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 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 change 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 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 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 shall 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 beneath has been edited for readability. If you would 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 sort of customary 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 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 how one can 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 received launched just a few years in so we might 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 creating 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 take care of and alter?

A: It’s simple to overlook stuff! Trying to find ‘;’, which is a unfastened methodology however shut sufficient, we’re as much as 711,000 traces, 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 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 adjustments are centered solely on sure components of the sport, so there’s sort of an lively molten core that I’ve a a lot 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, actually for me, who has no expertise engaged on a big multi-person undertaking, that is the best way 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 carried out on time. I’d be hesitant to say I can go in and alter stuff quicker than they will, 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 way of once I need 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 just 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 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 most likely ever carried out. 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 an enormous one. 

Q: Why was this was a mistake?

A: If you declare a category that’s a sort of merchandise, it locks you into that construction far more tightly than in case you simply have member components. It’s good to have the ability to use digital features and that sort 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 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 recreation had been underneath that umbrella. 

We do a whole lot 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 manner 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 elements can simply be turned on and off, it’s simpler, and means that you can do extra. 

I believe some recreation builders discuss 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 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 typically that it turns into an optimization concern.

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

A: By no means! I’m struggling to consider a single concern. Luckily for us, we already had our byte sizes underneath 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 resulting from our different practices, completely accidentally. The primary concern was simply getting the time collectively to make the change, after which it didn’t find yourself taking practically so long as I assumed 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 after all, but it surely’s not adequate by itself. We are able to’t reap the benefits of a number of the improvements on that (e.g. jump point) since our map adjustments a lot. Typically, individuals have used approaches that add numerous 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 simply preserve observe of linked elements reachable by strolling. These are fairly simple to replace even when the map adjustments shortly, although it does contain some flood-filling. As an example, 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 carried out, it’s good, usually. 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 take care of, however the draw back is that the part indices are maintained for strolling solely. Which means that flying creatures, for example, 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 perfect 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. After all, it may be doable with a very 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 massive their maps had been. 

The most straightforward 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 take care of two indices directly, and one is dangerous sufficient. Extra particular overlays can observe their pathing properties (and then you definitely path by way of the overlays as an alternative of the tiles), however they’re exhausting and gradual to take care of because the map adjustments. 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 actually 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 observe, you’re simulating a whole lot 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, 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: Certain! 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: Along with your ~90 facet tasks, 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 facet, relatively than with the tech. I’m certain some issues would actually pace up the belief of my designs although, so I ought to most likely at the very least study some scripting and mess around with threading extra. Folks have even been sort sufficient to produce some libraries and issues to assist on the market, but it surely’s simply troublesome to dam facet undertaking outing for tech studying when my facet undertaking time is for enjoyable.

Q: You’ve got essentially 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 had been exhibiting up useless everywhere in the tavern flooring, and it turned out they had been ingesting spilled alcohol after they cleaned their paws. One quantity was off within the ingest-while-cleaning code, and it despatched them by way of 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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