cb084e0a39
A disc-wide census of the ARGB that keyless elements carry. Every full-screen *eff00* PRIMITIVE is pure black at its various alphas (ff000000, 7f000000, 40000000, b2000000, cc000000, d4000000, 00000000). Black at alpha a over content is exactly an alpha-over dim or fade, and an additive black quad would be a no-op nobody would author -- so this narrows the open blend question a long way. The only non-black primitive on the disc is pbafc.prm, RGB 00e8e0 cyan at alphas up to ff, and it is 844x600, NOT full-screen, so it sits outside forced_backdrop's geometry guard. It is now the sole additive candidate. The census also refutes my own argument for nearly half its verdicts. Of the 80 forced-first instances only 42 are .prm; 38 are .tbm carrying fade ffffffff. A SOLID white quad at alpha 255 painted first would make the screen white, and no screen is white -- so a .tbm is a white modulation on a texture, and element alpha does not establish its coverage. That is the .t32 error one file extension further out. I guarded that with el.sprite.is_some(), which fixed the symptom and not the cause: an element's alpha is not its texture's opacity, and only an untextured primitive makes the two the same fact. So 42 verdicts stay decoded and 38 drop to inferred -- still almost certainly right, since all are named *base*, all are full-screen, and pfbase.tbm's first position is measured in the running game, but that is a name-and-role argument which this page elsewhere calls the weaker kind. The code is deliberately unchanged. Restricting forced_backdrop to .prm would send eleven screens' backgrounds back to u32::MAX -- last -- which is the blank-screen bug the rule was written to fix. Downgrading the status is honest; reverting the position would be wrong. The 42/38 split is pinned by a test so anyone tightening the rule sees what it costs. Separately, on the port's black_hold_units ask: four more no-input boots yielded one usable log, which armed late and missed the publisher splash, so the sample is still two runs spanning 3 and 4 frames. Their 6.5-9.2 range stands. And a reason it may not be resolvable this way: the draw log DROPS frame numbers -- in the 3-frame run, frames 121 and 124 are absent entirely, so "frames with no sprite" and "span of frame numbers" are different quantities. Their statistical correction is taken: at n=3 the sample SD (3.893) is the estimator, not the population SD (3.179), making my run 1.88 sigma from the corpus mean rather than 2.31. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01QsEPXWVaEpyfudtR6re1Pd
Reverse-engineering knowledge base
This directory is the spec-side of the clean-room: it records what the original Project Sylpheed binary does (behaviour) and how its data is laid out, so that the Rust port can be implemented from these specs without re-deriving anything and without ever copying original code.
It exists to answer one question fast: "do we already know how X works, and how sure are we?"
The one rule that matters
Never document a claim more confidently than the evidence supports, and never paste original code here.
A wrong-but-confident note is worse than no note: someone builds on it and the bug hides for weeks. Every entry therefore carries an explicit confidence and its evidence. This mirrors the project method — measure the oracle, never infer; refute before believing.
Clean-room firewall
- ✅ Allowed: behaviour descriptions, field offsets/types, formulas, state machines,
observed input→output pairs, and references to the original by address
(
sub_821B68C0) or toxenia-rs/sylpheed.db. - ❌ Forbidden here and in
crates/: pasted decompiled C/C++ or verbatim disassembled function bodies presented as the thing to reimplement. Cite the address; describe the behaviour in your own words. Disassembly is a tool for understanding, not a source to copy.
Confidence levels
| Level | Meaning | Bar to reach it |
|---|---|---|
CONFIRMED |
Behaviour verified against ground truth. | ≥2 independent observations or one observation cross-checked against an oracle (canary framebuffer, a known-correct value, a second code path). |
PROBABLE |
Strong single-source inference. | One clean observation, or an unambiguous static read of the disassembly. |
HYPOTHESIS |
Educated guess, not yet tested. | Anything else. Must say what would confirm/refute it. |
The status markers
The table above is the confidence scale. The markers that appear in
BACKLOG.md and the structures/ pages are a separate, and until now undefined,
vocabulary. They mean:
| Marker | Meaning |
|---|---|
| ✅ | Confirmed — verified against ground truth. |
| 🟡 | Partial: true as far as it goes, or true under a stated assumption. |
| ❔ | Open question. Nobody has answered it yet. |
| 🔴 | Refuted — shown false — or blocked by something the container cannot do. |
| ❌ | A specific claim that was tried and failed. Prefer 🔴. |
| 🚧 | Work started and not finished. |
🔴 never means "we have not run it yet." That is ❔ or 🚧. Reserve 🔴's "blocked" sense for a real limit of the box — no push credentials, no hardware Vulkan (lavapipe only), or a decision only the user can make. The box can run the emulator, script input, screenshot, read guest memory, and build and test Rust, so "needs a run" is never a blocker. This paragraph exists because the marker was undefined for 98 uses and three of them were mislabelled that way.
Promotion requires new evidence, not re-reading the old evidence. A HYPOTHESIS that
"looks right again" is still a HYPOTHESIS. Only an independent check promotes it.
If evidence later contradicts an entry, demote it and record the contradiction — do
not silently edit the conclusion.
When to document
- Right after a function/structure crosses from
HYPOTHESISto at leastPROBABLE— before moving to the next code path, so the knowledge isn't lost or re-derived. - Whenever confidence changes (up or down) — append to the Evidence log, don't overwrite.
- Not while it's still a pure guess with no evidence — a one-liner in the relevant backlog/plan is enough until there's something to stand on.
What to document
- Functions/code paths →
docs/re/functions/<name>.md(one file per function or tight cluster). - Data structures / formats →
docs/re/structures/<name>.md. - Keep the index in
INDEX.md(one line each: name · confidence · one-line summary).
Use the templates: _TEMPLATE.function.md,
_TEMPLATE.structure.md.
How we find and confirm code paths (the toolchain)
Everything joins on the guest virtual address (PC) — code addresses are fixed by the XEX load, identical across our emulator and canary.
- Static (cheap, try first):
xenia-rs/sylpheed.db(DuckDB: 25 481 functions, xrefs, strings, vtables, imports). Query withxenia-rs/zq.py—zq.py grep <str>,zq.py xref <addr>,zq.py dis <lo> <hi>,zq.py fn <pc>. Entry points are usually a string (zq.py grep MSG_DEMO) or an import (movie/XMA API) xref'd back to the loader. - Dynamic (when static is ambiguous): run
xenia-rswith its probe suite —--pc-probe/--audit-pc-probe-hex(fires at block entry),--mem-watch(mid-block reads/writes of a VA),--lr-trace(call/return chains),--trace-instructions,--dump-addr(read guest memory). These already exist; prefer them over hacking canary. - Oracle (correctness ground truth): canary — the Wine cross-build
xenia-canary/build-cross/bin/Windows/Debug/xenia_canary.exe(the native Linux ELF crashes / does not run — do not use it). This is the only emulator that reaches the in-game menu; ourxenia-rsnever got past the intro video. Use canary to observe output (capture its framebuffer for texture colours), not usually to instrument code — though itsbuild-crosstoolchain does compile, so small C++ probes + rebuild are possible when needed. Run muted, one emulator process at a time, point it at the real ISO (not the symlink).
⚠️ VA-equality caveat: join code by PC (fixed), but never assume a data VA holds the same bytes across emulators — allocators differ. Compare data by content/layout.