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Reuse spanning-aware prepared plan at activate (kill pre-playback pause)

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A spanning block stalled ~2.1s before it began playing: activate ran prepareRevealBlock
with forceRebuild, synchronously redrawing the start spread (and preloading the
continuation spread) on the main thread, because the lookahead plan had been built with
right-only timing before pagination committed the overflow.

Build the start-spread plan spanning-aware during lookahead instead: when the preview
layout shows the block overflows, derive its timing across both preview spreads (via the
revealSpreadSourceOverride) and cache it. activate then reuses that plan — the same fast
cached-plan path non-spanning blocks already use — with no synchronous redraw. forceRebuild
is kept only as a fallback when a block spans but was not prepared spanning-aware (e.g. an
immediate prepare with no preview layout), and an evicted plan still rebuilds correctly
because pagination is committed by then.

Verified live: the spanning block's pre-playback gap dropped from ~2088ms to 139ms (equal
to non-spanning blocks), while the right line still reveals over its area share (~3.3s),
the continuation still animates from the start, and there are no fast-forwards or problems.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
This commit is contained in:
Georg Tomitsch
2026-06-19 00:10:25 +02:00
parent 47af10d60c
commit 28d5e51c92
3 changed files with 61 additions and 34 deletions
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public/js/book-playback-timeline-module.js
+39 -26
View File
@@ -206,30 +206,39 @@ class BookPlaybackTimelineModule extends BaseModule {
});
if (!previewSpread) return null;
const revealDetail = this.createRevealDetail(sentence, previewSpread, 'prepare');
const texturePlan = this.textureRenderer.prepareRevealBlock(revealDetail, {
phase: 'prepare',
publishEvent: false
});
// If this block overflows onto the next spread, prepare that continuation spread's
// reveal plan now (lookahead/background) so revealContinuationSpread reuses it after the
// flip instead of redrawing synchronously. Only during background prepares and when the
// preview layout is available; otherwise the continuation falls back to the redraw path.
if (options.immediate !== true && Array.isArray(previewSpread.previewSpreads)) {
const startIndex = Math.max(0, Number(previewSpread.index || 0));
const continuationSpread = previewSpread.previewSpreads
// Detect a spanning block from the (not-yet-committed) preview layout so its reveal
// plan can be prepared spanning-aware in the background, off the critical path. Only
// during background prepares and when the preview layout is available; otherwise we
// fall back to the synchronous activate rebuild + continuation redraw (today's path).
const previewSpreads = options.immediate !== true && Array.isArray(previewSpread.previewSpreads)
? previewSpread.previewSpreads
: null;
const startIndex = Math.max(0, Number(previewSpread.index || 0));
const continuationSpread = previewSpreads
? (previewSpreads
.filter(spread => spread
&& Number(spread.index) > startIndex
&& this.getBlockRevealSides(spread, sentence.blockId).length > 0)
.sort((a, b) => Number(a.index) - Number(b.index))[0] || null;
if (continuationSpread) {
this.textureRenderer.prepareContinuationRevealPlan?.({
...revealDetail,
previewSpreads: previewSpread.previewSpreads,
continuationSpread
});
}
.sort((a, b) => Number(a.index) - Number(b.index))[0] || null)
: null;
const spanningPlanPrepared = Boolean(continuationSpread);
const revealDetail = this.createRevealDetail(sentence, previewSpread, 'prepare');
// For a spanning block, derive the start spread's timing across both preview spreads so
// the cached plan already spans both pages and activate can reuse it (no rebuild).
const texturePlan = this.textureRenderer.prepareRevealBlock(
spanningPlanPrepared ? { ...revealDetail, previewSpreads } : revealDetail,
{ phase: 'prepare', publishEvent: false }
);
// Also prepare the continuation spread's plan so revealContinuationSpread reuses it
// after the flip instead of redrawing synchronously.
if (continuationSpread) {
this.textureRenderer.prepareContinuationRevealPlan?.({
...revealDetail,
previewSpreads,
continuationSpread
});
}
const targetSpreadIndex = Math.max(0, Number(previewSpread.index || 0));
@@ -247,6 +256,9 @@ class BookPlaybackTimelineModule extends BaseModule {
revealSides,
requiresPreFlip: targetSpreadIndex > currentSpreadIndex,
requiresRightFlip: revealSides.includes('right') && this.requiresRightPageFlipAfterReveal(previewSpread),
// True when this block spans and its plan was prepared spanning-aware in the
// background, so activate can reuse it without a synchronous forceRebuild.
spanningPlanPrepared,
// Snapshot the reveal timings now. A reused lookahead segment can be played by
// a sentence instance whose animation timings were lost; without them the
// reveal can't be word-paced and stretches across the whole TTS.
@@ -313,13 +325,14 @@ class BookPlaybackTimelineModule extends BaseModule {
}
const spread = segment.activeSpread || segment.previewSpread;
const revealDetail = this.createRevealDetail(sentence, spread, 'activate');
// For a spanning block the prepared reveal plan was built during lookahead before
// the continuation was committed, so it is right-only. Rebuild from the committed
// spreads so the reveal timing spans both pages (right page no longer absorbs the
// whole duration) and the continuation has reveal regions.
// A spanning block needs timing across both pages. When the plan was prepared
// spanning-aware during lookahead (the common case), reuse it — no synchronous redraw
// on the critical path. Only when it spans but was NOT prepared spanning-aware (e.g. an
// immediate prepare with no preview layout) do we rebuild from the committed spreads.
const forceRebuild = segment.spansToNextSpread === true && segment.spanningPlanPrepared !== true;
const texturePlan = this.textureRenderer.prepareRevealBlock(revealDetail, {
publishEvent: false,
forceRebuild: segment.spansToNextSpread === true
forceRebuild
});
segment.activeTexturePlan = texturePlan;
this.applyTexturePlan(texturePlan, segment, 'activate');