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re(ui): kill two candidate meanings for the T8aD 0x02 bit, and fix attribution

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The bit at +0x04 was recorded as a real field with its meaning "not
diagnosed", noting ptlogo_back2eff is 0x8830 "despite its name". That note
rested on a size match -- and its size is ambiguous, which is the trap
this corpus already records.

First, a sound attribution. T8aD headers appear in the bundle in RATC
CHILD ORDER, verified on GP_TITLE build 4 against an independent property
-- each header's decoded dimensions versus the dimensions the named child
should have: 18 of 18 match, 0 mismatches. Two of those eighteen share a
size (ptlogo_back2eff and ptlogo_back2eff5, both 1133x280), so a size-keyed
lookup cannot separate them; ordering can. Index 12 is back2eff5 (0x8832,
bit set), index 14 is back2eff (0x8830, bit clear). The documented
counterexample is real and correctly attributed -- now on evidence.

Two candidate meanings tested and refuted:

  bit <=> name contains "eff"        REFUTED: ptlogo_back2eff is an eff
                                     name with the bit clear. All 10
                                     bit-set sprites are eff names, so
                                     the implication holds one way only.
  bit <=> the element is transient   REFUTED: pteff03/pteff03a carry the
                                     bit and run to t=250, ramping to
                                     a=255 and holding.

Up close, the exception pair differs in two header words: +0x04
0x8832/0x8830 and +0x08 0x8083/0x8081 -- layer keys 32899 and 32897. They
are NOT duplicates: their alpha summaries agree to one decimal (4.5%
opaque, 86.7% clear, mean 19.3) but a pixel compare gives max abs diff 21.
Two renditions of one image at one size, which is why the summaries were
not trusted.

Still not diagnosed, and said so -- but the search space is two smaller
and the attribution beneath it is now sound.

METHOD: T8aD headers sit in child order, use that not the size; and
identical summary statistics are not identical data.
This commit is contained in:
Sylpheed RE agent
2026-08-29 03:14:40 +00:00
parent c463f98164
commit 5f701db588
4 changed files with 75 additions and 1 deletions
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53
docs/re/structures/ui-paint-order-key.md
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@@ -496,3 +496,56 @@ carries the word as `flags`, documented and *not* acted on.
Worth noting `ptlogo_back2eff` carries `0x8830` **despite** having `eff` in its
name — so the split is the field's, not a naming pattern's. What the bit *does*
mean is still unknown.
---
## 🟡 The `+0x04` bit `0x02`: two candidate meanings killed, attribution now sound
**2026-08-29.** This page recorded the bit as a real independent field
(set in 27.1 % of 19 216 sprites) with its "additive blend" reading refuted and
its meaning ❔ *not diagnosed*, noting that `ptlogo_back2eff` is `0x8830`
"despite its name". Two things here: that note rested on a **size match**, and
the size is ambiguous.
### ✅ First, a sound way to attribute a header to a name
`T8aD` headers appear in the bundle **in RATC child order**. Verified on
`GP_TITLE` build 4 by an independent property — each header's decoded
dimensions against the dimensions the named child should have:
**18 of 18 match, 0 mismatches.**
That matters because two of the eighteen share a size (`ptlogo_back2eff` and
`ptlogo_back2eff5`, both 1133×280), so a size-keyed lookup cannot tell them
apart — the trap [METHOD.md](../METHOD.md) already records for this corpus.
Ordering resolves them: index 12 is `ptlogo_back2eff5` (`0x8832`, bit **set**),
index 14 is `ptlogo_back2eff` (`0x8830`, bit **clear**).
So the documented counterexample is **real and correctly attributed** — now on
evidence rather than on a guess between two same-sized sprites.
### 🔴 Two candidate meanings, both refuted
| hypothesis | verdict |
|---|---|
| bit ⟺ the name contains `eff` | **refuted** — `ptlogo_back2eff` is an `eff` name with the bit clear. All 10 bit-set sprites *are* `eff` names, so the implication holds one way only |
| bit ⟺ the element is transient (gone before the screen settles) | **refuted** — `pteff03`/`pteff03a` carry the bit and run to `t=250`, ramping to `a=255` and holding, i.e. they persist |
### 🟡 What the exception looks like up close
`ptlogo_back2eff` and `ptlogo_back2eff5` are the same size and the same artwork,
and differ in **two** header words:
```
ptlogo_back2eff5 +0x04 00008832 +0x08 00008083 (layer key 32899, bit SET)
ptlogo_back2eff +0x04 00008830 +0x08 00008081 (layer key 32897, bit clear)
```
⚠️ They are **not** duplicates: pixel-compared, `max abs diff 21`. Their alpha
summaries are identical to one decimal (4.5 % opaque, 86.7 % clear, mean 19.3),
which is precisely why the summaries were not trusted — two different renditions
of one image at one size.
So the bit tracks something that also distinguishes two versions of the same
artwork, alongside a different layer key. ❔ **Still not diagnosed**, but the
search space is smaller by two and the attribution underneath it is now sound.