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 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 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. 

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 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 presently engaged on a model with pixel graphics and a revamped UI that will probably 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 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 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 type of normal obeying manner, 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 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 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 undertaking, besides that SDL acquired launched a couple of years in so we may do the ports. On the mechanical facet of the sport, I don’t use quite a lot 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 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 simple to neglect stuff! Looking for ‘;’, which is a unfastened methodology however shut sufficient, we’re as much as 711,000 traces, 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 go away sufficient comments round to remind myself of what’s happening after 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 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 centered solely on sure components of the sport, so there’s type of an energetic molten core that I’ve a a lot better working information of. There are a couple of 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 way in which to go! Individuals 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 completed 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, however it’s true that I don’t have any team-oriented or bureaucratic hurdles to leap by way of after I wish 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 simply needed to make?

A: There have been some refactors which have lasted for months, redoing sure information buildings 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 sensible to take action when the code information is recent. 

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 completed. 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: 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 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 may 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 below that umbrella. 

We do quite a lot of procedural era, and if we wished to, say, generate an merchandise that acts partially like one factor and partially like one other, it’s simply manner 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 completely different elements can simply be turned on and off, it’s simpler, and means that you can do extra. 

I feel some sport builders check with this as an entity element system, although it’s my understanding that harder-core optimizer folks consider that as one thing else the place you’re truly breaking issues down by particular person fields. Utilizing a single object with completely different allotted subobjects is sort of 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 completely different subfields of the device merchandise aren’t used so usually that it turns into an optimization challenge.

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 change into fairly accepted.

A: By no means! I’m struggling to consider a single challenge. Luckily for us, we already had our byte sizes below 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 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 as a result of our different practices, completely accidentally. The principle challenge 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 barely a part of it. We use A*, which is quick in fact, however it’s not adequate by itself. We will’t reap the benefits of 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 buildings on high 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 only hold monitor of related elements reachable by strolling. These are fairly simple to replace even when the map modifications rapidly, 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 an entire half of the fortress to a brand new index, however as soon as that’s completed, it’s good, usually. Then that enables us to chop virtually all failed A* calls from the sport—our brokers simply want to question element numbers, and if the element numbers are the identical, they know the decision will succeed.

It’s quick to keep up, however the draw back is that the element indices are maintained for strolling solely. Which means flying creatures, for example, don’t have world pathfinding intelligence that’s any completely 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 superb for them.

I’m unsure we’ll try different buildings 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 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 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 without delay, and one is unhealthy sufficient. Extra particular overlays can monitor their pathing properties (and you then path by way of the overlays as an alternative of the tiles), however they’re laborious 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 most likely some positive factors to be made there. We’re actually on the fringe of what we will presently help when it comes to brokers and map complexity, so one thing’ll have to offer if we wish to get extra out of it.

Q: On that observe, you’re simulating quite a lot of issues abruptly—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 quite a lot of promise right here, even with microthreading, which the neighborhood 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 facet undertaking 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, virtually all the time in different genres, however there are additionally a couple of DF helper initiatives, like the parable generator prototype. Nothing near seeing the sunshine of day, however it’s enjoyable to mess around.

Q: Along with your ~90 facet initiatives, 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 facet, relatively than with the tech. I’m certain some issues would actually pace up the conclusion of my designs although, so I ought to most likely no less than be taught some scripting and mess around with threading extra. Individuals have even been variety sufficient to produce some libraries and issues to assist on the market, however it’s simply tough to dam facet undertaking outing for tech studying when my facet undertaking time is for stress-free.

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

A: It’s most likely 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 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 strive Dwarf Fortress for your self, you possibly can download it from their website.

Tags: dwarf fortress, solo developer, video games

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