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 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. 

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 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 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 under 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 sort of customary obeying means, 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 do 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 methods 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 undertaking, besides that SDL obtained launched a number of years in so we might do the ports. On the mechanical aspect of the sport, I don’t use lots 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 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 assume 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 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 occurring once I arrive at a spot of code. Typically 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 may be sort of an lively molten core that I’ve a significantly better working information of. There are a number 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 best way to go! Individuals clearly get good at doing it the opposite means, for instance over within the AAA video games context, and clearly a number of engineers are wanted over there to get issues achieved 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 via 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 simply needed to make?

A: There have been some refactors which have lasted for months, redoing sure knowledge buildings and so forth, although I’m unsure something is ever a refactor strictly right here since there’s at all times 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 probably the most mind-numbing factor I’ve in all probability ever achieved. Simply weeks and weeks and weeks of taking logic and performance calls that relied on X and Y and seeing how a Z suits 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 sort of merchandise, it locks you into that construction way more tightly than for those who simply have member parts. It’s good to have the ability to use digital capabilities and that sort 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 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 had been underneath that umbrella. 

We do lots 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 means tougher to do 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 completely different parts can simply be turned on and off, it’s simpler, and lets you do extra. 

I feel some recreation builders confer 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 a complete 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 typically that it turns into an optimization subject.

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

A: In no way! I’m struggling to consider a single subject. Thankfully 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 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 that 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, totally accidentally. The primary subject 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 much 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, nevertheless it’s not ok by itself. We are able to’t make the most of among the improvements on that (e.g. jump point) since our map adjustments a lot. Usually, folks have used approaches that add numerous bigger buildings on prime 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 strategy has been to simply preserve monitor of related parts reachable by strolling. These are fairly simple to replace even when the map adjustments shortly, 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 achieved, it’s good, typically. Then that permits 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 take care of, however the draw back is that the element indices are maintained for strolling solely. Which means flying creatures, as an example, don’t have international 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 present them some benefits although. Nevertheless it’s not supreme 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 outdoors makes an attempt. After all, it is likely to be doable with a extremely concerted effort, and I’ve seen different video games which have managed, as an example, some rectangular overlays and so forth that appear promising, however I’m unsure how risky or massive their maps had 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 monitor their pathing properties (and then you definitely path via the overlays as an alternative of the tiles), however they’re arduous and sluggish to take care of 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 actually on the fringe of what we are able to at the moment 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 lots 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 lots 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 tasks/applied sciences alongside DF?

A: Certain! The aspect 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, virtually at all times in different genres, however there are additionally a number 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 another 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 pace up the belief of my designs although, so I ought to in all probability a minimum of be taught some scripting and mess around with threading extra. Individuals have even been form sufficient to provide some libraries and issues to assist on the market, nevertheless it’s simply tough to dam aspect undertaking outing for tech studying when my aspect undertaking time is for enjoyable.

Q: You’ve gotten probably the most fascinating launch notes. What’s your favourite bug and what brought on 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 number of movies made about it by this level. That was the one the place the cats had been exhibiting up useless everywhere in the tavern ground, and it turned out they had been ingesting spilled alcohol once 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 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

More Posts