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re(ui): rotation is not nested-only, and the pivot-anchored scale is measured

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Two corrections and one new confirmation, all from finishing the sweep I
left running last iteration.

Refuted, by my own sweep, within the hour: "rotation appears to live only
in nested .rat leaf records". That held for GP_TITLE, GP_BUNK and
GP_CHALLENGE -- the three archives the sweep had reached when I wrote it
-- and fails on GP_DIALOG and GP_DEBRIEFING_PILOTLOG, which rotate
top-level elements. Scoping the claim made it cheap to withdraw, but the
sentence should have waited for the sweep.

Those top-level cases are the best evidence on the disc, and they show up
in `screen info --geometry` without a hex dump. GP_DIALOG build 0:
pceff03/pceff04 ramp r = 90 -> 30 -> 10 -> 3 -> 0 while alpha ramps
0 -> 255 and they slide into place -- a swing-in settling upright. Build
6: pzeff02 ramps 43 -> 61 -> 75 -> 90 while scaling 112% -> 200% and
fading to 0 -- a spin-out. Rows committed as reference data.

New: the pivot-anchored scale term in blit, kf.x - pivot*(scale-100)/100,
was implemented and reasoned about but never measured, because every
element previously examined sits at 100% scale where the term is exactly
zero. The ptloop pair scale 600% and 800%, where it is worth 450 and 630
px. Formula predicts centre y = 360.0 for both; capture measures 359.1
and 360.0. Top-left anchoring predicts 810 and 990. Horizontally it makes
t-from-position agree with t-from-alpha to 0.33 / 0.65 units against ~8
without it.

That agreement does NOT prove linear interpolation -- both fields were
inverted through the same linear map, so a shared easing curve cancels.
It shows position and alpha ride one shared parameter. Recorded as such.

The disc-wide sweep is still running; the count is incomplete, the
existence is settled.
This commit is contained in:
Sylpheed RE agent
2026-08-28 22:46:44 +00:00
parent ffd1a30ba7
commit f5097779e4
5 changed files with 124 additions and 15 deletions
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77
docs/re/structures/ui-keyframe-rotation.md
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@@ -78,6 +78,65 @@ full-turn ramp that changes nothing else is a spin in place; no non-rotation
reading of the field explains it. Disc-wide, `360` occurs 1 173 times and `−360`
180 times.
## ✅ The strongest evidence is `GP_DIALOG`, and it is visible in the CLI
`sylpheed-cli screen info --build 0 --geometry dat/GP_DIALOG.pak`. These are
**top-level** elements, so no hex dump is needed to see them:
| element | `+12` across the group | what else moves |
|---|---|---|
| `pceff03.t32` | **90 → 30 → 10 → 3 → 0** | alpha 0 → 128 → 192 → 224 → 255; position slides (630,348) → (470,198) |
| `pceff04.t32` | **90 → 30 → 10 → 3 → 0** | the same ramp, mirrored path (413,77) → (553,247) |
| `pzeff02.t32` (build 6) | **43 → 61 → 75 → 90** | scale 112 % → 200 %, alpha 255 → 0 |
The first two are a swing-in that *decays to zero exactly as the element
settles*; the third is a burst that spins as it expands and fades. A monotone
decay to 0 synchronised with a fade-in, and a spin-out synchronised with an
expanding fade-out, are what a rotation field does and are not what any other
reading of the word would produce.
`GP_DEBRIEFING_PILOTLOG` build 10 holds the static case: `pjeff24a.t32`, one
keyframe, `r=90` at 210 % scale.
These four rows are committed verbatim at
[`data/rotation-top-level-examples.txt`](../data/rotation-top-level-examples.txt).
⚠️ The sweep that found them — every build of every `GP_*.pak`, grepped for a
non-zero `r=` — **had not finished** at the time of writing; it was in
`GP_DIALOG` build 37 with two archives hit so far. Treat the *count* as
incomplete and the *existence* as settled.
## ✅ Bonus, from the same two quads: the pivot-anchored scale is measured-correct
`ui_layout::blit` places a scaled element as
`ox = kf.x − pivot·(scale−100)/100`, keeping the **pivot** fixed rather than the
top-left. That was implemented and reasoned about, never measured — and until now
there was nothing to measure it against, because the title's other elements are
all at 100 % scale where the term vanishes. The `ptloop` pair scale **600 %** and
**800 %** vertically, so the term is worth 450 and 630 px:
| element | measured centre Y | pivot-anchored | top-left | position-as-centre |
|---|---|---|---|---|
| `ptloop01` (600 %) | **359.1** | **360.0** ✅ | 810.0 | 270.0 |
| `ptloop02` (800 %) | **360.0** | **360.0** ✅ | 990.0 | 270.0 |
Two different scales, both landing on 360.0. Horizontally the same term is worth
199.5 px, and there is an independent cross-check available: solve the group's
`t` from the quad's **position**, then from its **vertex alpha**, and see whether
the two agree.
| element | | t from position | t from alpha | Δ |
|---|---|---|---|---|
| `ptloop01` | with the pivot term | 571.98 | 571.65 | **0.33** |
| | without | 579.65 | 571.65 | 8.00 |
| `ptloop02` | with the pivot term | 668.92 | 668.27 | **0.65** |
| | without | 659.71 | 668.27 | 8.55 |
🟡 **What this does *not* show is that interpolation is linear.** Both fields
were inverted through the same linear map, so a shared easing curve would cancel
out and still agree. What it does show is that position and alpha are driven off
**one shared parameter** — which is worth knowing on its own, and is why the
agreement is a real check on the placement formula rather than a tautology.
## Disc-wide census
[`tools/re-capture/kf_rotation_census.py`](../../../tools/re-capture/kf_rotation_census.py),
@@ -102,15 +161,15 @@ expressed in degrees rather than of a free angle. 🟡 That is a hypothesis abou
rotated element upright. Rotating the blit is a real change to the compositor
and was not attempted here. **The title render's residual band is expected to
persist until it is.**
* 🟡 **Rotation appears to live only in nested `.rat` leaf records.** Every
instance located so far — the two `ptloop` records, the `GP_BUNK` spin — is
nested, and `screen info --geometry`'s new `r=` column is empty on every build
of `GP_TITLE`, `GP_BUNK` and `GP_CHALLENGE` (the CLI lists the top-level
declaration table only). **A full sweep of every build on the disc has not
finished**, so this is a pattern across three archives, not a disc-wide
negative. It is stated because it matters to a consumer either way: a composer
that reads only the declaration table will see no rotation on the elements that
actually rotate.
* 🔴 ~~"Rotation appears to live only in nested `.rat` leaf records."~~
**Refuted by my own sweep, within the hour.** It held for `GP_TITLE`,
`GP_BUNK` and `GP_CHALLENGE` — the three archives I had checked when I wrote
it — and fails on the very next one: `GP_DIALOG` and
`GP_DEBRIEFING_PILOTLOG` carry rotation on **top-level** elements, and those
are the best evidence on the disc (below). Rotation lives in both places.
The half that survives is the one that matters to a consumer: a composer that
reads only the declaration table will miss the *title's* rotations, because
those particular ones are nested.
* **The blocks are not 4-byte aligned.** A nested `RATC` blob can start at an odd
offset (`ptloop01.rat` at `0xbb5966`), and its blocks inherit that. Any scanner
over raw bundle bytes must not assume alignment — see