Sylpheed/docs/re/splash-glow-is-a-baked-texture.md

The splash "blur" is a baked glow texture — palogo_*_eff.t32, a 10-pixel concentric outset

Status: ✅ decoded (disc), confirmed against the oracle 8/8. 2026-09-01. Instruments: prediction ⟨disc⟩ (parse_build + t8ad::parse over GP_TITLE.pak); target ⟨capture⟩ (the guest vertex stream in data/splash-quad-timeline.txt and data/splash-draw-pass-census.txt).

Answers play-test finding 4 — "the splash fade/blur is more pronounced in the game" — at the level the human asked for: the mechanism, not a curve.

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The answer in one line

There is no blur pass and no blur filter. Each logo ships a second texture that IS the blur — palogo_<x>_eff.t32, the same artwork outset by exactly 10 pixels on every side — and the game draws it as an extra alpha-over quad concentric with the logo. Drawing the logo alone loses the glow entirely.

ui-splash-draw-pass.md had already excluded a post-process from GPU state and closed with "that softness is in the texture or in which quads are drawn, not in a pass", leaving the two unseparated. It is both, and they are the same fact: a dedicated soft-edged texture, drawn as its own quad.

1 — the capture's eight anonymous quads, named from the disc

A draw capture sees geometry, not names. splash-quad-timeline.txt could only call them Q0…Q7. Predicting each rect from the declared position and the decoded sprite size — x_ndc = 2x/1280 − 1, y_ndc = 1 − 2y/720 — names all eight, bijectively:

sprite (disc)	quad	max abs edge error	runner-up	draws
palogo_sqex.t32	Q0	0.0056	0.0367	111
palogo_sqex_eff.t32	Q7	0.0061	0.0339	8
palogo_gamearts.t32	Q1	0.0056	0.0272	87
palogo_gamearts_eff.t32	Q4	0.0037	0.0306	21
palogo_seta.t32	Q2	0.0050	0.0278	87
palogo_seta_eff.t32	Q5	0.0037	0.0328	21
palogo_anima.t32	Q3	0.0050	0.0272	87
palogo_anima_eff.t32	Q6	0.0056	0.0356	21

8 named, 0 unmatched. The capture quantises to 0.01 NDC, so the tolerance is 0.010; every match lands at ≤ 0.0061 and every runner-up sits at ≥ 0.0272 — a 4.5× to 8.9× margin. That margin is the control: eight similar boxes would match anything, and these do not.

Reproduce: cargo run --release -p sylpheed-formats --example splash_quad_names.

📌 This also settles a ⟨our-reader⟩ 🟡 in the right direction. The prediction comes from our reader; the target is the oracle's vertex buffer. The agreement is therefore evidence about the reader, not a claim resting on it — parse_build's declared placement and t8ad's decoded dimensions reproduce what the GPU actually drew, on both splash bundles, to within 4 screen pixels. A disagreement would have indicted the reader instead.

2 — what an _eff companion actually is

splash-quad-timeline.txt described the companions as "the same three rects scaled slightly larger". That is an inference from four rounded NDC numbers, and the disc refutes it:

palogo_sqex_eff       outset 10x10 px, centre off by ( 0.0,-0.5), scale 1.030/1.309  NOT uniform
palogo_gamearts_eff   outset 10x10 px, centre off by (-0.5, 0.0), scale 1.042/1.282  NOT uniform
palogo_seta_eff       outset 10x10 px, centre off by ( 0.5,-0.5), scale 1.087/1.236  NOT uniform
palogo_anima_eff      outset 10x10 px, centre off by (-1.5, 1.0), scale 1.049/1.147  NOT uniform

	logo	_eff	Δ
sqex	666×68 @ (309,330)	686×89 @ (299,319)	+20×+21 px, −10,−11
gamearts	500×71 @ (390,164)	521×91 @ (379,154)	+21×+20 px, −11,−10
seta	240×89 @ (521,316)	261×110 @ (511,305)	+21×+21 px, −10,−11
anima	388×136 @ (446,449)	407×156 @ (435,440)	+19×+20 px, −11,−9

• Concentric — the two centres agree to ≤ 1.5 px in every pair.
• A constant 10-px outset per side, in both axes, on all four pairs.
• Not a scale. The x and y scale factors differ by 0.06 to 0.28. A "slightly larger copy" model predicts they match; they do not, and the narrower the logo's height the further apart they get — exactly what a fixed-width border does and a scale cannot.

A fixed 10-pixel halo around the same artwork, in a separate texture, is a pre-rendered blur. Nothing computes it at runtime; it was computed by the artist and shipped.

Asserted by eff_is_a_concentric_outset_not_a_scale in the same example, which fails if the pair is not concentric, if the outset is not uniform, if it leaves 8…12 px, or if the scale factors turn out uniform after all — that last assertion is the one that would reinstate the reading it displaces.

3 — the blend, tested out of sample on these exact screens

structures/ui-blend-mode-decoded.md established T8aD +0x04 bit 0x02 on 35 elements over three screens (GP_TITLE entries 2, 4, 5, 6). Entries 10 and 11 were not in that sample, and they are the screens the play-test says are wrong.

Pre-registered before reading the disc: the census finds 0x01010101 (additive) in 0 of 1 048 splash draws, so if the bit generalises, all eight splash sprites must read additive = false.

palogo_sqex.t32 / _eff, palogo_{gamearts,seta,anima}.t32 / _eff
    word04 = 0x00008830  ->  alpha-over        (8 of 8)
additive=0  alpha-over=8  no-header=0
control -- entry 6 through the SAME code path reports additive=9: PASS

Prediction held. The control matters: the same accessor reports 9 additive sprites on entry 6, so additive=0 is a fact about the splashes and not a harness stuck on one answer.

cargo run --release -p sylpheed-formats --example splash_blend_check.

🔴 So the glow is NOT additive. It is composited source-over like everything else, and its softness comes entirely from the texture's own alpha. A port that "adds a glow" by switching these quads to additive blending will be wrong in a new way.

What this means for the port

1. Draw palogo_sqex_eff.t32, palogo_gamearts_eff.t32, palogo_seta_eff.t32 and palogo_anima_eff.t32 as their own quads, at their own declared positions, with their own keyframe alphas. They are not decorations of the logo element and they are not derivable from it.
2. Do not scale the logo to produce them. They are separate art. A scaled logo has a border that grows with the logo; the real one is 10 px regardless.
3. Source-over, not additive, on all eight.
4. They are short-lived. Declared 0@0 → 255@15 → (255 or 212)@30 → 0@45 against the logo's 0@15 → 255@30 → … → 0@210 (developer) / 0@255 (publisher). The halo flashes during the entry and is gone for the whole hold. That is the "more pronounced" moment and it is ~45 units long.

Refutation attempt, recorded per the adversarial duty

Target: ui-blend-mode-decoded.md's "T8aD +0x04 bit 0x02 set ⇒ additive", tested where it was never fitted — the two splash bundles, on the screens under play-test complaint, against 1 048 captured draws.

Result: it SURVIVED, out of sample, 8/8, with a passing control.

Second target, same iteration: splash-quad-timeline.txt's "the same three rects scaled slightly larger". REFUTED — §2. The companions are concentric 10-px outsets, and their x and y scale factors differ by up to 0.28, which a uniform scale cannot produce. The conclusion the phrase supported (there are six quads and an export must draw all six) is unaffected; the model of what the extra three are was wrong, and the wrong model tells a port to scale a sprite.

Reach

⟨disc⟩ for §2 and §3, so both generalise to every screen that uses the same structures — the _eff naming convention and the blend bit are properties of the shipped data, not of a boot. §1's agreement is ⟨disc⟩ × ⟨capture⟩ over the two splash bundles specifically.

Not settled here: whether the _eff alpha ramp the port should use is the declared one or the captured one (they differ; see ui-keyframe-time-unit.md), and the plate-late finding (play-test 3), which is untouched.