📝 Posted:

2023-05-01 23:56 UTC

🚚 Summary of:

P0238, P0239

⌨ Commits:

(Website) 4698397...edf2926, c5e51e6...P0239

💰 Funded by:

Ember2528

🏷 Tags:

website+ th01- meta+ anniversary-edition+ debloating+ master.lib+ cutscene+ animation+ debug-

Stripe is now properly integrated into this website as an alternative to PayPal! Now, you can also financially support the project if PayPal doesn't work for you, or if you prefer using a provider out of Stripe's greater variety. It's unfortunate that I had to ship this integration while the store is still sold out, but the Shuusou Gyoku OpenGL backend has turned out way too complicated to be finished next to these two pushes within a month. It will take quite a while until the store reopens and you all can start using Stripe, so I'll just link back to this blog post when it happens.

Integrating Stripe wasn't the simplest task in the world either. At first, the Checkout API seems pretty friendly to developers: The entire payment flow is handled on the backend, in the server language of your choice, and requires no frontend JavaScript except for the UI feedback code you choose to write. Your backend API endpoint initiates the Stripe Checkout session, answers with a redirect to Stripe, and Stripe then sends a redirect back to your server if the customer completed the payment. Superficially, this server-based approach seems much more GDPR-friendly than PayPal, because there are no remote scripts to obtain consent for. In reality though, Stripe shares much more potential personal data about your credit card or bank account with a merchant, compared to PayPal's almost bare minimum of necessary data.
It's also rather annoying how the backend has to persist the order form information throughout the entire Checkout session, because it would otherwise be lost if the server restarts while a customer is still busy entering data into Stripe's Checkout form. Compare that to the PayPal JavaScript SDK, which only POSTs back to your server after the customer completed a payment. In Stripe's case, more JavaScript actually only makes the integration harder: If you trigger the initial payment HTTP request from JavaScript, you will have to improvise a bit to avoid the CORS error when redirecting away to a different domain.

But sure, it's all not too bad… for regular orders at least. With subscriptions, however, things get much worse. Unlike PayPal, Stripe kind of wants to stay out of the way of the payment process as much as possible, and just be a wrapper around its supported payment methods. So if customers aren't really meant to register with Stripe, how would they cancel their subscriptions?
Answer: Through the… merchant? Which I quite dislike in principle, because why should you have to trust me to actually cancel your subscription after you requested it? It also means that I probably should add some sort of UI for self-canceling a Stripe subscription, ideally without adding full-blown user accounts. Not that this solves the underlying trust issue, but it's more convenient than contacting me via email or, worse, going through your bank somehow. Here is how my solution works:

• When setting up a Stripe subscription, the server will generate a random ID for authentication. This ID is then used as a salt for a hash of the Stripe subscription ID, linking the two without storing the latter on my server.
• The thank you page, which is parameterized with the Stripe Checkout session ID, will use that ID to retrieve the subscription ID via an API call to Stripe, and display it together with the above salt. This works indefinitely – contrary to what the expiry field in the Checkout session object suggests, Stripe sessions are indeed stored forever. After all, Stripe also displays this session information in a merchant's transaction log with an excessive amount of detail. It might have been better to add my own expiration system to these pages, but this had been taking long enough already. For now, be aware that sharing the link to a Stripe thank you page is equivalent to sharing your subscription cancellation password.
• The salt is then used as the key for a subscription management page. To cancel, you visit this page and enter the Stripe subscription ID to confirm. The server then checks whether the salt and subscription ID pair belong to each other, and sends the actual cancellation request back to Stripe if they do.

I might have gone a bit overboard with the crypto there, but I liked the idea of not storing any of the Stripe session IDs in the server database. It's not like that makes the system more complex anyway, and it's nice to have a separate confirmation step before canceling a subscription.

But even that wasn't everything I had to keep in mind here. Once you switch from test to production mode for the final tests, you'll notice that certain SEPA-based payment providers take their sweet time to process and activate new subscriptions. The Checkout session object even informs you about that, by including a payment status field. Which initially seems just like another field that could indicate hacking attempts, but treating it as such and rejecting any unpaid session can also reject perfectly valid subscriptions. I don't want all this control… 🥲
Instead, all I can do in this case is to tell you about it. In my test, the Stripe dashboard said that it might take days or even weeks for the initial subscription transaction to be confirmed. In such a case, the respective fraction of the cap will unfortunately need to remain red for that entire time.

And that was 1½ pushes just to replicate the basic functionality of a simple PayPal integration with the simplest type of Stripe integration. On the architectural site, all the necessary refactoring work made me finally upgrade my frontend code to TypeScript at least, using the amazing esbuild to handle transpilation inside the server binary. Let's see how long it will now take for me to upgrade to SCSS…

With the new payment options, it makes sense to go for another slight price increase, from up to per push. The amount of taxes I have to pay on this income is slowly becoming significant, and the store has been selling out almost immediately for the last few months anyway. If demand remains at the current level or even increases, I plan to gradually go up to by the end of the year.
📝 As 📝 usual, I'm going to deliver existing orders in the backlog at the value they were originally purchased at. Due to the way the cap has to be calculated, these contributions now appear to have increased in value by a rather awkward 13.33%.

This left ½ of a push for some more work on the TH01 Anniversary Edition. Unfortunately, this was too little time for the grand issue of removing byte-aligned rendering of bigger sprites, which will need some additional blitting performance research. Instead, I went for a bunch of smaller bugfixes:

• ANNIV.EXE now launches ZUNSOFT.COM if MDRV98 wasn't resident before. In hindsight, it's completely obvious why this is the right thing to do: Either you start ANNIV.EXE directly, in which case there's no resident MDRV98 and you haven't seen the ZUN Soft logo, or you have made a single-line edit to GAME.BAT and replaced op with anniv, in which case MDRV98 is resident and you have seen the logo. These are the two reasonable cases to support out of the box. If you are doing anything else, it shouldn't be that hard to adjust though?

  You might be wondering why I didn't just include all code of ZUNSOFT.COM inside ANNIV.EXE together with the rest of the game. The reason: ZUNSOFT.COM has almost nothing in common with regular TH01 code. While the rest of TH01 uses the custom image formats and bad rendering code I documented again and again during its RE process, ZUNSOFT.COM fully relies on master.lib for everything about the bouncing-ball logo animation. Its code is much closer to TH02 in that respect, which suggests that ZUN did in fact write this animation for TH02, and just included the binary in TH01 for consistency when he first sold both games together at Comiket 52. Unlike the 📝 various bad reasons for splitting the PC-98 Touhou games into three main executables, it's still a good idea to split off animations that use a completely different set of rendering and file format functions. Combined with all the BFNT and shape rendering code, ZUNSOFT.COM actually contains even more unique code than OP.EXE, and only slightly less than FUUIN.EXE.

• The optional AUTOEXEC.BAT is now correctly encoded in Shift-JIS instead of accidentally being UTF-8, fixing the previous mojibake in its final ECHO line.

• The command-line option that just adds a stage selection without other debug features (anniv s) now works reliably.

  This one's quite interesting because it only actually ever worked because of a ZUN bug. From a superficial look at the code, it shouldn't, because ZUN forgot to initialize the debug flag inside the resident structure when specifying the s parameter. However, master.lib's resdata_create() function doesn't clear the resident structure after allocation. So if anything on the system previously happened to write something other than 0x00, 0x01, or 0x03 to the debug flag byte, the lack of initialization combined with ZUN actually turns into a distinct non-test and non-debug stage selection mode.
  This is what happens on a certain widely circulated .HDI copy of TH01 that boots MS-DOS 3.30C. On this system, the memory that master.lib will allocate to the TH01 resident structure was previously used by DOS as stack for its kernel, which left the future resident debug flag byte at address 9FF6:0012 at a value of 0x12. This might be the entire reason why game s is even widely documented to trigger a stage selection to begin with – on the widely circulated TH04 .HDI that boots MS-DOS 6.20, or on DOSBox-X, the s parameter doesn't work because both DOS systems leave the resident debug flag byte at 0x00. And since ANNIV.EXE pushes MDRV98 into that area of conventional DOS RAM, anniv s previously didn't work even on MS-DOS 3.30C.

• Both bugs in the 📝 1×1 particle system during the Mima fight have been fixed. These include the off-by-one error that killed off the very first particle on the 80^th frame and left it in VRAM, and, just like every other entity type, a replacement of ZUN's EGC unblitter with the new pixel-perfect and fast one. Until I've rearchitected unblitting as a whole, the particles will now merely rip barely visible 1×1 holes into the sprites they overlap.

• The 📝 score popups for flipped cards are now displayed without the two frames of flicker.

• The bomb value shown in the lowest line of the in-game debug mode output is now right-aligned together with the rest of the values. This ensures that the game always writes a consistent number of characters to TRAM, regardless of the magnitude of the bomb value, preventing the seemingly wrong timer values that appeared in the original game whenever the value of the bomb variable changed to a lower number of digits:

• Finally, I've streamlined VRAM page access changes, which allowed me to consistently replace ZUN's expensive function call with the optimal two inlined x86 instructions. Interestingly, this change alone removed 2 KiB from the binary size, which is almost all of the difference between 📝 the P0234-1 release and this one. Let's see how much longer we can make each new release of ANNIV.EXE smaller than the previous one.

The final point, however, raised the question of what we're now going to do about 📝 a certain issue in the 地獄/Jigoku Bad Ending. ZUN's original expensive way of switching the accessed VRAM page was the main reason behind the lag frames on slower PC-98 systems, and search-replacing the respective function calls would immediately get us to the optimized version shown in that blog post. But is this something we actually want? If we wanted to retain the lag, we could surely preserve that function just for this one instance…
The discovery of this issue predates the clear distinction between bloat, quirks, and bugs, so it makes sense to first classify what this issue even is. The distinction comes all down to observability, which I defined as changes to rendered frames between explicitly defined frame boundaries. That alone would be enough to categorize any cause behind lag frames as bloat, but it can't hurt to be more explicit here.

Therefore, I now officially judge observability in terms of an infinitely fast PC-98 that can instantly render everything between two explicitly defined frames, and will never add additional lag frames. If we plan to port the games to faster architectures that aren't bottlenecked by disappointing blitter chips, this is the only reasonable assumption to make, in my opinion: The minimum system requirements in the games' README files are minimums, after all, not recommendations. Chasing the exact frame drop behavior that ZUN must have experienced during the time he developed these games can only be a guessing game at best, because how can we know which PC-98 model ZUN actually developed the games on? There might even be more than one model, especially when it comes to TH01 which had been in development for at least two years before ZUN first sold it. It's also not like any current PC-98 emulator even claims to emulate the specific timing of any existing model, and I sure hope that nobody expects me to import a bunch of bulky obsolete hardware just to count dropped frames.

That leaves the tearing, where it's much more obvious how it's a bug. On an infinitely fast PC-98, the ドカーン frame would never be visible, and thus falls into the same category as the 📝 two unused animations in the Sariel fight. With only a single unconditional 2-frame delay inside the animation loop, it becomes clear that ZUN intended both frames of the animation to be displayed for 2 frames each:

TH01 Anniversary Edition, version P0239 2023-05-01-th01-anniv.zip

Next up: Taking the oldest still undelivered push and working towards TH04 position independence in preparation for multilingual translations. The Shuusou Gyoku OpenGL backend shouldn't take that much longer either, so I should have lots of stuff coming up in May afterward.

📝 Posted:

2022-08-14 23:17 UTC

🚚 Summary of:

P0214, P0215

⌨ Commits:

158a91e...414770c, 414770c...3123c9d

💰 Funded by:

Ember2528, Yanga

🏷 Tags:

rec98+ th01- animation+ blitting+ score+ card-flipping+ glitch+ rng+ debug-

Last blog post before the 100% completion of TH01! The final parts of REIIDEN.EXE would feel rather out of place in a celebratory blog post, after all. They provided quite a neat summary of the typical technical details that are wrong with this game, and that I now get to mention for one final time:

• The Orb's animation cycle is maybe two frames shorter than it should have been, showing its last sprite for just 1 frame rather than 3:
• The text in the Pause and Continue menus is not quite correctly centered.
• The memory info screen hides quite a bit of information about the .PTN buffers, and obscures even the info that it does show behind misleading labels. The most vital information would have been that ZUN could have easily saved 20% of the memory by using a structure without the unneeded alpha plane… Oh, and the REWIRTE option mapped to the ⬇️ down arrow key simply redraws the info screen. Might be useful after a NODE CHEAK, which replaces the output with its own, but stays within the same input loop.

But hey, there's an error message if you start REIIDEN.EXE without a resident MDRV2 or a correctly prepared resident structure! And even a good, user-friendly one, asking the user to launch the batch file instead. For some reason, this convenience went out of fashion in the later games.

The Game Over animation (how fitting) gives us TH01's final piece of weird sprite blitting code, which seriously manages to include 2 bugs and 3 quirks in under 50 lines of code. In debug mode, you can trigger this effect by pressing the ⬇️ down arrow key, which certainly explains why I encountered seemingly random Game Over events during all the tests I did with this game…
The animation appears to have changed quite a bit during development, to the point that probably even ZUN himself didn't know what he wanted it to look like in the end:

Finally, we get to the big main() function, serving as the duct tape that holds this game together. It may read rather disorganized with all the (actually necessary) assignments and function calls, but the only actual minor issue I've seen there is that you're robbed of any pellet destroy bonus collected on the final frame of the final boss. There is a certain charm in directly nesting the infinite main gameplay loop within the infinite per-life loop within the infinite stage loop. But come on, why is there no fourth scene loop? Instead, the game just starts a new REIIDEN.EXE process before and after a boss fight. With all the wildly mutated global state, that was probably a much saner choice.

The final secrets can be found in the debug mode stage selection. ZUN implemented the prompts using the C standard library's scanf() function, which is the natural choice for quick-and-dirty testing features like this one. However, the C standard library is also complete and utter trash, and so it's not surprising that both of the scanf() calls do… well, probably not what ZUN intended. The guaranteed out-of-bounds memory access in the select_flag route prompt thankfully has no real effect on the game, but it gets really interesting with the 面数 stage prompt.
Back in 2020, I already wrote about 📝 stages 21-24, and how they're loaded from actual data that ZUN shipped with the game. As it now turns out, the code that maps stage IDs to STAGE?.DAT scene numbers contains an explicit branch that maps any (1-based) stage number ≥21 to scene 7. Does this mean that an Extra Stage was indeed planned at some point? That branch seems way too specific to just be meant as a fallback. Maybe Asprey was on to something after all…

However, since ZUN passed the stage ID as a signed integer to scanf(), you can also enter negative numbers. The only place that kind of accidentally checks for them is the aforementioned stage ID → scene mapping, which ensures that (1-based) stages < 5 use the shrine's background image and BGM. With no checks anywhere else, we get a new set of "glitch stages":

The scene loading function takes the entered 0-based stage ID value modulo 5, so these 4 are the only ones that "exist", and lower stage numbers will simply loop around to them. When loading these stages, the function accesses the data in REIIDEN.EXE that lies before the statically allocated 5-element stages-of-scene array, which happens to encompass Borland C++'s locale and exception handling data, as well as a small bit of ZUN's global variables. In particular, the obstacle/card HP on the tile I highlighted in green corresponds to the lowest byte of the 32-bit RNG seed. If it weren't for that and the fact that the obstacles/card HP on the few tiles before are similarly controlled by the x86 segment values of certain initialization function addresses, these glitch stages would be completely deterministic across PC-98 systems, and technically canon…
Stage -4 is the only playable one here as it's the only stage to end up below the 📝 heap corruption limit of 102 stage objects. Completing it loads Stage -3, which crashes with a Divide Error just like it does if it's directly selected. Unsurprisingly, this happens because all 50 card bytes at that memory location are 0, so one division (or in this case, modulo operation) by the number of cards is enough to crash the game.
Stage -5 is modulo'd to 0 and thus loads the first regular stage. The only apparent broken element there is the timer, which is handled by a completely different function that still operates with a (0-based) stage ID value of -5. Completing the stage loads Stage -4, which also crashes, but only because its 61 cards naturally cause the 📝 stack overflow in the flip-in animation for any stage with more than 50 cards.

And that's REIIDEN.EXE, the biggest and most bloated PC-98 Touhou executable, fully decompiled! Next up: Finishing this game with the main menu, and hoping I'll actually pull it off within 24 hours. (If I do, we might all have to thank 32th System, who independently decompiled half of the remaining 14 functions…)

📝 Posted:

2022-08-11 21:27 UTC

🚚 Summary of:

P0212, P0213

⌨ Commits:

d398a94...363fd54, 363fd54...158a91e

💰 Funded by:

LeyDud, Lmocinemod, GhostRiderCog, Ember2528

🏷 Tags:

rec98+ th01- score+ pc98+ performance+ unused+ cutscene+ debug-

Wow, it's been 3 days and I'm already back with an unexpectedly long post about TH01's bonus point screens? 3 days used to take much longer in my previous projects…

Before I talk about graphics for the rest of this post, let's start with the exact calculations for both bonuses. Touhou Wiki already got these right, but it still makes sense to provide them here, in a format that allows you to cross-reference them with the source code more easily. For the card-flipping stage bonus:

The boss stage bonus is calculated from the exact same metrics, despite half of them being labeled differently. The only actual differences are in the higher multipliers and in the cap for the stage number bonus. Why remove it if raising it high enough also effectively disables it?

The transition between the gameplay and TOTLE screens is one of the more impressive effects showcased in this game, especially due to how wavy it often tends to look. Aside from the palette interpolation (which is, by the way, the first time ZUN wrote a correct interpolation algorithm between two 4-bit palettes), the core of the effect is quite simple. With the TOTLE image blitted to VRAM page 1:

• Shift the contents of a line on VRAM page 0 by 32 pixels, alternating the shift direction between right edge → left edge (even Y values) and the other way round (odd Y values)
• Keep a cursor for the destination pixels on VRAM page 1 for every line, starting at the respective opposite edge
• Blit the 32 pixels at the VRAM page 1 cursor to the newly freed 32 pixels on VRAM page 0, and advance the cursor towards the other edge
• Successive line shifts will then include these newly blitted 32 pixels as well
• Repeat (640 / 32) = 20 times, after which all new pixels will be in their intended place

So it's really more like two interlaced shift effects with opposite directions, starting on different scanlines. No trigonometry involved at all.

Horizontally scrolling pixels on a single VRAM page remains one of the few 📝 appropriate uses of the EGC in a fullscreen 640×400 PC-98 game, regardless of the copied block size. The few inter-page copies in this effect are also reasonable: With 8 new lines starting on each effect frame, up to (8 × 20) = 160 lines are transferred at any given time, resulting in a maximum of (160 × 2 × 2) = 640 VRAM page switches per frame for the newly transferred pixels. Not that frame rate matters in this situation to begin with though, as the game is doing nothing else while playing this effect.
What does sort of matter: Why 32 pixels every 2 frames, instead of 16 pixels on every frame? There's no performance difference between doing one half of the work in one frame, or two halves of the work in two frames. It's not like the overhead of another loop has a serious impact here, especially with the PC-98 VRAM being said to have rather high latencies. 32 pixels over 2 frames is also harder to code, so ZUN must have done it on purpose. Guess he really wanted to go for that 📽 cinematic 30 FPS look 📽 here…

Once all the metrics have been calculated, ZUN animates each value with a rather fancy left-to-right typing effect. As 16×16 images that use a single bright-red color, these numbers would be perfect candidates for gaiji… except that ZUN wanted to render them at the more natural Y positions of the labels inside CLEAR3.GRP that are far from aligned to the 8×16 text RAM grid. Not having been in the mood for hardcoding another set of monochrome sprites as C arrays that day, ZUN made the still reasonable choice of storing the image data for these numbers in the single-color .GRC form– yeah, no, of course he once again chose the .PTN hammer, and its 📝 16×16 "quarter" wrapper functions around nominal 32×32 sprites.

Why do I bring up such a detail? What's actually going on there is that ZUN loops through and blits each digit from 0 to 9, and then continues the loop with "digit" numbers from 10 to 19, stopping before the number whose ones digit equals the one that should stay on screen. No problem with that in theory, and the .PTN sprite selection is correct… but the .PTN quarter selection isn't, as ZUN wrote (digit % 4) instead of the correct ((digit % 10) % 4). Since .PTN quarters are indexed in a row-major way, the 10-19 part of the loop thus ends up blitting 2 → 3 → 0 → 1 → 6 → 7 → 4 → 5 → (nothing):

Seriously though? If the deadline is looming and you've got to rush some part of your game, a standalone screen that doesn't affect anything is the best place to pick. At 4 milliseconds per digit, the animation goes by so fast that this quirk might even add to its perceived fanciness. It's exactly the reason why I've always been rather careful with labeling such quirks as "bugs". And in the end, the code does perform one more blitting call after the loop to make sure that the correct digit remains on screen.

Lovely! With no mouse-related code left in the game otherwise, this cursor sprite provides some great fuel for wild fan theories about TH01's development history:

1. Could ZUN have 📝 stolen the basic PC-98 VSync or text RAM function code from a source that also implemented mouse support?
2. Did he have a mouse-controlled level editor during development? It's highly likely that he had something, given all the 📝 bit twiddling seen in the STAGE?.DAT format.
3. Or was this game actually meant to have mouse-controllable portions at some point during development? Even if it would have just been the menus.

… Actually, you know what, with all shared data moved to C land, I might as well finish FUUIN.EXE right now. The last secret hidden in its main() function: Just like GAME.BAT supports launching the game in a debug mode from the DOS command line, FUUIN.EXE can directly launch one of the game's endings. As long as the MDRV2 driver is installed, you can enter fuuin t1 for the 魔界/Makai Good Ending, or fuuin t for 地獄/Jigoku Good Ending.
Unfortunately, the command-line parameter can only control the route. Choosing between a Good or Bad Ending is still done exclusively through TH01's resident structure, and the continues_per_scene array in particular. But if you pre-allocate that structure somehow and set one of the members to a nonzero value, it would work. Trainers, anyone?

Alright, gotta get back to the code if I want to have any chance of finishing this game before the 15^th… Next up: The final 17 functions in REIIDEN.EXE that tie everything together and add some more debug features on top.