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`](data/splash-quad-timeline.txt) and
[`data/splash-draw-pass-census.txt`](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.**

---

## 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`](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`](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`](ui-keyframe-time-unit.md)), and the plate-late
finding (play-test 3), which is untouched.