# The settled screen is one instant, not one hold per element

**Classification: decoded.** The value comes from the keyframe table alone —
no capture is consulted to compute it — and it is checked disc-wide. The
verification against the console capture is a *test* of the decode, not its
source.

## The claim

`Element::rest()` returns an element's last **hold** keyframe, chosen for that
element independently of every other element. A composite built from `rest()` is
therefore not a screen at any moment in time; it is a per-element maximum.

For an element that ends the screen settled, that is the same thing. For a
**transient** it is exactly wrong — a flash's last hold *is* the flash peak, so
`rest()` leaves it burning forever.

The settled screen is instead **one instant that every element is posed at**, and
the disc says which instant: gather every keyframe time in the build and take the
**longest interval containing none of them**. Inside that gap nothing has an
inflection, so every element is either holding or midway along a single linear
ramp. That is what "the screen has stopped changing" means, expressed in the only
vocabulary the file has.

`UiBuild::settle_time()` returns the midpoint of that interval;
`UiBuild::settle_window()` returns the interval, whose width is how much
confidence the midpoint deserves.

🔴 **Gather the times from the TOP-LEVEL elements only — not from nested leaf
records.** The port raised this after reproducing `[160, 236]` from its own
export, and it is worth stating because the implementation reads correctly either
way while only one is right. Including `GP_TITLE` build 4's `ptloop` leaves, whose
cycles run to 600 and 720, gives **`[269, 540]`** instead — a "settled instant"
that lies *past the end of every top-level element's timeline*, i.e. after the
screen has exited. Verified here: top-level `[160, 236]` width 76, with leaves
`[269, 540]` width 271. A leaf loops on its own clock and says nothing about when
the screen stops changing.

✅ **Confirmed against the running game.** The mechanism this page decodes — five
transient flashes that fire and vanish — is observed in the guest's own draw
stream, with `ptlogo_back2eff1` drawn in exactly two frames at t = 54.0 against a
decoded peak of t54–56: [`ui-title-buildin-measured.md`](ui-title-buildin-measured.md).

## The case that found it

`GP_TITLE` build 4. Seven elements share the light-arc band behind the logo:

| element | timeline | at rest | at t=198 |
|---|---|---|---|
| `ptlogo_back2eff1.t32` | a=0 → **255 at t54–56** → 0 by t58 | **255** | 0 |
| `ptlogo_back2eff2.t32` | a=0 → **255 at t58–60** → 0 by t62 | **255** | 0 |
| `ptlogo_back2eff3.t32` | staggered, same shape | **255** | 0 |
| `ptlogo_back2eff4.t32` | staggered, same shape | **255** | 0 |
| `ptlogo_back2eff5.t32` | 255 at t64–66 → 192 at t74 → **0 by t110** | **255** | 0 |
| `ptlogo_back2eff.t32` | 255 at t66, **holds to t238**, exits t244 | 255 | 255 |
| `ptlogo_back2.t32` | 255 at t80, **holds to t243**, exits t249 | 255 | 255 |

The five numbered ones are a single light sweep travelling left to right across
the logo, drawn as five staggered two-frame flashes. They are all extinguished by
t110. `rest()` draws them **simultaneously and permanently**, and five stacked
white glows (`ptlogo_back2eff5.t32` decodes to a mean opaque RGB of exactly
255,255,255) drive the arc to saturation.

## What it looks like

![the light arc: console, rest(), and --settle](../captures/title-builds/title-arc-rest-vs-settle.png)

The console's arc is a **thin white outline with a pink hooked tail**. `rest()`
renders a fat solid white blob that swallows the tail completely — five white
glows stacked. `--settle` reproduces the console.

⚠️ A measurement trap worth recording: sampling the *brightest 3 %* of that band
gives (252,245,239) for the console against (255,255,255) for `rest()` — nearly
neutral, and it reads as "no hue difference". That statistic samples the white
outline in both and never touches the pink tail. What it *did* expose was the
count: at a 97th-percentile threshold the console has 1 459 pixels above it and
`rest()` has 8 581, i.e. a saturated plateau. **The pixel count carried the
signal that the mean colour hid.**

## The measurement

Against
[`live-title-build4-no-plate.png`](../captures/title-builds/live-title-build4-no-plate.png),
whole frame and over the arc band (y 95–215, x 830–1230). The third column counts
pixels at or above the band's 97th-percentile luminance — a *saturation* statistic,
independent of the error being minimised, and not fitted.

| | mean abs diff | arc band | clipped px |
|---|---|---|---|
| **console capture** | — | — | **1 459** |
| `rest()` — the default | 14.07 | 33.22 | 8 581 |
| **`--at 198` — predicted from the disc** | **12.06** | **11.79** | **1 452** |
| `--at 100` — control, before the window | 19.13 | 20.46 | 1 468 |
| `--at 358` — control, past every exit | 28.80 | 53.37 | 1 447 |

**t=198 was computed before the render was scored.** `settle_window()` on build 4
returns `[160, 236]`; 198 is its midpoint. A separate sweep of t in 40…300 finds a
flat optimum over t ∈ [180, 238] at 12.06 / 11.79 / 1 452, which contains the
prediction.

⚠️ The clipped-pixel count discriminates `rest()` from *any* single instant — the
two controls also land near 1 459 — so it identifies the **blow-out**, not the
time. The time is identified by the mean, and by the disc.

## The controls

* ✅ **`at = None` is byte-identical.** `compose` with no `at` produces the same
  bytes before and after this change (`cmp`, exact). The default path is untouched.
* ✅ **The change did not regress the resting composite.** Rendering build 4 at
  `formats-pin-2026-08-29c` (pre-rotation, pre-leaf) and at the current tree both
  give **14.07 / 33.22**.
* ✅ **A hand-picked visibility list reaches the same answer.** Leave-one-out over
  all 24 elements, then hiding exactly `eff1`…`eff5` and keeping the two holders,
  gives 12.06 / 11.79 / 1 452 — identical to `--at 198`. The principled rule
  reproduces the hand-picked one with nothing hand-picked.
* ✅ **Disc-wide self-consistency.** For every bundle with a window, no element has
  a keyframe strictly inside it, and the midpoint lies within it —
  `tests/ui_settle_time_disc.rs`.

## 🔴 Reach: this does not apply to every bundle

Of the **1 758** composable bundles carrying two or more keyframe times:

| | count | share |
|---|---|---|
| settle window ≥ 30 units (0.5 s) | 524 | 30 % |
| settle window < 10 units | 731 | 42 % |
| mean window | 49 units | — |

The 42 % are mostly `loop*` animation fragments, which are **meant** to be in
motion and have no settled pose to find. **Check the window width before trusting
the midpoint.** A narrow window is the data saying "this bundle never settles",
not a settle time with a small error bar.

## What this corrects elsewhere in the corpus

* 🔴 [`ui-rotation-implemented.md`](ui-rotation-implemented.md) records the pose
  scan as **"Flat. No minimum."** over t = 0…600. The cause is now known:
  `ComposeOptions::at` was posing **leaves only**, so the scan moved the light
  sweeps and never touched the top-level flashes. No `t` could have helped. `at`
  now poses every element.
* 🔴 The same document blames the residual on our renderer **"not drawing
  `ptlogo1` / `ptlogo2` at all (four elements)"**. That is **withdrawn**. Build 4
  declares *six* ptlogo elements: indices 0 and 1 are kind `0x0` at (184,193) and
  (137,308), alpha 255, and are **drawn**; indices 2–5 are kind `0x4` ghost
  instances at (−116,−7) and (437,508), alpha 0, and are skipped deliberately.
  Hiding element 0 makes the error **worse** by +5.20 whole-frame and +7.61 in the
  band; element 1 by +7.47. They are drawn and correctly placed.
* ❔ The **10.92** baseline in that document's table is **not reproducible**.
  `screen render --build 4 --black` against that capture gives 14.07 at the
  pre-change tag and 14.07 now. Some element of that recipe was not recorded.
  Conclusions resting on 10.92 — including the "1.7 % better" verdict on rotation
  — should be treated as unverified until the recipe is recovered.

## What is not settled

❔ The remaining **12.06**. It is broad and level-like rather than localised,
which is consistent with the tone term that
[`title-residual-tone-vs-geometry.md`](title-residual-tone-vs-geometry.md)
measures. The arc band is no longer where the error lives.

## Reproducing

```bash
cargo run -q -p sylpheed-cli -- screen render --build 4 --black --at 198 \
  "$SYLPHEED_DISC/dat/GP_TITLE.pak" /tmp/title.png
SYLPHEED_DISC=/disc cargo test -p sylpheed-formats --test ui_settle_time_disc
```