07e93ce041
Answers the question the port agent asked: does the `PRESS A` plate's pulse group loop from its start, or hold at alpha 0 between cycles? It holds. A nested record is itself a RATC bundle with its own header, and that header's `+0x08` is the loop length -- the same field ui_header_time_disc already tests as an animation length at the top level. Its keyframes need not fill it, and the slack is a hold at the final pose. `ptbtn00f` is 105 units of ramp inside a 120-unit cycle, so the glow rests dark for 15 units between pulses. The five main-menu focus records fill their 120 exactly, which is what shows the slack belongs to this record rather than to the format. Disc-wide over 1 781 timed nested records: 92.3% declare exactly their last keyframe time, 7.7% declare more, and 0 declare less. That last row is the falsifier -- a cycle cannot restart before its own last pose -- and it never fires; the 7.7% is what keeps the reading from being an unfalsifiable relabelling of the keyframes. Falsification against the running game, using a pacing factor measured INDEPENDENTLY on the main menu's focus ring (declared 120 units, measured 2.177 s, factor 1.0885): to reach the corpus's four measurements of the plate pulse (2.12/2.19/2.34/2.31 s), a 105-unit period needs a factor of 1.211-1.337, which EXCLUDES the ring's; a 120-unit period needs 1.060-1.170, which CONTAINS it. Predicted 2.177 s against a measured 2.12-2.34. The two elements are in different bundles and were measured in separate runs; the only thing tying them together is that both declare 120. So the port should stop shipping 105. Its 123-vs-129 ambiguity straddled the right answer without containing it, and 129 only fitted because it was 105 + the exit_ramp_units constant it has since correctly deleted. Reach is stated: this says where a cycle ends, not which records cycle, and the TOP-level +0x08 is a different field left untouched -- every GP_TITLE entry declares 300 while its elements end at 244-269. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01QsEPXWVaEpyfudtR6re1Pd
107 lines
5.0 KiB
Markdown
107 lines
5.0 KiB
Markdown
# A nested record's `+0x08` is its loop length — and the plate holds dark for 15 units
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**Classification: decoded.** The field is read from the disc and checked
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disc-wide (1 781 records, 0 violations). The consequence for the `PRESS Ⓐ` plate
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is then tested against the corpus's existing measurements of the running game,
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which it passes and the previous reading fails.
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## The question
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The port asked it directly: the plate's pulse group runs t=0 → t=105 with alpha 0
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at both ends. **Does it loop from its start, or hold at alpha 0 between cycles?**
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It matters because a 105-unit period is **1.750 s**, and the corpus timed the real
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pulse four times at **2.12 / 2.19 / 2.34 / 2.31 s** — about 17 % longer. The port
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shipped 105 anyway, saying the disc's number was wrong, because the alternative
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(129) was built on an `exit_ramp_units` constant that a decode had just deleted.
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## The answer: it holds, and the period is 120
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A nested record is **itself a RATC bundle, with its own header**, and that
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header's `+0x08` is a frame count — the same field
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[`ui-header-time-disc`](../../crates/sylpheed-formats/tests/ui_header_time_disc.rs)
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already tests as an animation length at the top level. Read it on the record and
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the answer is immediate:
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| record | `+0x08` | largest keyframe | slack |
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|---|---|---|---|
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| `ptbtn00f.rat` — the plate glow | **120** | 105 | **15** |
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| `ptbtn01f` … `ptbtn05f` — main menu focus | 120 | 120 | 0 |
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| `ptloop01.rat` | 600 | 600 | 0 |
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| `ptloop02.rat` | 720 | 720 | 0 |
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**The glow ramps 0 → 80 → 0 over 105 units inside a 120-unit cycle, so it rests
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dark for 15 units between pulses.** The five main-menu focus records fill their
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cycle exactly, which is what shows the slack is a property of *this record* rather
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than of the format.
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## Disc-wide
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[`record-loop-length-census.txt`](../data/record-loop-length-census.txt) — every
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nested record on the disc that has a timed keyframe:
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| | count | share |
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|---|---|---|
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| nested records with timed keyframes | 1 781 | — |
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| `+0x08 == ` largest keyframe time | 1 643 | 92.3 % |
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| `+0x08 > ` largest keyframe time (a hold) | 138 | 7.7 % |
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| **`+0x08 < ` largest keyframe time** | **0** | **0.00 %** |
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The last row is the falsifier and it never fires: **no record declares a cycle
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that would restart before its own last pose.** The 7.7 % is what keeps the reading
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from being an unfalsifiable relabelling of the keyframes — if every record
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declared exactly its own last keyframe time, the field would carry nothing.
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## The falsification test against the running game
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Both hypotheses are periods in declared units, and both have to be converted by
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the same emulator pacing factor. That factor is measured **independently**, on the
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main menu's focus ring: declared 120 units, measured **2.177 s**
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([`focus-ring-spin-measured.md`](../focus-ring-spin-measured.md)), so the factor
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is **1.0885** against a nominal 60 units/s.
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| plate period | nominal | factor it would need to reach 2.12–2.34 s | verdict |
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|---|---|---|---|
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| 105 units | 1.750 s | **1.211 … 1.337** | 🔴 **excludes** the ring's 1.0885 |
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| **120 units** | 2.000 s | **1.060 … 1.170** | ✅ **contains** the ring's 1.0885 |
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At 120 units and the ring's own factor the plate should pulse every **2.177 s**,
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against a measured 2.12–2.34 s. **105 cannot reach the measured range under any
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pacing factor that the ring also satisfies.**
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This is a genuine test rather than a fit: the ring and the plate are different
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elements in different bundles, measured in separate runs, and the only thing tying
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them together is that both declare a 120-unit cycle.
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## What this replaces
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* 🔴 **105 is wrong** and the port should stop shipping it. The number is **120**,
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and it comes from the disc — not from `exit_ramp_units`, the deleted constant
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whose 129 happened to fit.
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* ✅ **The port's ambiguity is genuinely resolved**, just not the way it read: the
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old 123-vs-129 pair straddled the right answer without containing it.
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* ⚠️ **The 2.24 s mean is still ~3 % above the 2.177 s prediction.** That is inside
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the spread of the four measurements (2.12–2.34) and is not evidence of a further
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hold; it is what a four-sample wall-clock measurement of a ~2 s period in this
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emulator looks like.
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## Reach
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⚠️ **This says where a cycle ends, not that every record cycles.** 92.3 % of
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records declare no slack at all, and a record whose element is not in a repeating
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state (a button's base record, a one-shot build-in) has a length that is simply
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its own duration. Nothing here establishes *which* records the game restarts —
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only that when one does, `+0x08` is where.
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❔ **The top-level `+0x08` is not the same thing.** Every `GP_TITLE` entry declares
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300 there while its elements end at 244–269, and no screen visibly repeats every
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5 s. Whether the top-level field is a loop length, a budget or something else is
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untouched by this.
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## Reproducing
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```bash
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cargo run -p sylpheed-formats --example record_loop_length
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SYLPHEED_DISC=/disc cargo test -p sylpheed-formats --test ui_record_loop_length_disc
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```
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