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Posted by patrickhulin 2 days ago

Reverse Engineering SimTower(phulin.me)
This is the story of building https://towers.world, a ~perfect, tick-for-tick reproduction of 1993 game SimTower.

I spent weeks reverse-engineering the original EXE and writing up a detailed spec of how the simulation actually works under the hood — population flow, elevator AI, the whole star-rating system. The specs are all on GitHub if you want to read them: https://github.com/phulin/tower-together/tree/main/specs

It's also collaborative. Multiple players can connect to the same tower, the simulation keeps running as long as anyone's connected, and build actions sync across clients in real time.

Because I rebuilt the UI, I could add features like shift-click to build grids of rooms - instead of painstakingly clicking to build rows of offices and hotels, shift-click allows a 10-floor grid to be built all at once.

The game runs on Cloudflare Durable Objects, one of my favorite web primitives.

Everything is open source: https://github.com/phulin/tower-together

165 points | 29 comments
ok_dad 47 seconds ago|
I love you this was the best sim game when I was a kid Abe now I’ll spend my weekend on your site!
johnfn 4 hours ago||
First of all, super cool. I have a soft spot for SimTower as well. :)

> I didn’t want to do a function-by-function port. First, APIs may be copyrightable - and copying a binary that closely might implicate copyright more than an approach closer to clean-room design. But it was clear that I needed some level of feedback from the ground-truth binary in order to provide a hill for the LLM to climb on the reimplementation.

Interesting, but isn't this what, say, the Ocarina of Time reverse engineer port does[1]? I imagine the fact that this hasn't been served a takedown notice from Nintendo is a proof that it's defensible? Or at least that there's precedent, ha.

Anyway, this is really cool. I genuinely think the only thing that's missing for me to waste an afternoon here is the sound effects!

[1]: https://github.com/zeldaret/oot

jlev1 7 hours ago||
Wow!

There was a little-known sequel to SimTower called Yoot Tower (named after Yoot Saito). It was a commercial flop, but I played it in the 2000s and again in the 2010s and very much enjoyed it! It had a lot of added customizability (more choices of restaurants and shops, for one thing). I would love to see that game recreated.

zamadatix 5 hours ago||
Project Highrise is also worth checking out. It's a 2016 re-imagination of the same type of game. I'm not sure I enjoyed it as much as I did Yoot Tower... but I'm also not sure if that's just because Yoot Tower was a few decades younger back when I played :).
pixelcort 7 hours ago|||
One of the maps in Yoot Tower is Kegon Falls. When I moved to Japan I found out it was a real place. Just took another day trip up there last month. Of course IRL it’s just an elevator but the view each season is amazing.
thispbowden 7 hours ago||
Love Yoot Tower! Can we clone it next?
patrickhulin 7 hours ago||
yes! I've been thinking about how to do it, but it will take some work!
LostMyLogin 1 hour ago||
> First, the AI makes premature conclusions about subsystems, records them, and then struggles to figure out when to abandon its earlier guesses.

This perfectly describes what feels off to me about Opus 4.7 (unsure if that’s what you are using). It seems to go down an incorrect path, I correct it, but it still references things from it. Trying to direct it back becomes a mess.

Has anyone experience this as well or am I going crazy? Doesn’t happen with 4.6 for me.

appplication 41 minutes ago|
I’ve had not great experiences with Opus 4.7. It seems the model is overall less effective at reliably delivering via my standard way of interacting, and it also forgets things it was asked several times, even just minutes after being reminded again (e.g. “don’t in-line imports”).

I’m probably holding it wrong, but I think a given a sufficiently advanced AI it would essentially be impossible to use it incorrectly. Feels like a step backwards in this regard.

ChickeNES 42 minutes ago||
Heh, I have four different games I am currently experimenting with, luckily I skipped this one as I am still expecting the original/Yoot source will be published (hopefully DonHopkins sees this and it nudges him to get it uploaded!).
swyx 1 hour ago||
> This project used an absolutely ridiculous number of tokens. I had to upgrade to the Claude Code $200/month plan and carefully avoid usage in the 8 AM-2 PM 2x peak window.

that doesnt sound too terrible to be honest. TIL that 8am-2pm is 2x usage.

MrPowerGamerBR 4 hours ago||
Just a fyi for anyone that doesn't know: A few years back Don Hopkins got the permission from Yoot Saito to open source Yoot Tower, SimTower's sequel: https://github.com/YootTowerManagement/YootTower

...however I don't think that the source was ever published anywhere, considering that the repository still doesn't have the source code yet. ("Please check out the YootTower repo, where I'll publish the source code once it's cleaned up, reviewed and approved by Yoot, and relicensed with the MIT licensed.")

grogenaut 2 hours ago||
I played when I was a kid. I figured out you could just build condos like crazy and make money pause build more, and repeat, get tons of money, build all the way up. But I couldn't figure out how to get people to the top level for that achievement.

I'm gonna Google that and see what I got wrong

manwe150 39 minutes ago|
I see to recall it being an express elevator to floor 90 (multiple of 15), then a short regular elevator for the rest of the way to the cathedral. I beat the game several times, usually with the 100% lowest-cost office build.
qingcharles 2 hours ago|
Can you talk about how you actually disassembled the EXE and reverse-engineered it?
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