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re(ui): the keyframe-time shift is favoured 26x by timing, rejected by a render

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Follow-up on last iteration's unadopted candidate (+36 holds the NEXT
pose's time, not its own). Two new results, pointing opposite ways, and
both are reported.

FOR, and calibration-free: the observed full-alpha hold : fade-out ratio
on palogo_gamearts is 83 : 13 frames = 6.38. The shifted reading predicts
8.00. The current reading predicts 0.25 -- off by 26x. With the glow's 2
units/frame fixed and nothing else free, the current reading says the
logo holds full alpha for 2.0 frames; the capture holds it for 83. This
is no longer the shape argument the candidate rested on.

Also for: rest()'s plain max-dwell fallback picks a=0 -- a transparent
pose, for a publisher logo -- under the current reading, and the visible
a=255 hold under the shift. Only the rest_plateau special case rescues
the render today, and that is the case the port agent reported a bug in.

AGAINST: rendering every build of six UI paks under both readings, 10 of
11 compared are byte-identical and one changes -- GP_TITLE build 7, the
Japanese twin of build 4, by 13.1% of pixels. Build 4, the one verified
against a live capture, is unchanged either way, so the single build the
shift moves is the one with no capture to adjudicate it. The proxy goes
against the shift: language twins are the same artwork, and build 7 reads
70.94 mean luminance as decoded against build 4's 71.41, but 76.32
shifted. Correlation does not separate them (0.6206 vs 0.6201).

These constrain different things -- timing versus pose selection -- and
rest() is a heuristic layered on the times, so moving the times moves its
tie-breaks. Adopting the shift means revisiting that heuristic in the
same change, with no build-7 capture to verify against.

Default UNCHANGED. Experiment reachable via SYLPHEED_KF_TIME_SHIFT=1.
Shifted-mode suite: 122 passed, 0 failed across 3 suites at commit time.
This commit is contained in:
Sylpheed RE agent
2026-08-28 23:03:55 +00:00
parent 531840b417
commit 6f23f4d113
5 changed files with 139 additions and 7 deletions
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13
crates/sylpheed-formats/src/ui_layout.rs
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@@ -450,6 +450,8 @@ fn mark_focused_states(elements: &mut [Element]) {
/// Read the placement region that follows the declaration table, filling in each
/// element's keyframe group.
fn parse_placements(bundle: &[u8], elements: &mut [Element]) -> Vec<usize> {
// Experiment gate, default off; see the `time` field below.
let shift_times = std::env::var("SYLPHEED_KF_TIME_SHIFT").as_deref() == Ok("1");
let count = elements.len();
let mut order = Vec::with_capacity(count);
let mut pos = DECL_TABLE_AT + count * DECL_ENTRY;
@@ -485,7 +487,16 @@ fn parse_placements(bundle: &[u8], elements: &mut [Element]) -> Vec<usize> {
x: be32(bundle, blk + 28) as i32,
y: be32(bundle, blk + 32) as i32,
// Only a block wholly inside the group carries a time.
time: (blk + 40 <= group_end).then(|| be32(bundle, blk + 36)),
//
// ⚠️ Which block a time word BELONGS TO is under test — see
// `docs/re/ui-keyframe-time-unit.md`. Set `SYLPHEED_KF_TIME_SHIFT=1`
// to read `W[k-1]` as block `k`'s time ("the word is the time the
// NEXT pose is reached") instead of `W[k]`. Default is unchanged.
time: if shift_times {
(k >= 1).then(|| be32(bundle, blk - KEYFRAME + 36))
} else {
(blk + 40 <= group_end).then(|| be32(bundle, blk + 36))
},
});
}
elements[idx].keyframes = group;