6f4ba93c5c
Records the settle-time decode, and corrects two claims it overturns.
docs/re/structures/ui-settle-time.md is the finding: a settled screen is one
instant every element is posed at, the disc names it (the midpoint of the
longest keyframe-free interval), and the title's arc closes from 33.22 to
11.79 with the clipped-pixel count landing on the console's 1459 within 0.5%.
Includes the disc-wide reach -- only 30% of bundles have a window wide enough
to trust -- and a three-way figure.
Withdrawn in ui-rotation-implemented.md:
* "Flat. No minimum." was not a property of rotation. `at` posed LEAVES ONLY,
so the scan moved the light sweeps and never touched the top-level flashes.
* "our renderer does not draw ptlogo1/ptlogo2 at all" is wrong. Both are
drawn; the four elements the diagnostic named are kind-0x4 ghosts sharing
their template's name. Hiding the real ones makes the error WORSE by
+5.20 and +7.47.
* Its 10.92 baseline is not reproducible -- 14.07 at its own pre-change tag
and 14.07 today -- so the "1.7% better" verdict rests on an unrecorded
recipe. Flagged in title-residual-tone-vs-geometry.md too.
METHOD.md gains two traps: a shared CARGO_TARGET_DIR makes a `git worktree`
build silently replace the binary you run next (it cost three renders here,
caught only because a missing flag was a hard error rather than a wrong
number); and an aggregate computed per-element is not a state of the system.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QsEPXWVaEpyfudtR6re1Pd
154 lines
7.6 KiB
Markdown
154 lines
7.6 KiB
Markdown
# The settled screen is one instant, not one hold per element
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**Classification: decoded.** The value comes from the keyframe table alone —
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no capture is consulted to compute it — and it is checked disc-wide. The
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verification against the console capture is a *test* of the decode, not its
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source.
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## The claim
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`Element::rest()` returns an element's last **hold** keyframe, chosen for that
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element independently of every other element. A composite built from `rest()` is
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therefore not a screen at any moment in time; it is a per-element maximum.
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For an element that ends the screen settled, that is the same thing. For a
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**transient** it is exactly wrong — a flash's last hold *is* the flash peak, so
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`rest()` leaves it burning forever.
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The settled screen is instead **one instant that every element is posed at**, and
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the disc says which instant: gather every keyframe time in the build and take the
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**longest interval containing none of them**. Inside that gap nothing has an
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inflection, so every element is either holding or midway along a single linear
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ramp. That is what "the screen has stopped changing" means, expressed in the only
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vocabulary the file has.
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`UiBuild::settle_time()` returns the midpoint of that interval;
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`UiBuild::settle_window()` returns the interval, whose width is how much
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confidence the midpoint deserves.
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## The case that found it
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`GP_TITLE` build 4. Seven elements share the light-arc band behind the logo:
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| element | timeline | at rest | at t=198 |
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|---|---|---|---|
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| `ptlogo_back2eff1.t32` | a=0 → **255 at t54–56** → 0 by t58 | **255** | 0 |
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| `ptlogo_back2eff2.t32` | a=0 → **255 at t58–60** → 0 by t62 | **255** | 0 |
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| `ptlogo_back2eff3.t32` | staggered, same shape | **255** | 0 |
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| `ptlogo_back2eff4.t32` | staggered, same shape | **255** | 0 |
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| `ptlogo_back2eff5.t32` | 255 at t64–66 → 192 at t74 → **0 by t110** | **255** | 0 |
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| `ptlogo_back2eff.t32` | 255 at t66, **holds to t238**, exits t244 | 255 | 255 |
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| `ptlogo_back2.t32` | 255 at t80, **holds to t243**, exits t249 | 255 | 255 |
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The five numbered ones are a single light sweep travelling left to right across
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the logo, drawn as five staggered two-frame flashes. They are all extinguished by
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t110. `rest()` draws them **simultaneously and permanently**, and five stacked
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white glows (`ptlogo_back2eff5.t32` decodes to a mean opaque RGB of exactly
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255,255,255) drive the arc to saturation.
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## What it looks like
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The console's arc is a **thin white outline with a pink hooked tail**. `rest()`
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renders a fat solid white blob that swallows the tail completely — five white
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glows stacked. `--settle` reproduces the console.
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⚠️ A measurement trap worth recording: sampling the *brightest 3 %* of that band
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gives (252,245,239) for the console against (255,255,255) for `rest()` — nearly
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neutral, and it reads as "no hue difference". That statistic samples the white
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outline in both and never touches the pink tail. What it *did* expose was the
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count: at a 97th-percentile threshold the console has 1 459 pixels above it and
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`rest()` has 8 581, i.e. a saturated plateau. **The pixel count carried the
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signal that the mean colour hid.**
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## The measurement
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Against
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[`live-title-build4-no-plate.png`](../captures/title-builds/live-title-build4-no-plate.png),
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whole frame and over the arc band (y 95–215, x 830–1230). The third column counts
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pixels at or above the band's 97th-percentile luminance — a *saturation* statistic,
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independent of the error being minimised, and not fitted.
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| | mean abs diff | arc band | clipped px |
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|---|---|---|---|
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| **console capture** | — | — | **1 459** |
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| `rest()` — the default | 14.07 | 33.22 | 8 581 |
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| **`--at 198` — predicted from the disc** | **12.06** | **11.79** | **1 452** |
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| `--at 100` — control, before the window | 19.13 | 20.46 | 1 468 |
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| `--at 358` — control, past every exit | 28.80 | 53.37 | 1 447 |
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**t=198 was computed before the render was scored.** `settle_window()` on build 4
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returns `[160, 236]`; 198 is its midpoint. A separate sweep of t in 40…300 finds a
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flat optimum over t ∈ [180, 238] at 12.06 / 11.79 / 1 452, which contains the
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prediction.
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⚠️ The clipped-pixel count discriminates `rest()` from *any* single instant — the
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two controls also land near 1 459 — so it identifies the **blow-out**, not the
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time. The time is identified by the mean, and by the disc.
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## The controls
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* ✅ **`at = None` is byte-identical.** `compose` with no `at` produces the same
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bytes before and after this change (`cmp`, exact). The default path is untouched.
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* ✅ **The change did not regress the resting composite.** Rendering build 4 at
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`formats-pin-2026-08-29c` (pre-rotation, pre-leaf) and at the current tree both
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give **14.07 / 33.22**.
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* ✅ **A hand-picked visibility list reaches the same answer.** Leave-one-out over
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all 24 elements, then hiding exactly `eff1`…`eff5` and keeping the two holders,
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gives 12.06 / 11.79 / 1 452 — identical to `--at 198`. The principled rule
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reproduces the hand-picked one with nothing hand-picked.
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* ✅ **Disc-wide self-consistency.** For every bundle with a window, no element has
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a keyframe strictly inside it, and the midpoint lies within it —
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`tests/ui_settle_time_disc.rs`.
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## 🔴 Reach: this does not apply to every bundle
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Of the **1 758** composable bundles carrying two or more keyframe times:
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| | count | share |
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|---|---|---|
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| settle window ≥ 30 units (0.5 s) | 524 | 30 % |
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| settle window < 10 units | 731 | 42 % |
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| mean window | 49 units | — |
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The 42 % are mostly `loop*` animation fragments, which are **meant** to be in
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motion and have no settled pose to find. **Check the window width before trusting
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the midpoint.** A narrow window is the data saying "this bundle never settles",
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not a settle time with a small error bar.
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## What this corrects elsewhere in the corpus
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* 🔴 [`ui-rotation-implemented.md`](ui-rotation-implemented.md) records the pose
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scan as **"Flat. No minimum."** over t = 0…600. The cause is now known:
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`ComposeOptions::at` was posing **leaves only**, so the scan moved the light
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sweeps and never touched the top-level flashes. No `t` could have helped. `at`
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now poses every element.
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* 🔴 The same document blames the residual on our renderer **"not drawing
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`ptlogo1` / `ptlogo2` at all (four elements)"**. That is **withdrawn**. Build 4
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declares *six* ptlogo elements: indices 0 and 1 are kind `0x0` at (184,193) and
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(137,308), alpha 255, and are **drawn**; indices 2–5 are kind `0x4` ghost
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instances at (−116,−7) and (437,508), alpha 0, and are skipped deliberately.
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Hiding element 0 makes the error **worse** by +5.20 whole-frame and +7.61 in the
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band; element 1 by +7.47. They are drawn and correctly placed.
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* ❔ The **10.92** baseline in that document's table is **not reproducible**.
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`screen render --build 4 --black` against that capture gives 14.07 at the
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pre-change tag and 14.07 now. Some element of that recipe was not recorded.
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Conclusions resting on 10.92 — including the "1.7 % better" verdict on rotation
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— should be treated as unverified until the recipe is recovered.
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## What is not settled
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❔ The remaining **12.06**. It is broad and level-like rather than localised,
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which is consistent with the tone term that
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[`title-residual-tone-vs-geometry.md`](title-residual-tone-vs-geometry.md)
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measures. The arc band is no longer where the error lives.
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## Reproducing
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```bash
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cargo run -q -p sylpheed-cli -- screen render --build 4 --black --at 198 \
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"$SYLPHEED_DISC/dat/GP_TITLE.pak" /tmp/title.png
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SYLPHEED_DISC=/disc cargo test -p sylpheed-formats --test ui_settle_time_disc
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```
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