The pascal calling convention for TH03's input mode functions actually
sort of matters, since we have this nice function pointer type that
expects pascal.
Yeah… such fun pretending that the original code wasn't copy-pasted.
And yes, Reimu will have to wait until the next one.
Completes P0037, funded by zorg.
And if I don't manage to cover Reimu in this push, it's because ZUN
switched around the cases in half of the functions here… 😵 Here's
some macros instead, to make the code at least *look* as table-driven
and readable as it should have been in the first place.
Part of P0037, funded by zorg.
Ooh, shot position being determined by RNG at lower shot levels? That's
some RNG manipulation TAS potential right there! Maybe.
Part of P0037, funded by zorg.
That should make this convoluted copypasta a bit easier to read. And
sure, I could have done something about the loop as well, but
SHOT_FUNC_INIT already hides enough control flow behind a macro…
Part of P0037, funded by zorg.
A TH05 innovation that actually makes the game code easier to read?!
Although it was quite hard to actually reverse-engineer it, with the
confusing flag ordering pointing to some deeper meaning behind the
flags, which really doesn't exist.
Completes P0036, funded by zorg.
It seems that the main th0?/ directories should only contain actual
translation units (of which there are more than previously assumed)
as well as other not really further classifiable slices?
Part of P0036, funded by zorg.
And once again, the TH05 version is un-decompilable. :/ It was pretty
close this time, though, as the entire block between PUSH DI and POP DI
kind of resembles a separate inlined function, in accordance with Turbo
C++'s automatic backup of the DI register, as researched in 7f971a0.
Except that it contains a loop, and Turbo C++ refuses to inline any
function with `do`, `while`, `for`, or `goto`. If it didn't, it would
have totally worked.
Also, yes, C++ class methods are treated identically in this regard.
Oh well. Shot type control functions next, finally!
Completes P0035, funded by zorg.
Yes, if you collect more than 255 point items in one TH04 stage, the
counter will overflow to 0.
It's a 16-bit word in both TH02 and TH05.
Part of P0034, funded by zorg.
So it's *_put(), inherited from master.lib, for everything just writing
to text RAM, and *_render() for everything more involved? But what
about master.lib's own graphics RAM functions like super_put()? Need to
fix that inconsistency some day.
Once again no decompilation, because…
Part of P0033, funded by zorg.
The TH02 version is a piece of cake…
… but TH04 starts turning it into this un-decompilable piece of
unnecessarily micro-optimized ZUN code. Couldn't have chosen anything
better for the first separate ASM translation unit.
Aside from now having to convert names of exported *variables* to
uppercase for visibility in ASM translation units, the most notable
lesson in this was the one about avoiding fixup overflows. From the
Borland C++ Version 4.0 User's Guide:
"In an assembly language program, a fixup overflow frequently
occurs if you have declared an external variable within a
segment definition, but this variable actually exists in a
different segment."
Can't be restated often enough.
Completes P0032, funded by zorg.
Rule of thumb going forward: Everything that emits data is .asm,
everything that doesn't is .inc.
(Let's hope that th01_reiiden_2.inc won't exist for that much longer!)
Part of P0032, funded by zorg.
"Yeah, let's do this real quick, how can this possibly be hard, it's
just MOVs and a few function calls"…
…except that these MOVs access quite a lot of data, which we now all
have to declare in the C world, hooray.
Once it came to midbosses and bosses, I just turned them into C structs
after all. Despite what I said in 260edd8… after all, the ASM world
doesn't care about the representation in the C world, so they don't
necessarily have to be the same.
Since these structs can't contain everything related to midbosses and
bosses (really, why did all those variables have to be spread out like
this, ZUN?), it also made for a nice occasion to continue the "stuff"
naming scheme, describing "an obviously incomplete collection of
variables related to a thing", first seen in 160d4eb.
Also, PROCDESC apparently is the only syntactically correct option to
declare an extern near proc?
Also, that `boss_phase_timed_out` variable only needs to be here
already because TCC enforces word alignment for the .data segment…
yeah, it's technically not related to this commit, but why waste time
working around it if we can just include that one variable.
Completes P0030, funded by zorg.
I've had the idea to hide this implementation detail and improve code
readability for some time now, but it obviously must still all inline,
to be indistinguishable from a direct assignment of the correct value…
… which, amazingly, it does! Even the static_cast from float to int.
The latter allows us to exclusively implement this for float, since we
do have to express the occasional value smaller than 16.
Who needs macros anyway. Yay, C++ in TH04 and TH05 after all!
Part of P0030, funded by zorg.
… yeah, I don't really like these ambiguous "mode" and "mode change"
variable names either, but what's the alternative? Something something
"sub-phase", to distinguish them from regular phases? Feels way too
early to decide on something more specific. And pretty much nothing I
could come up with right now would have made their inconsistent use any
clearer.
But I need to decide on *something* before moving on, so… eh, let's
just go with what uth05win chose.
Also, yeah, dealing with those 0xFE and 0xFD boss_phase constants some
other time 😛
Also, today in "Weird TASM crashes": Trailing commas at the end of
`public` lines…
Completes P0028, funded by zorg.
Many thanks to http://bytepointer.com/tasm/index.htm for providing a
better searchable resource for TASM's default `LEA imm16` → `MOV imm16`
optimization, which we initially had to hack around here.
Funded by -Tom-.
So apparently, this way of distorting a circle into an ellipse (?) by
adding a value to the angle for one of the two coordinates isn't
actually widely known in math and doesn't have a name. Fair enough.
Funded by -Tom-.
Sure, I like me some global variables too. If you have to temporarily
replace them for a single function call though, it's pretty much the
textbook example of where *not* to use them.
Funded by -Tom-.
Yup, nothing interesting in here.
Except for maybe the confirmation that LS00.BB is used for the curved
bullets used by Shinki and EX-Alice?
Funded by -Tom-.
… because TH04's version of this takes the ASCII stage ID directly from
the resident structure.
So boss battles are simply triggered by setting the background tile
scroll speed to 0? That means…
Funded by zorg.
Again, one of these functions that ZUN *probably* wrote in ASM for shits
and giggles, which you *again could* "decompile" using in-line assembly,
but that kind of defeats the point.
Oh well, at least the fact that the parameter is passed in AL means that
the calling convention must have been __fastcall, and *that* part *does*
cleanly map to C. Unlike some of the functions in d08a7f4.
Funded by zorg.
Struct strLASER in uth05win… except that the member names in that one
were not only a bit too unclear, but `ageThres` and `shootAgeThres`
should have also been the other way round.
Also, yes, TH04's laser structure seems completely different.
Funded by -Tom-.
With TH05 definitely being the Galaxy Brain version of this function.
You'll see once I get to push the C decompilation for that one…
Anyway, that covers all shared input functions of TH02-TH05!
Funded by zorg.
Seemingly included in every other larger structure describing anything
remotely sprite-like. Couldn't find this in the earlier games,
unfortunately…
Funded by zorg.
TH02 just seems to use a sequence of branches in sub_D6CA.
I thought about keeping variable and function names consistent with
uth05win (on which most upcoming reverse-engineering commits will be
based). But as it will turn out, it ignored a certain very important
substructure, so I don't think it's worth introducing this naming style
clash.
Funded by zorg.
Yes, you're reading that correctly. If the cursor is at 255, reading a
16-bit value will fill the upper 8 bits with the neighboring cursor
value, which always is 0xFF.
Funded by -Tom-.
Oh, right, these functions can have parameters. So, let's turn snd_kaja_func()
into a macro that combines the function number and the parameter into the AX
value for the driver.
And renaming them all to the short filenames they will be decompiled to for
consistency. These functions aren't really immediately hardware-related, as
we've established earlier in the decompilation.
Yes, all of it. Including the bouncing polygons, of course. And since it's
placed at the end of ZUN's code inside the executable, the code's already
position-independent and fully hackable.
Also covering the two variations for blitting only every second row or
blitting only a 320x200 quarter, as seen in the endings.
So yeah, there's indeed nothing wrong with piread.cpp. TH03 just uses that
separate function that only blits every second row of an image, and indeed
always loads the entire image as it would appear in a PNG conversion. Here's
what happens if you display these images using the non-interlacing function:
https://www.dropbox.com/s/885krj09d9l0890/th03%20PI%20no%20interlace.png
With TH03 changing the calling convention for most of the code from __cdecl to
__pascal, I've been getting more and more confused about this myself. So,
let's settle on the following consistent syntax for function calls:
* C where the calling convention is actually __cdecl and where TASM's emitted
__cdecl code matches the original binary
* PASCAL where the calling convention is actually __pascal
* STDCALL where the calling convention is actually __cdecl, but where
the caller either defers stack cleanup (summing up the stack size of
multiple functions, then cleaning it all in a single "add sp" instruction)
or where the stack is cleared in a different way (e.g. "pop cx").
Unfortunately though, when using the ARG directive to automatically generate
an appropriate RET instruction for the given calling convention, TASM always
emits ENTER and LEAVE instructions even when no local variables are declared,
which greatly limits the number of functions where we can use that syntax. -.-
Well, the naming.
Even though only TH02 actually uses MIDI (and thus, the MMD driver), every
game since then contains interrupt instructions for both functions. We could
just name it "pmd", since it seems like that's what came first - the AH
numbers of the 6 functions that make up MMD's interrupt API are identical to
those of the equivalent functions in PMD, even including gaps in the numbering
for PMD functions that don't have an equivalent in MIDI. However, except for
the FM sound effect handling and the key display in TH05's Music Room, these 6
functions are all the games actually use. Also, we already distinguish between
PMD and MMD in the driver check functions, and it might be confusing to only
imply PMD from now on?
So, "kaja" it is, collectively referring to the shared aspects of both
drivers.
Yup, packfiles finally proved that we really have a different set of changes
to master.lib in every game. Also, there are bound to be more of these game-
specific small changes to otherwise identical code in ZUN's own code.
And hey, no need to define that value in the build scripts anymore.
(I've also considered just copying modified versions into the individual game
subdirectories, but it's not too nice to expect people to diff them in order
to actually understand why these copies exist and where the changes actually
are.)
32th System
