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 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 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 a component 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 based mostly on the sport. Up till now, he’s relied on donations to maintain him going, however he’s at the moment 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 beneath 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 employ? 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 form of normal obeying approach, however kind 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 ready 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 find out how to use both of them. However dealing with your individual 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 venture, besides that SDL obtained launched a couple of years in so we might do the ports. On the mechanical aspect of the sport, I don’t use numerous outdoors 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 venture 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 simple to overlook stuff! Looking for ‘;’, which is a free methodology 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. Typically it takes a number of searches to seek out the precise thread I’m making an attempt 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 may be form of an energetic molten core that I’ve a a lot better working data of. There are a couple 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 venture, that is the way in which to go! Folks 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 carried out 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, nevertheless it’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 must 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 knowledge 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 data 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 in all probability 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 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 form of merchandise, it locks you into that construction way more tightly than when you simply have member components. It’s good to have the ability to use digital capabilities and that form of factor, however the tradeoffs are simply an excessive amount of. I began utilizing a “device” merchandise within the hierarchy, which began to get varied 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 have been beneath that umbrella. 

We do numerous procedural technology, and if we wished 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 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 means that you can do extra. 

I believe some recreation builders consult 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 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 usually that it turns into an optimization concern.

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

A: By no means! I’m struggling to think about a single concern. Thankfully for us, we already had our byte sizes beneath management fairly effectively, because it comes up saving and loading the worlds; the format wanted to be nailed down again once 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 bother. It simply ended up being actually good code for 64 bit conversion because of our different practices, completely 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 assumed it might.

Q: I’ve seen different video games just like DF die on their pathfinding algorithms.What do you employ 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 after all, nevertheless it’s not ok by itself. We are able to’t reap the benefits of a few of the improvements on that (e.g. jump point) since our map adjustments a lot. Usually, individuals have used approaches that add varied 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 trouble. So our method has been to simply maintain observe of linked parts reachable by strolling. These are fairly simple to replace even when the map adjustments rapidly, 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 carried out, 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 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. Nevertheless it’s not supreme 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 could be doable 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 most straightforward thought 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 without delay, and one is unhealthy sufficient. Extra particular overlays can observe their pathing properties (and then you definitely path by way of the overlays as a substitute of the tiles), however they’re onerous and sluggish to keep up because the map adjustments. There are numerous different concepts floating round, like monitoring stairs, or doing a little restricted path caching, and there are in all probability some positive factors to be made there. We’re definitely on the fringe of what we are able to at the moment 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 be aware, you’re simulating numerous issues —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 numerous 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 aspect 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 largely different video games, nearly all the time in different genres, however there are additionally a couple of DF helper tasks, like the parable generator prototype. Nothing near seeing the sunshine of day, nevertheless 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, moderately than with the tech. I’m positive some issues would actually velocity up the conclusion of my designs although, so I ought to in all probability no 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, nevertheless it’s simply troublesome to dam aspect venture day trip for tech studying when my aspect venture time is for enjoyable.

Q: You will have essentially the most fascinating 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 a couple of movies made about it by this level. That was the one the place the cats have been exhibiting up lifeless all around 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 way of all of the signs of alcohol poisoning (which we added once 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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