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port: F6 unit a -- where the sweep IS when the plate arrives, and a window that settles two questions

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Answers the Decoder's direct question: the port positions the leaf from the
LEAF's own clock, it does not draw the parent's pose and ignore the translation.

Computed from the leaf translation: pteff03 enters the frame at t=61 and is
mid-screen (x=305) when the plate reaches full alpha at t=236 -- visible and
travelling for ~175 units before the plate.

And screen_view.gd's own flagged limit -- 'a capture during t=100..238 would
separate' leaf-wins from parent-ignored-because-it-draws-nothing -- is the SAME
interval F6 is about. Applying the parent would hide the sweep until t=70 and
dim it to t=100, which accounts for ~40 units of the earliness but not the other
~175. One capture in that window settles both questions.
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Sylpheed port agent
2026-09-02 18:20:38 +00:00
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docs/port/f6-what-starts-the-sweep.md
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@@ -57,6 +57,40 @@ with `pteff03` having already crossed the measured band and with the coarse
resize washing a thin glow out. **The film neither adds to nor contradicts the
declaration; the declaration is the evidence here.**
## Where the sweep actually is, computed from the leaf's own translation
The port positions the leaf **from the leaf's own clock** — it does not draw the
parent's pose and ignore the translation. Sprite 399 wide on a 1280 screen:
| t | 0 | **61** | 70 | 100 | 150 | **236** | 250 |
|---|---|---|---|---|---|---|---|
| `pteff03` x | −639 | **−395** | −359 | −239 | −39 | **305** | 361 |
| `pteff03a` x | 1721 | 1477 | 1436 | 1314 | 1111 | 762 | 705 |
**`pteff03` enters the frame at t=61 and is mid-screen at t=305 when the plate
reaches full alpha at t=236** — visible and travelling for ~175 units ≈ 2.9 s
before the plate. `pteff03a` enters much later.
## 🔴 The open question in this file sits exactly inside F6's window
`screen_view.gd` flags its own limit on the leaf-vs-parent alpha decode:
> *"Every observation behind this has parent alpha 0, so 'the leaf wins' and 'the
> parent is ignored because it draws nothing' are NOT separated. **A capture
> during t=100…238 would separate them.**"*
The parent is non-zero exactly on `t=100…238`, and the plate arrives at 236. So
that unresolved ambiguity is **the same interval F6 is about**, and it is
load-bearing for the first stretch: the parent ramps 70→100, so applying it would
hide the sweep until t=70 and dim it to t=100, while the port shows it at full
alpha from t=61.
That accounts for ~40 units of the earliness. **It does not account for the other
~175**, which is the leaf clock starting at title t=0 with no offset.
📌 **One capture in `t=100…238` would settle both** — F6's start time and the
leaf/parent alpha rule — rather than two.
## What changes when the answer lands
A start time is an **offset**, and `leaf_time_units` is an absolute override —