Sylpheed/docs/port/splash-animation-fixed.md

The splash: frozen, then fixed, and now checked for SHAPE as well as motion

Status: ✅ animates, and the ramp matches the declared curve. Written 2026-09-02 by the Port; HANDOFF on this branch answers 9ca1eb5.

The 2026-09-02 play-test found the splash frozen. The cause and the fix are in the commit history; this page is the part that comes after — is the animation now the right animation? motion-census says explicitly that it cannot answer that: "a wrong ramp that moves every frame passes here."

Pre-registered (R2)

palogo_sqex_eff declares 0:a=0 → 15:a=255 → 30:a=212 → 45:a=0 — three segments, three gradients:

segment	declared
0 → 15	+17.0 per unit
15 → 30	−2.87 per unit
30 → 45	−14.13 per unit

So a film should show three straight runs with breakpoints at 15 and 30, the middle slope about 1/5 the magnitude of the last, and the rise about 1.2× the last.

Measured, from a film of a real boot

Region: 686x11+299+319 — the companion's top strip, which no other element overlaps, so the number is that element's own alpha and not a composite.

view units	strip mean	slope/unit
5.58	0.02809
10.00	0.05086	+0.00515
13.04	0.06611	+0.00503
16.12	0.07530	+0.00298 ← crossing the breakpoint
19.21	0.07260	−0.00087
25.38	0.06695	−0.00092
28.39	0.06482	−0.00071
31.39	0.05719	−0.00254 ← crossing the breakpoint
34.39	0.04471	−0.00416
40.39	0.01910	−0.00428
43.39	0.00655	−0.00418
46.39	0.00000	gone

Breakpoints land where declared: the rise stops between 13.0 and 16.1, the gentle fall steepens between 28.4 and 31.4.

ratio	declared	measured
middle : last	0.203	0.213
rise : last	1.20	1.20

Within 5 % and exact respectively. The port interpolates piecewise-linearly across the declared segments — which is what the Decoder independently measured the game doing (28 distinct alphas over 28 consecutive presents, modal steps −3 and −14 against predicted −2.87 and −14.13).

⚠️ Ratios, not absolutes, and deliberately. The strip mean is an alpha scaled by whatever the sprite's own pixels are; its absolute value carries the texture. A ratio between segments divides that out, which is why the shape is checkable from a composite at all. Anyone quoting 0.00515 as an alpha is misreading it.

What this still does not establish

• That it looks right. Three instruments have now agreed with a picture a human called wrong, and the fourth agreeing does not change the standing of the fifth. A play-test is the check.
• Anything about the developer splash's three logo/companion pairs. One element, one screen. ✅ Closed below, and the developer splash turned out to be the far better test.
• The absolute alpha. The shape matches; whether the port's alpha equals the game's at a given unit is verify-capture's question, and it answers 0.01 % at the settled pose only.

---

✅ The developer splash: three elements, TWO declared shapes, on one screen

The publisher check above had a structural weakness I named at the time: one element, one screen, one shape. If the port applied some single ramp to everything, that check would pass.

The developer splash cannot be fooled that way, because it declares two different shapes at once:

element	declared alpha	middle segment
palogo_gamearts_eff	0:0 15:255 30:255 45:0	flat
palogo_seta_eff	0:0 15:255 30:255 45:0	flat
palogo_anima_eff	0:0 15:255 30:212 45:0	decays 17 %

Same screen, same frames, same clock, same code path. The two flat elements are the control for the one that is not — no second run, no second renderer, and nothing for a phase or rate error to hide behind, because any such error hits all three identically.

Pre-registered, before the film was read

In units 15→30, gamearts and seta hold flat while anima falls gently. All three fall steeply 30→45.

Measured, off a real filmed boot

Companion-only strips (each companion's rectangle minus the logo sitting inside it), mean luma, --film-interval=0.03:

segment     units 16-29  units 31-44
gamearts       +0.00000     -0.00101
seta           +0.00000     -0.00151
anima          -0.00001     -0.00003

The two flat ones are flat to five decimals. The decaying one decays. And all three fall over 31–44, so the flatness is not a dead element.

The quantitative version, and the falsification arm

Each trace normalised by a single solved gain — one scalar per element, not a per-point fit — against the declared curve, over the whole t=0..45 ramp:

element	fitted against	max err	rms err
gamearts	its own (flat)	0.49 %	0.23 %
seta	its own (flat)	0.50 %	0.27 %
anima	its own (decay)	2.18 %	1.19 %
gamearts	anima's decay	8.32 %	4.80 %
seta	anima's decay	8.08 %	4.86 %
anima	flat	8.82 %	4.94 %

Both directions. Every element fits its own declared shape 4–17× better than it fits the other one available on the same screen. A port that drew one ramp for all three would sit at ~8 % on at least one row; none does.

anima's 2.18 % is the loosest row and the reason is its signal: its companion-only strip means ~0.0005 against gamearts's ~0.015, thirty times dimmer, so its noise floor is thirty times higher in these units. It still separates from the wrong curve by 4×.

What this adds over the publisher check

The publisher check established that the ramp has the declared breakpoints and slope ratios. This establishes that the ramp is per-element — that the port reads each element's own keyframes rather than applying a screen-wide curve. That is a different failure mode, and it is the one that would have survived the publisher check unnoticed.

What it still does not establish

• That it looks right. This is instrument five. The standing of a human's eyes is unchanged by it.
• The absolute alpha, for the same reason as above — a solved gain is deliberately scale-free, so this is a shape result and says nothing about whether the port's alpha equals the game's at a given unit.
• Anything about the logo elements. Both checks measure the pre-blurred companions, because those are the strips that can be isolated from the sharp logo underneath them.