53f834562a
Partly closes ui-prm-primitives.md's standing blocker, "where an UNMEASURED
primitive paints". Raised by the port: build_12/build_15 composite to solid
black at every instant of their declared life, because pgloading_eff00.prm -- a
full-screen opaque quad -- sorts last.
The rule is a constraint read off the file, not a preference: an element that
covers the screen and is fully opaque at some instant cannot paint above
anything visible at that instant. Where the elements visible during its opaque
span are ALL of them, its position is forced to first.
pgloading_eff00.prm is opaque for 39 instants and all 9 other elements are
visible inside that span -> forced first, 4/4 instances.
Two controls, both measured orders from the running game, and the rule has to
survive both:
* palogo_eff0.prm is measured painting FIRST -- opaque 211 instants, forced
below 6 of 6. It is NAMED like an overlay, so a name-based rule sorts it
wrong against a measured order. Occlusion gets it right.
* pteff00.prm is measured painting LAST -- opaque for 2 instants at its
screen's entry and exit, forced below only 3 of 23, so the constraint
permits it on top where it belongs.
Disc-wide: 80 instances forced first, 50 constrained but not forced, 0
unconstrained. The split runs almost exactly along the names -- every *base* is
forced, every *eff00* is not -- with three families crossing it, which is
exactly why the name is not the rule.
It also explains 36 builds the corpus had recorded as "coming out one colour"
with no cause: pzeff00.prm is forced first in 32 of 32 instances, so they were
wiped by our own sort rather than by the game.
The rule's real limit was found by its own disc-wide test failing. Applied to
any element it claimed 22 .t32 SPRITES must sort first against their own layer
keys -- pneff01.t32 (key 0xd850, #8 of 13) and pbfriendly.t32 (0x9230, #17 of
49). A sprite's ELEMENT alpha says nothing about whether its TEXTURE covers the
screen, so forced_backdrop is now restricted to untextured primitives, which is
also the only case derived_paint_order consults it for.
Reach stated: assumes straight alpha-over (blend mode is still open, and an
additive quad at alpha 255 would not occlude); it is a lower bound, not an
ordering; and there is no new oracle measurement -- both controls are prior
ones, and a loading screen is not reachable from the title path.
3 new disc tests; the 13 paint-order tests are green, including
the_derived_order_matches_the_measured_ones_up_to_ties.
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.