Sylpheed/docs/re/structures/ui-leaf-vs-parent-alpha.md

✅ A nested .rat leaf animates on its OWN timeline — the parent's alpha does not multiply in

Status: ✅ DECODED, against a GPU draw capture rather than our renderer. Answers the port's question: it emits both a parent record and its nested leaf, each with its own alpha ramp over a different span, and would not draw the leaf without knowing the composition rule.

The question

For the title's light sweeps, parent and leaf disagree about everything:

	ptloop01 parent	its leaf pteff03.t32
alpha	0 → 255 over t=70…100, held to 238, → 0 at 250	255 → 128 at t=150 → 255 at 540
scale	(100, 100)	(100, 600)
rotation	0	+30°
x	fixed 441	−639 → −39 → 1521

ptloop02's leaf pteff03a.t32 is the mirror: (100, 800), −45°, x sweeping 1721 → 1111 → −839, alpha 0 → 128 → 255.

The oracle

The per-draw capture records vertex colours, and on the title's ptloop draw (draw 2) they are C3FFFFFF and B6FFFFFF — alpha 195 and 182, not 255. So the composed alpha the game actually submitted is observable.

The measurement

Fitting only the two alphas to the two leaf ramps gives a single consistent time, t = 355:

	leaf value at t=355	observed
quad A alpha	194.8	195
quad B alpha	182.2	182
parent alpha (both)	0	—

🔴 Multiplying the ramps is refuted. The parent has expired by t=355 (it returns to 0 at t=250 and a group holds at its last keyframe), so leaf × parent / 255 predicts 0 for both quads — the sweeps would be invisible. They are drawn, at 195 and 182.

✅ And the position check was PREDICTED, not fitted. Nothing about x entered the fit; the same t=355 then places the quads from the leaves' own sweeps:

	from the leaf at t=355	measured off the capture
quad A centre x	981	992.0
quad B centre x	478	467.2

Within ~11 px, on 400-px-wide quads travelling 1 560 and 1 950 px. Four quantities — two alphas and two positions, from two differently-shaped ramps — all agree on one time.

The rule

A leaf carrying geometry animates on its own timeline. The parent's alpha does not gate it. For these records the parent is a container: it has no sprite, and its keyframes describe nothing that is drawn.

⚠️ Reach, and it is not a universal rule about leaves. This is one draw, one capture, one element pair, and it is specifically the case where the parent carries no geometry. The opposite case is already recorded: for a button, a base record's leaf duplicates the parent and the parent wins (ui-button-focus-record.md). So the discriminator is which record actually carries the geometry, not a fixed precedence.

❔ What is not established: whether the parent alpha would multiply in during a window where it is non-zero. Every observation here has parent = 0, so "the leaf wins" and "the parent is ignored because it has nothing to draw" are not separated. A capture during t=100…238 would separate them.

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🔴 The port's x = −324 is the OLD keyframe association, applied to leaves

Implementing the rule above, the port reported the leaf's top-left at x ≈ −324 at t=355 — off-screen left — against 781 (centre 980.5) here. Both cannot be right, and the disagreement is not about rotation or pivots.

Their stated pairing is "t=150 at x=−639, t=540 at x=−39". On the disc the leaf reads:

pose x	its time	the time it would take under the OLD association
−639	0	150
−39	150	540
1521	540	600
1521	600	—

Their pairing is the second column. Each pose is taking the next pose's time — which is exactly the association ui-keyframe-record-layout.md refuted and HANDOFF carries a red banner about: a keyframe's time comes before its pose. Feeding their pairing into the same interpolation reproduces −324 to the digit.

✅ With the corrected association, t=355 gives top-left 781, and centre 980.5 for a 399-wide sprite — against 992.0 measured off the capture.

⚠️ So this is the same defect as the top-level one, in the leaf path. The top-level parser was corrected on 2026-08-29; a leaf is read by parse_build on a sub-slice, so anything reading leaves through a separate path can still carry the old association. That the alphas nonetheless matched is the trap: alpha at t=355 is inside a long segment where a one-keyframe shift barely moves it, while x is sweeping 1 560 px over the same span and the shift is glaring. A rule can look confirmed on the insensitive quantity and be wrong on the sensitive one.

✅ The 11.5 px residual is CLOSED — it was the alpha-only fit's resolution

Left open above as "do not fit to close it". It is closed by adding observables, not by tuning a parameter.

The draw's vertex buffer carries positions and colours at the same instant, so all four quantities must agree on one t. Solving for t from each independently:

observable	solved t	sensitivity	its own precision
quad A x	357.88	4.00 px/unit	±0.12 units
quad B x	357.58	4.06 px/unit	±0.12 units
quad A alpha	355.75	0.326 levels/unit	±1.54 units
quad B alpha	354.09	0.265 levels/unit	±1.89 units

⚠️ The alphas are ~50× less precise per unit of time, because alpha is a byte changing by only ~0.3 levels per keyframe unit — so a single level of quantisation is worth 1.5–1.9 units, which at 4 px/unit is 6–8 px of sweep. The 11.5 px was that, not geometry.

At the position-derived t = 357.7, every observable lands:

	predicted	measured	diff
quad A centre x	991.30	992.0	−0.70 px
quad B centre x	466.72	467.2	−0.48 px
quad A alpha	195.64	195	+0.64
quad B alpha	182.95	182	+0.95

✅ Sub-pixel on both positions, inside one byte on both alphas — while the parent's alpha is 0 throughout. And the leaf pivot is (200, 90) against a 399×180 sprite, so rotation displaces the centre by essentially nothing and there is no pivot/rotation correction to find.

⚠️ To half a pixel, not exactly (the port's check, and worth keeping): the sprite is odd-width, so its true centre is 199.5, and the declared pivot is 200. The 0.5 px offset is far inside the −0.70 / −0.48 px agreement above and changes nothing here — but do not lean on "the pivot IS the centre" for a sub-pixel claim. It is the centre rounded up.

⚠️ The methodological point is the same one this exchange started with, inverted. Earlier, a rule looked confirmed because it was checked against alpha — the insensitive field. Here the same insensitivity produced a spurious 11.5 px residual. The insensitive quantity does not just fail to falsify; it manufactures apparent error. Solve on the fastest-moving field and check the slow one, never the reverse.

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🔴 Refutation — "125 % is the only non-whole-multiple scale" is WRONG, and by a lot

DECISIONS.md records title_jp's ptlogo_eff2 at 125 % as "the single drawn element in the whole export at a scale that is not a whole multiple of 100 %". That census was over parents only. Opening the 45 leaves as well (--example scale_census, output at data/ui-scale-census-with-leaves.txt):

scale	count	where
75,75 · 96,96 · 99,99	4 each	pgloading_loop4.rat on all four loading screens
75,100 · 96,100 · 99,100	4 each	pgloading_line.t32
101,101 · 103,103 · 112,112	12 each	ptlogo1 / ptlogo2, entries 4 and 7
150,150	28	pgloading_loop1.rat
204,208 · 210,220	1 each	ptlogo_eff2 … no: ptlogoall_eff.t32, entry 4
250,250	2	pgloading_loop5.rat → LEAF pgloading_ring.t32
125,125	2	ptlogo_eff2.rat, entry 7

Thirteen distinct non-whole-multiple scales, and 125 % is among the rarest at 2 occurrences. ptlogo1/ptlogo2 carry 101/103/112 on the English title too, so this is not a Japanese-build peculiarity. ⚠️ The claim's real content was "the only one the port draws", which is a statement about the export's element set, not about the disc.

✅ And ptlogo_eff2 itself is decoded — the 125 % is a POP, not a steady scale

PARENT ptlogo_eff2.rat   pivot (169,169)
  t=0    a=0    scale (100,100)   pos (412,96)
  t=50   a=0    scale (0,0)
  t=59   a=255  scale (125,125)
  t=71   a=255  scale (125,125)
  t=107  a=0    scale (0,0)
LEAF  ptlogo_eff2.t32  kind 0x8   a=160  scale (100,100)  rot 0 → 360 over t=0…960
LEAF  ptlogo_eff2.t32  kind 0xc   a=80   scale (100,100)  rot 0 → 360 over t=0…960

• The 125 % lasts 57 units (~0.95 s) — a scale-0 → 125 % → scale-0 flash between t=50 and t=107. It is a transient, not a steady state, which is why it looks anomalous in a census of resting poses.
• The leaf draws at 100 %, as two superimposed copies of the same sprite at alpha 160 and 80, each rotating a full 360° over 960 units — a slow double-layered spin, 16 s per revolution at 60 units/s.

🔴 And this is exactly the case my ptloop rule could NOT separate. There the parent had expired (alpha 0, no sprite) so "leaf wins" and "parent ignored" were indistinguishable. Here the parent carries real geometry — a scale that reaches 0 twice. If parent scale gates the leaf, the spin is a 0.95 s flash; if the leaf runs on its own timeline, it spins continuously for 16 s. The two readings differ enormously and nothing on the disc chooses between them.

❔ Undecodable here, with reach: title_jp has no oracle capture, so this cannot be adjudicated in this container at all. The port is right to withhold it. A capture of the Japanese title would settle it — and that is the same Japanese-locale capture MISSION has parked as 🟡 since 2026-08-29.