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 initiatives 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 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 present engaged on a model with pixel graphics and a revamped UI that might 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 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 type of normal obeying manner, however form 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 Neighborhood. 

I take advantage of 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 do this myself in fact. 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 also be an actual ache, particularly now that I’m doing one thing past textual content graphics. I take advantage of FMOD for sound. 

All of this has been fixed over the course of the venture, 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 number of 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 lately I adopted SplitMix64, which was featured in a chat on the final Roguelike Celebration.

Q: What are the challenges in growing 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 take care of and alter?

A: It’s simple to neglect stuff! Trying to find ‘;’, which is a free methodology 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 identify my variables and objects persistently and memorably, and I go away sufficient comments round to remind myself of what’s occurring after I arrive at a spot of code. Generally it takes a number of searches to search 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 targeted solely on sure elements 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 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 sooner 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 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 knowledge constructions and so forth, although I’m undecided something is ever a refactor strictly right here since there’s at all times 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 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 in the end a mistake, however that was an enormous one. 

Q: Why was this was a mistake?

A: Whenever you declare a category that’s a type of merchandise, it locks you into that construction rather more tightly than when 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 “device” 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 underneath that umbrella. 

We do a number 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 tougher to do 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 totally different parts can simply be turned on and off, it’s simpler, and permits you to do extra. 

I feel some recreation builders check 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 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 typically that it turns into an optimization problem.

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

A: By no means! I’m struggling to think about a single problem. Luckily for us, we already had our byte sizes underneath management fairly nicely, 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 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 attributable to our different practices, fully accidentally. The primary problem was simply getting the time collectively to make the change, after which it didn’t find yourself taking almost so long as I assumed 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 just a part of it. We use A*, which is quick in fact, however it’s not adequate by itself. We will’t benefit from among the improvements on that (e.g. jump point) since our map modifications a lot. Usually, folks have used approaches that add varied bigger constructions 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 problem. So our method has been to only preserve observe of related parts 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 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 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 take care of, 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 present them some benefits although. However it’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. In fact, it is perhaps attainable with a extremely 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 undecided how unstable 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 pace hit, since we’d want to take care of two indices without delay, and one is unhealthy sufficient. Extra particular overlays can observe their pathing properties (and you then path by way of the overlays as a substitute of the tiles), however they’re exhausting and sluggish to take care of 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 features to be made there. We’re definitely on the fringe of what we will at present assist by way of brokers and map complexity, so one thing’ll have to present if we need to get extra out of it.

Q: On that observe, you’re simulating a number 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 number 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 initiatives/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 initiatives in it. A few of them lasted for days, some for a number of years. They’re largely different video games, virtually at all times in different genres, however there are additionally just a few 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 some other 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 certain some issues would actually pace up the belief of my designs although, so I ought to most likely not less than be taught some scripting and mess around with threading extra. Folks have even been sort sufficient to provide some libraries and issues to assist on the market, however it’s simply troublesome to dam facet venture day out for tech studying when my facet venture time is for stress-free.

Q: You will have essentially the most fascinating launch notes. What’s your favourite bug and what brought about 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 displaying up lifeless everywhere in 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 once 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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