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Add paragraph index LUT for accurate KOReader position sync

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Store per-page paragraph indices in section cache to enable precise
XPath-to-page and page-to-XPath mapping without reparsing XHTML.

Forward path (upload): generates XPath directly from paragraph LUT
instead of byte-offset estimation, eliminating drift in chapters
with non-uniform content density.

Reverse path (download): resolves incoming KOReader XPath p[N] to
the exact page via paragraph LUT lookup.

Paragraph counter counts all <p> elements including display:none
to match ChapterXPathIndexer and crengine's standard XPath counting.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
This commit is contained in:
jpirnay
2026-03-22 12:29:30 +01:00
co-authored by Claude Opus 4.6
parent 5b710e960f
commit fd70b3a231
17 changed files with 354 additions and 43 deletions
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lib/KOReaderSync/ProgressMapper.cpp
+17 -6
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@@ -19,12 +19,17 @@ KOReaderPosition ProgressMapper::toKOReader(const std::shared_ptr<Epub>& epub, c
// Calculate overall book progress (0.0-1.0)
result.percentage = epub->calculateProgress(pos.spineIndex, intraSpineProgress);
// Generate the best available XPath for the current chapter position.
// Prefer element-level XPaths from a lightweight XHTML reparse; fall back
// to a synthetic chapter-level path if parsing fails.
result.xpath = ChapterXPathIndexer::findXPathForProgress(epub, pos.spineIndex, intraSpineProgress);
if (result.xpath.empty()) {
result.xpath = generateXPath(pos.spineIndex);
// Generate XPath for the current position.
// Prefer paragraph index from the section cache LUT (exact element mapping) over
// byte-offset estimation (which can drift in chapters with non-uniform content density).
if (pos.hasParagraphIndex && pos.paragraphIndex > 0) {
result.xpath = "/body/DocFragment[" + std::to_string(pos.spineIndex + 1) + "]/body/p[" +
std::to_string(pos.paragraphIndex) + "]";
} else {
result.xpath = ChapterXPathIndexer::findXPathForProgress(epub, pos.spineIndex, intraSpineProgress);
if (result.xpath.empty()) {
result.xpath = generateXPath(pos.spineIndex);
}
}
// Get chapter info for logging
@@ -64,6 +69,12 @@ CrossPointPosition ProgressMapper::toCrossPoint(const std::shared_ptr<Epub>& epu
resolvedIntraSpineProgress = intraFromXPath;
usedXPathMapping = true;
}
// Extract paragraph index from XPath for direct page lookup via section cache
uint16_t pIndex = 0;
if (ChapterXPathIndexer::tryExtractParagraphIndexFromXPath(koPos.xpath, pIndex)) {
result.paragraphIndex = pIndex;
result.hasParagraphIndex = true;
}
}
if (!usedXPathMapping) {