⮜ Blog

📝 Posted:
🚚 Summary of:
P0056
Commits:
b28cefc...c09446a
💰 Funded by:
rosenrose, [Anonymous]

No priorities, again…?! Please don't do this to me… 😕

Well, let's not continue with TH05 then 😛 And instead use the occasion to commit this interesting discovery, made by @m1yur1 last year. Yup, TH03's "ZUNSP" sprite driver is actually a "rebranded" version of Promisence Soft's SPRITE16.COM. Sure, you were allowed to use this driver in your own game, but replacing the copyright with your own isn't exactly the nicest thing to do… That now makes three library programmers that ZUN didn't credit. Makes me wonder what makes M. Kajihara so special. Probably the fact that Touhou has always been about the music for ZUN, first and foremost.

But what makes this more than a piece of trivia is the fact that Promiscence Soft's SPRITE16 sample game StormySpace was bundled with documentation on the driver. Shoutout to the Neo Kobe PC-98 collection for preserving he original release!

That means more documented third-party code that we don't necessarily have to reverse-engineer, just like master.lib or KAJA's PMD driver. However, the PC-98 EGC is rather complex and definitely not designed for alpha-tested 16-color sprite blitting. So it (once again) took quite a while to make sense of SPRITE16's code and the available documentation on the EGC, to come up with satisfying function names. As a result, I'm going to distribute the entire RE work related to TH03's SPRITE16 interface across a total of three pushes, this one being the first of them.

  • The second one will reverse-engineer the SPRITE16 code reachable from its interrupt handler, and also come with somewhat detailed English documentation on the PC-98 EGC raster ops in particular,
  • and the third one will cover TH03's sprite drawing functions, which look pretty undecompilable once again… (Update: 📝 Delivered and actually decompiled in P0060)

Next up, we do have more TH05 progress though, now for the first time specifically with position independence in mind. Pretty excited for this one!