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P0223, P0224, P0225
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rosenrose, Blue Bolt, Splashman, -Tom-, Yanga, Enderwolf, 32th System
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rec98 th02 th03 th04 th05 cutscene blitting micro-optimization glitch master.lib pc98 performance kaja unused meta midboss animation

More than three months without any reverse-engineering progress! It's been way too long. Coincidentally, we're at least back with a surprising 1.25% of overall RE, achieved within just 3 pushes. The ending script system is not only more or less the same in TH04 and TH05, but actually originated in TH03, where it's also used for the cutscenes before stages 8 and 9. This means that it was one of the final pieces of code shared between three of the four remaining games, which I got to decompile at roughly 3× the usual speed, or ⅓ of the price.
The only other bargains of this nature remain in OP.EXE. The Music Room is largely equivalent in all three remaining games as well, and the sound device selection, ZUN Soft logo screens, and main/option menus are the same in TH04 and TH05. A lot of that code is in the "technically RE'd but not yet decompiled" ASM form though, so it would shift Finalized% more significantly than RE%. Therefore, make sure to order the new Finalization option rather than Reverse-engineering if you want to make number go up.

So, cutscenes. On the surface, the .TXT files look simple enough: You directly write the text that should appear on the screen into the file without any special markup, and add commands to define visuals, music, and other effects at any place within the script. Let's start with the basics of how text is rendered, which are the same in all three games:

Superficially, the list of game-specific differences doesn't look too long, and can be summarized in a rather short table:

:th03: TH03 :th04: TH04 :th05: TH05
Script size limit 65536 bytes (heap-allocated) 8192 bytes (statically allocated)
Delay between every 2 bytes of text 1 frame by default, customizable via \v None
Text delay when holding ESC Varying speed-up factor None
Visibility of new text Immediately typed onto the screen Rendered onto invisible VRAM page, faded in on wait commands
Visibility of old text Unblitted when starting a new box Left on screen until crossfaded out with new text
Key binding for advancing the script Any key ⏎ Return, Shot, or ESC
Animation while waiting for an advance key None ⏎⃣, past right edge of current row
Inexplicable delays None 1 frame before changing pictures and after rendering new text boxes
Additional delay per interpreter loop 614.4 µs None 614.4 µs
The 614.4 µs correspond to the necessary delay for working around the repeated key up and key down events sent by PC-98 keyboards when holding down a key. While the absence of this delay significantly speeds up TH04's interpreter, it's also the reason why that game will stop recognizing a held ESC key after a few seconds, requiring you to press it again.

It's when you get into the implementation that the combined three systems reveal themselves as a giant mess, with more like 56 differences between the games. :zunpet: Every single new weird line of code opened up another can of worms, which ultimately made all of this end up with 24 pieces of bloat and 14 bugs. The worst of these should be quite interesting for the general PC-98 homebrew developers among my audience:

That brings us to the individual script commands… and yes, I'm going to document every single one of them. Some of their interactions and edge cases are not clear at all from just looking at the code.

Almost all commands are preceded by… well, a 0x5C lead byte. :thonk: Which raises the question of whether we should document it as an ASCII-encoded \ backslash, or a Shift-JIS-encoded ¥ yen sign. From a gaijin perspective, it seems obvious that it's a backslash, as it's consistently displayed as one in most of the editors you would actually use nowadays. But interestingly, iconv -f shift-jis -t utf-8 does convert any 0x5C lead bytes to actual ¥ U+00A5 YEN SIGN code points :tannedcirno:.
Ultimately, the distinction comes down to the font. There are fonts that still render 0x5C as ¥, but mainly do so out of an obvious concern about backward compatibility to JIS X 0201, where this mapping originated. Unsurprisingly, this group includes MS Gothic/Mincho, the old Japanese fonts from Windows 3.1, but even Meiryo and Yu Gothic/Mincho, Microsoft's modern Japanese fonts. Meanwhile, pretty much every other modern font, and freely licensed ones in particular, render this code point as \, even if you set your editor to Shift-JIS. And while ZUN most definitely saw it as a ¥, documenting this code point as \ is less ambiguous in the long run. It can only possibly correspond to one specific code point in either Shift-JIS or UTF-8, and will remain correct even if we later mod the cutscene system to support full-blown Unicode.

Now we've only got to clarify the parameter syntax, and then we can look at the big table of commands:

:th03: :th04: :th05: \@ Clears both VRAM pages by filling them with VRAM color 0.
🐞 In TH03 and TH04, this command does not update the internal text area background used for unblitting. This bug effectively restricts usage of this command to either the beginning of a script (before the first background image is shown) or its end (after no more new text boxes are started). See the image below for an example of using it anywhere else.
:th03: :th04: :th05: \b2 Sets the font weight to a value between 0 (raw font ROM glyphs) to 3 (very thicc). Specifying any other value has no effect.
:th04: :th05: 🐞 In TH04 and TH05, \b3 leads to glitched pixels when rendering half-width glyphs due to a bug in the newly micro-optimized ASM version of 📝 graph_putsa_fx(); see the image below for an example.
In these games, the parameter also directly corresponds to the graph_putsa_fx() effect function, removing the sanity check that was present in TH03. In exchange, you can also access the four dissolve masks for the bold font (\b2) by specifying a parameter between 4 (fewest pixels) to 7 (most pixels). Demo video below.
:th03: :th04: :th05: \c15 Changes the text color to VRAM color 15.
:th05: \c=,15 Adds a color map entry: If is the first code point inside the name area on a new line, the text color is automatically set to 15. Up to 8 such entries can be registered before overflowing the statically allocated buffer.
🐞 The comma is assumed to be present even if the color parameter is omitted.
:th03: :th04: :th05: \e0 Plays the sound effect with the given ID.
:th03: :th04: :th05: \f (no-op)
:th03: :th04: :th05: \fi1
Calls master.lib's palette_black_in() or palette_black_out() to play a hardware palette fade animation from or to black, spending roughly 1 frame on each of the 16 fade steps.
:th03: :th04: :th05: \fm1 Fades out BGM volume via PMD's AH=02h interrupt call, in a non-blocking way. The fade speed can range from 1 (slowest) to 127 (fastest).
Values from 128 to 255 technically correspond to AH=02h's fade-in feature, which can't be used from cutscene scripts because it requires BGM volume to first be lowered via AH=19h, and there is no command to do that.
:th03: :th04: :th05: \g8 Plays a blocking 8-frame screen shake animation.
:th03: :th04: \ga0 Shows the gaiji with the given ID from 0 to 255 at the current cursor position. Even in TH03, gaiji always ignore the text delay interval configured with \v.
:th05: @3 TH05's replacement for the \ga command from TH03 and TH04. The default ID of 3 corresponds to the ♫ gaiji. Not to be confused with \@, which starts with a backslash, unlike this command.
:th05: @h Shows the 🎔 gaiji.
:th05: @t Shows the 💦 gaiji.
:th05: @! Shows the ! gaiji.
:th05: @? Shows the ? gaiji.
:th05: @!! Shows the ‼ gaiji.
:th05: @!? Shows the ⁉ gaiji.
:th03: :th04: :th05: \k0 Waits 0 frames (0 = forever) for an advance key to be pressed before continuing script execution. Before waiting, TH05 crossfades in any new text that was previously rendered to the invisible VRAM page…
🐞 …but TH04 doesn't, leaving the text invisible during the wait time. As a workaround, \vp1 can be used before \k to immediately display that text without a fade-in animation.
:th03: :th04: :th05: \m$ Stops the currently playing BGM.
:th03: :th04: :th05: \m* Restarts playback of the currently loaded BGM from the beginning.
:th03: :th04: :th05: \m,filename Stops the currently playing BGM, loads a new one from the given file, and starts playback.
:th03: :th04: :th05: \n Starts a new line at the leftmost X coordinate of the box, i.e., the start of the name area. This is how scripts can "change" the name of the currently speaking character, or use the entire 480×64 pixels without being restricted to the non-name area.
Note that automatic line breaks already move the cursor into a new line. Using this command at the "end" of a line with the maximum number of 30 full-width glyphs would therefore start a second new line and leave the previously started line empty.
If this command moved the cursor into the 5th line of a box, \s is executed afterward, with any of \n's parameters passed to \s.
:th03: :th04: :th05: \p (no-op)
:th03: :th04: :th05: \p- Deallocates the loaded .PI image.
:th03: :th04: :th05: \p,filename Loads the .PI image with the given file into the single .PI slot available to cutscenes. TH04 and TH05 automatically deallocate any previous image, 🐞 TH03 would leak memory without a manual prior call to \p-.
:th03: :th04: :th05: \pp Sets the hardware palette to the one of the loaded .PI image.
:th03: :th04: :th05: \p@ Sets the loaded .PI image as the full-screen 640×400 background image and overwrites both VRAM pages with its pixels, retaining the current hardware palette.
:th03: :th04: :th05: \p= Runs \pp followed by \p@.
:th03: :th04: :th05: \s0
Ends a text box and starts a new one. Fades in any text rendered to the invisible VRAM page, then waits 0 frames (0 = forever) for an advance key to be pressed. Afterward, the new text box is started with the cursor moved to the top-left corner of the name area.
\s- skips the wait time and starts the new box immediately.
:th03: :th04: :th05: \t100 Sets palette brightness via master.lib's palette_settone() to any value from 0 (fully black) to 200 (fully white). 100 corresponds to the palette's original colors. Preceded by a 1-frame delay unless ESC is held.
:th03: \v1 Sets the number of frames to wait between every 2 bytes of rendered text.
:th04: Sets the number of frames to spend on each of the 4 fade steps when crossfading between old and new text. The game-specific default value is also used before the first use of this command.
:th05: \v2
:th03: :th04: :th05: \vp0 Shows VRAM page 0. Completely useless in TH03 (this game always synchronizes both VRAM pages at a command boundary), only of dubious use in TH04 (for working around a bug in \k), and the games always return to their intended shown page before every blitting operation anyway. A debloated mod of this game would just remove this command, as it exposes an implementation detail that script authors should not need to worry about. None of the original scripts use it anyway.
:th03: :th04: :th05: \w64
  • \w and \wk wait for the given number of frames
  • \wm and \wmk wait until PMD has played back the current BGM for the total number of measures, including loops, given in the first parameter, and fall back on calling \w and \wk with the second parameter as the frame number if BGM is disabled.
    🐞 Neither PMD nor MMD reset the internal measure when stopping playback. If no BGM is playing and the previous BGM hasn't been played back for at least the given number of measures, this command will deadlock.
Since both TH04 and TH05 fade in any new text from the invisible VRAM page, these commands can be used to simulate TH03's typing effect in those games. Demo video below.
Contrary to \k and \s, specifying 0 frames would simply remove any frame delay instead of waiting forever.
The TH03-exclusive k variants allow the delay to be interrupted if ⏎ Return or Shot are held down. TH04 and TH05 recognize the k as well, but removed its functionality.
All of these commands have no effect if ESC is held.
:th03: \wk64
:th03: :th04: :th05: \wi1
Calls master.lib's palette_white_in() or palette_white_out() to play a hardware palette fade animation from or to white, spending roughly 1 frame on each of the 16 fade steps.
:th03: :th04: :th05: \=4 Immediately displays the given quarter of the loaded .PI image in the picture area, with no fade effect. Any value ≥ 4 resets the picture area to black.
:th03: :th04: :th05: \==4,1 Crossfades the picture area between its current content and quarter #4 of the loaded .PI image, spending 1 frame on each of the 4 fade steps unless ESC is held. Any value ≥ 4 is replaced with quarter #0.
:th03: :th04: :th05: \$ Stops script execution. Must be called at the end of each file; otherwise, execution continues into whatever lies after the script buffer in memory.
TH05 automatically deallocates the loaded .PI image, TH03 and TH04 require a separate manual call to \p- to not leak its memory.
Bold values signify the default if the parameter is omitted; \c is therefore equivalent to \c15.
Using the \@ command in the middle of a TH03 or TH04 cutscene script
The \@ bug. Yes, the ¥ is fake. It was easier to GIMP it than to reword the sentences so that the backslashes landed on the second byte of a 2-byte half-width character pair. :onricdennat:
Cutscene font weights in TH03Cutscene font weights in TH05, demonstrating the <code>\b3</code> bug that also affects TH04Cutscene font weights in TH03, rendered at a hypothetical unaligned X positionCutscene font weights in TH05, rendered at a hypothetical unaligned X position
The font weights and effects available through \b, including the glitch with \b3 in TH04 and TH05.
Font weight 3 is technically not rendered correctly in TH03 either; if you compare 1️⃣ with 4️⃣, you notice a single missing column of pixels at the left side of each glyph, which would extend into the previous VRAM byte. Ironically, the TH04/TH05 version is more correct in this regard: For half-width glyphs, it preserves any further pixel columns generated by the weight functions in the high byte of the 16-dot glyph variable. Unlike TH03, which still cuts them off when rendering text to unaligned X positions (3️⃣), TH04 and TH05 do bit-rotate them towards their correct place (4️⃣). It's only at byte-aligned X positions (2️⃣) where they remain at their internally calculated place, and appear on screen as these glitched pixel columns, 15 pixels away from the glyph they belong to. It's easy to blame bugs like these on micro-optimized ASM code, but in this instance, you really can't argue against it if the original C++ version was equally incorrect.
Combining \b and s- into a partial dissolve animation. The speed can be controlled with \v.
Simulating TH03's typing effect in TH04 and TH05 via \w. Even prettier in TH05 where we also get an additional fade animation after the box ends.

So yeah, that's the cutscene system. I'm dreading the moment I will have to deal with the other command interpreter in these games, i.e., the stage enemy system. Luckily, that one is completely disconnected from any other system, so I won't have to deal with it until we're close to finishing MAIN.EXE… that is, unless someone requests it before. And it won't involve text encodings or unblitting…

The cutscene system got me thinking in greater detail about how I would implement translations, being one of the main dependencies behind them. This goal has been on the order form for a while and could soon be implemented for these cutscenes, with 100% PI being right around the corner for the TH03 and TH04 cutscene executables.
Once we're there, the "Virgin" old-school way of static translation patching for Latin-script languages could be implemented fairly quickly:

  1. Establish basic UTF-8 parsing for less painful manual editing of the source files
  2. Procedurally generate glyphs for the few required additional letters based on existing font ROM glyphs. For example, we'd generate ä by painting two short lines on top of the font ROM's a glyph, or generate ¿ by vertically flipping the question mark. This way, the text retains a consistent look regardless of whether the translated game is run with an NEC or EPSON font ROM, or the hideous abomination that Neko Project II auto-generates if you don't provide either.
  3. (Optional) Change automatic line breaks to work on a per-word basis, rather than per-glyph

That's it – script editing and distribution would be handled by your local translation group. It might seem as if this would also work for Greek and Cyrillic scripts due to their presence in the PC-98 font ROM, but I'm not sure if I want to attempt procedurally shrinking these glyphs from 16×16 to 8×16… For any more thorough solution, we'd need to go for a more "Chad" kind of full-blown translation support:

  1. Implement text subdivisions at a sensible granularity while retaining automatic line and box breaks
  2. Compile translatable text into a Japanese→target language dictionary (I'm too old to develop any further translation systems that would overwrite modded source text with translations of the original text)
  3. Implement a custom Unicode font system (glyphs would be taken from GNU Unifont unless translators provide a different 8×16 font for their language)
  4. Combine the text compiler with the font compiler to only store needed glyphs as part of the translation's font file (dealing with a multi-MB font file would be rather ugly in a Real Mode game)
  5. Write a simple install/update/patch stacking tool that supports both .HDI and raw-file DOSBox-X scenarios (it's different enough from thcrap to warrant a separate tool – each patch stack would be statically compiled into a single package file in the game's directory)
  6. Add a nice language selection option to the main menu
  7. (Optional) Support proportional fonts

Which sounds more like a separate project to be commissioned from Touhou Patch Center's Open Collective funds, separate from the ReC98 cap. This way, we can make sure that the feature is completely implemented, and I can talk with every interested translator to make sure that their language works.
It's still cheaper overall to do this on PC-98 than to first port the games to a modern system and then translate them. On the other hand, most of the tasks in the Chad variant (3, 4, 5, and half of 2) purely deal with the difficulty of getting arbitrary Unicode characters to work natively in a PC-98 DOS game at all, and would be either unnecessary or trivial if we had already ported the game. Depending on where the patrons' interests lie, it may not be worth it. So let's see what all of you think about which way we should go, or whether it's worth doing at all. (Edit (2022-12-01): With Splashman's order towards the stage dialogue system, we've pretty much confirmed that it is.) Maybe we want to meet in the middle – using e.g. procedural glyph generation for dynamic translations to keep text rendering consistent with the rest of the PC-98 system, and just not support non-Latin-script languages in the beginning? In any case, I've added both options to the order form.

Surprisingly, there was still a bit of RE work left in the third push after all of this, which I filled with some small rendering boilerplate. Since I also wanted to include TH02's playfield overlay functions, 1/15 of that last push went towards getting a TH02-exclusive function out of the way, which also ended up including that game in this delivery. :tannedcirno:
The other small function pointed out how TH05's Stage 5 midboss pops into the playfield quite suddenly, since its clipping test thinks it's only 32 pixels tall rather than 64:

Good chance that the pop-in might have been intended. There's even another quirk here: The white flash during its first frame is actually carried over from the previous midboss, which the game still considers as actively getting hit by the player shot that defeated it. It's the regular boilerplate code for rendering a midboss that resets the responsible damage variable, and that code doesn't run during the defeat explosion animation.

Next up: Staying with TH05 and looking at more of the pattern code of its boss fights. Given the remaining TH05 budget, it makes the most sense to continue in in-game order, with Sara and the Stage 2 midboss. If more money comes in towards this goal, I could alternatively go for the Mai & Yuki fight and immediately develop a pretty fix for the cheeto storage glitch. Also, there's a rather intricate pull request for direct ZMBV decoding on the website that I've still got to review…