State of the project?

[rockmanomega]

Hello!

I am writing here since it seems like the decompilation seems to be...mostly complete from what I am gathering? There's even an active portable branch. However, I don't see a lot of documentation on either how the decompilation is doing in terms of either a video showcase, or similar. Nor much about how the portable or remastered branches are working, which I assume are different projects altogether within.

Is it fair to say that EoSD has been mostly decompiled for starters? Is the reason why is not hitting 100% similar to the case of Lego Island where the accuracy of the binary comes down to a specific set of conditions that were produced by ZUN's compiler back in the day? Just curious.

Cheers!
RockmanOmega.

[roblabla]

Heyo,

As far as behavior goes, the decompilation is mostly complete - we're supposed to be bug-for-bug accurate. Most of the functions compile down to the same assembly, and those that don't have trivial differences that shouldn't affect the behavior of the function.

The remaining work on the decomp side is:

1. Fixing those small differences
2. Reordering the functions so they appear in the same order in the binary as the official game. This ordering is proving to be problematic because of some as-of-yet unexplained behavior WRT inlined functions defined in header files.
3. Checking that the data/rodata section is correct (reordering as necessary too). We've found some small bugs in our decomp caused by some small mistakes in the data section.

---

As far as progress documentation goes, yeah that's my bad, I've never been very good at playing the social media game. Essentially the game is in a 100% playable state, and can be used as a drop-in replacement for the original game.

As far as portable/remastered branches, those are separate branches to fix bugs and make it work on other platforms like linux or more modern windows without hacks. I'm not involved in them (mostly due to lack of time), the main drivers behind them are wearrrrr, toadster172 and KSSBrawl.

Thanks for the interest!
roblabla

[rockmanomega]

Hello, yes thank you for answering!

Awesome! I am glad that a decompilation of a Windows Touhou game has been achieved! I'd like to offer a few more questions since I am curious on this:

A) I've noticed that there's a separate repo for IN, I assume this is because the objective is to also decompile that game to my knowledge? If that's the case. Does that means the objective is to have a working decompilation of more Windows Touhou games in general? Games like PCB, MoF or similar?

B) Assuming the above is correct, would the result of the decompiled EoSD game help for the other games? My understanding of the subject is that ZUN used a custom scripting language to hardcode the enemy behavior and patterns of his games, so I am wondering if this is similar to something like 'decompile the bits that makes the game run and get ECL as is' for faster decomps? Just wondering.

Cheers!
RockmanOmega.

[roblabla]

I've noticed that there's a separate repo for IN, I assume this is because the objective is to also decompile that game to my knowledge? If that's the case. Does that means the objective is to have a working decompilation of more Windows Touhou games in general? Games like PCB, MoF or similar?

Some members of the community are working on reverse engineering and decompiling the other games based on the "1st generation windows" engine, so PCB and IN. MoF has a completely new engine, and I don't think anyone's working on it right now.

Assuming the above is correct, would the result of the decompiled EoSD game help for the other games? My understanding of the subject is that ZUN used a custom scripting language to hardcode the enemy behavior and patterns of his games, so I am wondering if this is similar to something like 'decompile the bits that makes the game run and get ECL as is' for faster decomps? Just wondering.

Absolutely, the EosD decomp helps a ton for the other games of the same engine. For starters, the general structure of the engine has not changed much across the games, so a good chunk of how the game is organized, the different classes and whatnot, are essentially the same across the three 1st gen engine games, which gives us a pretty big headstart.

Generally speaking, the game executable itself is really just a generic engine with very little game behavior hardcoded in it. Most of the thing that drive the main "game" is, as you say, encoded in separate "scripting" files. Those scripting files are found in the various DAT files next to the main game executable. Within it, you've got:

• ECL for the level logic, ergo what enemies to spawn where and when, how the enemy moves and the bullet patterns it shoots, with which dialogue to play when
• ANM for animation logic + all the textures in the game.
• MSG for the actual dialogue scripts.

To be sure, the game engine still has a bit of game-specific logic in it (player movement, player bullet/bomb patterns, the number of levels available, some "non-game" aspects like the menus and whatnot), but a good deal of the game engine's code is dealing with those files.

Now, to be clear, we didn't reverse engineer the contents of those files. This was already done by other people, and we have a great tool, truth, which is able to turn ECL/ANM/MSG files to something similar to "source code", and back to ECL files.

What we did do, however, is reverse engineer the way the game engine parses and executes those files. And this is usable as a base for a decompilation effort for the other games using the same engine, as the structure of those scripting engines are relatively untouched, with only some (a lot of) added instructions and a few reworks here and there.

FWIW, for some pointers on the various pieces of code:

• The "ECL Timeline" (the thing that controls what enemies to spawn or dialogue to play at a given time during a level) is found here
• The "ECL Enemy Behavior" (how enemies move and bullet patterns they spawn) is found here
• The "ANM VM" (how animations play) is found here
• The "MSG VM" (dialogue stuff) is here

[rockmanomega]

Awesome! And nice to know that we have several tools that can tackle this many moving parts!

I am particularly hoping for both PCB and IN since I got quite a few memories with those games, specially PCB. I would like to ask something about the newer engines though, I have heard that MoF's new engine is something completely new and rewritten by ZUN. But I've also heard that, starting from MoF, the engine has remained relatively the same since? So any efforts on that game would get us closer to achieving the functionality for the rest of the games, just like EoSD is the base for 1st gen like you mentioned with PCB and IN. Just wondering though.