Hi, this is my first post on ROMhacking.net, as the title says, this post is about Mega Man 8 .PAC files and modding (for both PSX and Saturn), I don't plan on reconstructing disc image files — just for game structure reference and hopefully full-on modding efforts by others in the future —, so I won't be dealing with expanding disc image sizes and other similar things, I'll just be post my findings here.
Graphics aren't the things I'm most interested about, but they're the first thing I made a major discovery about: raw pixel data is stored at the end of a lot of .PAC files, found out by checking them in YY-CHR in the SNES 128x128 mode (this area is garbled in the Saturn files, I'll check this tool when I have access to my laptop later https://github.com/doyousketch2/SatRGB
In the same .PAC files, there's also some unknown data (and a decent amount of blank data), one of my wild assumptions of it is code, but there could be anything there, I'm pretty sure that — in the level/stage files —part of it is level data; I tried the Rockman 8 BMS script (and also an older version of BioFAT (BioHazard File Archive Tool)), but it only splits the files, sure it's good for separating blank, unknown and image data, but we still have the issue of reading the unknown data, the closest thing I could find that might be able to read this is an unreleased .PAC extraction tool that works for both PSX and Saturn .PAC files by MarkGrass mentioned in the reply in the link http://www.romhacking.net/forum/index.php?topic=17158.msg251100#msg251100
As for the other files, I don't know where the sound files are in the Saturn version from a glance of the filesystem (it's either somewhere in there, or the app I'm using forgot about the 2nd disc layer), along with the executable in the PSX version (might be SLUS_004.53); there are a couple of .BIN files in the Saturn version which go by the names LOGO.BIN and MAP.BIN, I don't have the means to check them now, but like I mentioned somewhere above, I'll see what I can find out about them when I have access to my laptop later; again in the Saturn version, there's a few WARNING*.BG files and a .TSK file (SDDRVS.TSK) that I didn't come across before.
We have the video files in their respective locations, sound files in the PSX version's SOUND folder, the Saturn-exclusive bonus files and RMs, 1STREAD.PRG and 2NDREAD.PRG are the Saturn executables, ASCII.DOT is probably the font, and a few text files in the Saturn version with Capcom copyright text for the title screen and ending.
I'm interested in finding out how the player works (i.e: movement, hitboxes, buster, etc.) along with finding out how the level data works, but that would probably require looking through the executables and debugging the game, maybe it'll be in the PLAYER.PAC file, who knows.
Anyway that's all for now, if I find out anything later, I'll post more in the replies - Arcade out.