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[Anonymous], -Tom-
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rec98 th04 th05 pc98 position-independence uth05win meta

With no feedback to 📝 last week's blog post, I assume you all are fine with how things are going? Alright then, another one towards position independence, with the same approach as before…

Since -Tom- wanted to learn something about how the PC-98 EGC is used in TH04 and TH05, I took a look at master.lib's egc_shift_*() functions. These simply do a hardware-accelerated memmove() of any VRAM region, and are used for screen shaking effects. Hover over the image below for the raw effect:

Demonstration of an egc_shift_left() call

Then, I finally wanted to take a look at the bullet structures, but it required way too much reverse-engineering to even start within ¾ of a position independence push. Even with the help of uth05win – bullet handling was changed quite a bit from TH04 to TH05.

What I ultimately settled on was more raw, "boring" PI work based around an already known set of functions. For this one, I looked at vector construction… and this time, that actually made the games a little bit more position-independent, and wasn't just all about removing false positives from the calculation. This was one of the few sets of functions that would also apply to TH01, and it revealed just how chaotically that game was coded. This one commit shows three ways how ZUN stored regular 2D points in TH01:

… yeah. But in more productive news, this did actually lay the groundwork for TH04 and TH05 bullet structures. Which might even be coming up within the next big, 5-push order from Touhou Patch Center? These are the priorities I got from them, let's see how close I can get!