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 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 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 entire 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 mission, 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 will probably be accessible 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 employ? 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 form of customary obeying approach, 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 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 try this myself after all. I’m unsure if I’d use one thing like Unity or Unreal now if I had the selection since I don’t know how you can 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 mission, besides that SDL received launched a number of years in so we may do the ports. On the mechanical facet of the sport, I don’t use lots 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 just lately I adopted SplitMix64, which was featured in a chat on the final Roguelike Celebration.

Q: What are the challenges in growing a single mission 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 keep up and alter?

A: It’s simple to overlook stuff! Looking for ‘;’, which is a unfastened methodology however shut sufficient, we’re as much as 711,000 strains, so it’s simply not potential to maintain all of it in my head now. I attempt to title my variables and objects persistently and memorably, and I go away 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 search 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 targeted solely on sure elements of the sport, so there may be form of an lively molten core that I’ve a a lot 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, definitely for me, who has no expertise engaged on a big multi-person mission, that is the way in which to go! Individuals 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 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, nevertheless it’s true that I don’t have any team-oriented or bureaucratic hurdles to leap by once I need to make an alteration. I can simply go do it. However I additionally must do it alone.

Q: What’s the most important 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 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 a giant one. 

Q: Why was this was a mistake?

A: Once you declare a category that’s a form of merchandise, it locks you into that construction far 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 “instrument” 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 recreation had been below that umbrella. 

We do lots of procedural era, and if we needed to, say, generate an merchandise that acts partially like one factor and partially like one other, it’s simply approach more durable to try this if 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 lets you do extra. 

I feel some recreation builders seek advice from 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 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 instrument merchandise aren’t used so usually that it turns into an optimization subject.

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

A: Under no circumstances! I’m struggling to think about a single subject. Thankfully for us, we already had our byte sizes below 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 that may have gotten us in hassle. It simply ended up being actually good code for 64 bit conversion on account of our different practices, completely by chance. The primary subject was simply getting the time collectively to make the change, after which it didn’t find yourself taking almost so long as I believed it could.

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 simply 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 number of 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 keep up, or are in any other case a trouble. So our strategy has been to simply maintain monitor of linked parts 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 completed, 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 keep up, 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 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. But it surely’s not excellent 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. After all, it may be potential 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 unstable or giant 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 keep up two indices directly, and one is unhealthy sufficient. Extra particular overlays can monitor their pathing properties (and then you definately path by the overlays as a substitute of the tiles), however they’re arduous and gradual 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 features to be made there. We’re definitely on the fringe of what we will at present help when it comes to brokers and map complexity, so one thing’ll have to offer if we need to get extra out of it.

Q: On that notice, you’re simulating lots of issues all of sudden—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 initiatives/applied sciences alongside DF?

A: Certain! The facet mission 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 at all times in different genres, however there are additionally a number of DF helper initiatives, like the parable generator prototype. Nothing near seeing the sunshine of day, nevertheless it’s enjoyable to mess around.

Q: Together with your ~90 facet initiatives, have you ever explored some 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, reasonably than with the tech. I’m certain some issues would actually pace up the conclusion 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 facet mission trip for tech studying when my facet mission time is for enjoyable.

Q: You’ve got probably the most attention-grabbing launch notes. What’s your favourite bug and what precipitated 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 flooring, 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 by 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 possibly can download it from their website.

Tags: dwarf fortress, solo developer, video games

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