don’t have world 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 excellent 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 could be potential 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 unsure how unstable or massive 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 you then path via the overlays as a substitute of the tiles), however they’re exhausting and sluggish 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 factors to be made there. We’re definitely on the fringe of what we are able to at present help by way of 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 loads of issues unexpectedly—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 loads 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: Certain! The facet venture 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 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, nevertheless it’s enjoyable to mess around.

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

A: Ha ha, nope! I’m extra of a noodler over on the design facet, fairly 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 a minimum of study some scripting and mess around with threading extra. Individuals have even been form sufficient to produce some libraries and issues to assist on the market, nevertheless it’s simply troublesome to dam facet venture trip for tech studying when my facet venture time is for stress-free.

Q: You have got 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 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 flooring, and it turned out they have been ingesting spilled alcohol after 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’ll be able to download it from their website.

Tags: dwarf fortress, solo developer, video games

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