Yes, decompilation, of something that was so obviously originally
written in ASM. We're still left with two un-decompilable instructions
here, but I'm amazed at how nicely I was able to abstract away all of
the gory register details, leading to pretty clear, readable, and dare
I say *portable* code?! Turbo C++ was once again pretty helpful here:
• `static_cast<char>(_BX) = _AL` actually compiles into `MOV BL, AL`,
as you would have intended,
• and no-op assignments like _DI = _DI are optimized away, allowing
us to leave them in for clarity, so that we can have all parameter
assignments for the SPRITE16 display call in a single place.
I love this compiler.
Part of P0060, funded by Touhou Patch Center.
Yup, function parameters that can clearly be identified as coordinates
are by far the fastest way to raise the calculated position
independence percentage. Kinda makes it sound like useless work, which
I'm only doing because it's dictated by some counting algorithm on a
website, but decompilation will want to un-hex all of these values
anyway. We're merely doing that right now, across all games.
Part of P0058, funded by -Tom-.
Aha! TH03's in-game graphics run in line-doubled 640×200 simply because
that's what this SPRITE16.COM version was written for, making use of
the PC-98 EGC for optimized blitting.
Doesn't seem all *too* optimized though, given that it chooses to
effectively draw every sprite twice, just in case it might overlap with
something that's already in VRAM. It first clears the previous VRAM
content at the drawing position according to the sprite's alpha mask,
then ORs in the actual sprite data. The EGC can do monochrome alpha-
tested blitting just as well as the GRCG, but once the sprite data
covers all bitplanes, ORing is apparently the best it can do by itself?
More technical details on the raster operations in the next push!
Completes P0056, funded by rosenrose and [Anonymous].
Which was actually found out by @m1yur1 last year, who thankfully
tweeted this in reference to ReC98:
https://twitter.com/m1yur1/status/1018855232371998720
Thanks a lot! But what makes this more than a piece of trivia is the
fact that the StormySpace release actually *was* bundled with
documentation. Shoutout to the Neo Kobe PC-98 collection for preserving
the original release! This should now greatly simplify any RE efforts
related to TH03's INT 42h calls. (Not *trivialize*, because there's
still all this EGC hardware to be understood…)
And 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.
Part of P0056, funded by rosenrose and [Anonymous].
nmlgc