folkulore – 46 OkuMen

Modifying text display ASM in Rusty (FolkuLore, part 4)

March 5, 2019 hollowaytape FolkuLore

When a game’s developer writes code, they usually* do it in a reasonably high-level language like C++. They have access to all sorts of nice things like variable names, function labels, comments, and so forth. When it comes time to run the code, it is compiled through something like Borland Turbo C++, and it is translated into assembly language (ASM) for the target platform, in this case the PC-98’s x86 processor. The compilation process strips away all of the useful names of things, determines exactly how all of the data needs to move between registers and memory, and does what it can to optimize the program. This much more difficult-to-understand code is what remains in the final .EXE that ships on the game disk. Since we don’t have the source code, we need to look to the ASM in order to understand and modify the game.

I had a lot of unsuccessful interactions with assembly language, across several projects, before I was finally able to successfully modify it, which I needed to for Rusty.

Compression in Rusty (FolkuLore, part 3)

November 20, 2018 hollowaytape FolkuLore

While we were finishing up the E.V.O. translation, we weren’t sure whether we wanted to work on more translations together. Our group didn’t even have a name yet. But we were starting to test the waters a little bit. Kuoushi was looking at Libros de Chilam Balam, and I was hearing about some other games in the PC-98 Discord server. I came across a tweet from another PC-98 romhacker, Nana, who had this to say about Rusty:

Rusty is the primary reason this little collage got out two days later than I had intended, haha. Game's code is a nightmare.

— Nana (@Nana_VS_Nana) September 1, 2016

I had at least heard of the game before from its HG101 article, and for some reason I wanted a challenge.

Rusty was kind of a weird project in retrospect – it’s in a genre we usually ignore (hard action platformer), it looks an awful lot like it’d be a hentai game (which we just claimed we wouldn’t work on), and it doesn’t even have that much text. But it was where I started to develop some proper romhacking skills, like assembly modification and handling data compression

.GDT images in E.V.O. (FolkuLore, part 2)

October 2, 2018 hollowaytape FolkuLore

Last time, we looked at a problem that turned out to be far easier for hacking a PC game than a console one. Today, we’re looking at a problem that is really only an issue for PC games.

These older game consoles tend to have specialized graphical hardware that works in terms of sprites and tiles, so their graphics are stored in a similar way from game to game. The PC-98 is a business computer that’s really good at displaying high-resolution text, but graphics-wise, programmers had to roll their own solutions for everything. As a result, pretty much every developer created and used their own proprietary format for storing graphics. E.V.O.’s developer, Almanic, used a format called .GDT.

Text encoding in E.V.O. (FolkuLore, part 1)

September 25, 2018 hollowaytape FolkuLore

Hi! This is hollowaytape, the hacker/developer for 46 OkuMen. Today marks three years since we formed this group. We’re hard at work on some non-technical parts of our current and future projects, so I thought I would take this chance to write a little series about my prouder moments from our first handful of translation hacks.

First, I will describe the process of random flailing, blind luck, and help from others that led to the key breakthroughs of our first few projects. Then, I’ll step through a few of the more impressive technical things I could accomplish once I had a firmer grounding in x86 assembly. Finally, I’ll talk about some of the absurd technical hurdles I’ve found in games we haven’t picked up as projects, which I haven’t been able to solve.

They aren’t tutorials or rigorous technical documents. Instead, I’m hoping just to give you a taste of what PC-98 romhacking is like, give some advice if you’re tackling a similar problem, and share some amusing and dumb things I thought along the way.