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Fix koreader sync regresssion

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This commit is contained in:
jpirnay
2026-05-23 13:20:01 +02:00
parent 6717c02173
commit ff93b152a3
6 changed files with 390 additions and 127 deletions
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lib/KOReaderSync/ChapterXPathForwardMapper.cpp
+49 -41
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@@ -19,14 +19,24 @@ namespace {
// Strategy:
// 1) Count total visible text bytes in chapter.
// 2) Stream parse again and stop when target byte offset is reached.
// 3) Emit /text()[N].M relative to the deepest open element so KOReader can
// place the cursor at character precision regardless of nesting depth.
// 3) Emit either /text()[N].M when the cursor is at a direct text child of
// <body>, or the bare element path otherwise.
//
// Text-node counting matches KOReader/crengine: the Nth XML text node within
// an element, including whitespace-only nodes (those are still real DOM text
// nodes). Empty (len=0) text isn't emitted by expat at all, which mirrors
// KOReader's behavior of skipping the empty text nodes that bare
// <a id="anchor"/> elements would otherwise produce.
// Why body-level only (and not deep nested /p[i]/span[j]/text()[k].M):
// KOReader's crengine normalises the DOM differently than expat — it merges
// adjacent inline elements, drops empty wrappers, and renumbers text nodes
// inside <p>/<span>/<em>. A deep XPath we emit (e.g. /p[17]/span[1]/text()[1].26)
// often fails to match crengine's tree, and KOReader stores a degraded
// fallback position (start-of-wrapper-div or off-by-N text node) that
// round-trips back to the wrong page on pull. Body-level text-point XPaths
// have a much higher round-trip success rate even though they sacrifice
// character-precision inside paragraphs. The Section paragraph LUT then
// snaps the pulled position to the correct page anyway, so the precision
// loss is invisible to users.
//
// This matches the 1.42 behavior. The pre-1.43 forward mapper only emitted
// text-point XPaths when the cursor was a direct text child of <body>; the
// 1.43 change to deep emission is the regression we're undoing here.
struct ForwardState : StackState {
int spineIndex;
@@ -35,32 +45,24 @@ struct ForwardState : StackState {
bool found = false;
XML_Parser parser = nullptr;
// Per-element text-node bookkeeping. Mirrors `stack` 1:1 — every push/pop
// appends/removes a counter so the top of the stack always refers to the
// currently open element. `pendingTextNode` is set after every element
// boundary so the next char data starts a fresh text node within whatever
// element is currently on top.
std::vector<int> textNodeIndexStack;
std::vector<size_t> codepointsInTextNodeStack;
bool pendingTextNode = true;
// Body-level text-node bookkeeping: only counts text nodes that are direct
// children of <body>. Inline-element text contributes to totalTextBytes via
// the StackState base, but does not advance bodyTextNodeCount because
// KOReader can't round-trip a deep text-node XPath reliably.
int bodyTextNodeCount = 0;
size_t codepointsInBodyTextNode = 0;
bool inBodyTextNode = false;
ForwardState(const int spineIndex, const size_t targetOffset) : spineIndex(spineIndex), targetOffset(targetOffset) {
textNodeIndexStack.reserve(32);
codepointsInTextNodeStack.reserve(32);
}
ForwardState(const int spineIndex, const size_t targetOffset) : spineIndex(spineIndex), targetOffset(targetOffset) {}
void onStartElement(const XML_Char* rawName) {
inBodyTextNode = false;
pushElement(rawName);
textNodeIndexStack.push_back(0);
codepointsInTextNodeStack.push_back(0);
pendingTextNode = true;
}
void onEndElement() {
inBodyTextNode = false;
popElement();
if (!textNodeIndexStack.empty()) textNodeIndexStack.pop_back();
if (!codepointsInTextNodeStack.empty()) codepointsInTextNodeStack.pop_back();
pendingTextNode = true;
}
void onCharData(const XML_Char* text, const int len) {
@@ -68,30 +70,34 @@ struct ForwardState : StackState {
return;
}
if (pendingTextNode) {
if (!textNodeIndexStack.empty()) textNodeIndexStack.back()++;
if (!codepointsInTextNodeStack.empty()) codepointsInTextNodeStack.back() = 0;
pendingTextNode = false;
const bool atBodyLevel = bodyIdx() + 1 == static_cast<int>(stack.size());
if (atBodyLevel && !inBodyTextNode) {
inBodyTextNode = true;
bodyTextNodeCount++;
codepointsInBodyTextNode = 0;
}
const size_t cpCount = countUtf8Codepoints(text, len);
if (isWhitespaceOnly(text, len)) {
if (!codepointsInTextNodeStack.empty()) codepointsInTextNodeStack.back() += cpCount;
if (atBodyLevel) {
codepointsInBodyTextNode += countUtf8Codepoints(text, len);
}
return;
}
const size_t visible = countVisibleBytes(text, len);
if (totalTextBytes + visible >= targetOffset) {
const int textNode = textNodeIndexStack.empty() ? 0 : textNodeIndexStack.back();
const size_t cpsInNode = codepointsInTextNodeStack.empty() ? 0 : codepointsInTextNodeStack.back();
// KOReader/crengine text-point semantics use codepoint offsets.
const size_t targetVisibleByteInChunk = targetOffset - totalTextBytes;
const size_t cpInChunk = codepointAtVisibleByte(text, len, targetVisibleByteInChunk);
const size_t charOff = cpsInNode + cpInChunk;
if (textNode > 0) {
result = currentXPath(spineIndex) + "/text()[" + std::to_string(textNode) + "]." + std::to_string(charOff);
if (atBodyLevel && bodyTextNodeCount > 0) {
// KOReader/crengine text-point semantics use codepoint offsets.
const size_t targetVisibleByteInChunk = targetOffset - totalTextBytes;
const size_t cpInChunk = codepointAtVisibleByte(text, len, targetVisibleByteInChunk);
const size_t charOff = codepointsInBodyTextNode + cpInChunk;
result =
currentXPath(spineIndex) + "/text()[" + std::to_string(bodyTextNodeCount) + "]." + std::to_string(charOff);
} else {
// Cursor is inside a nested element. Emit the element path without a
// text-point suffix — KOReader will treat this as a position at the
// start of the named element, which is good enough for paragraph-level
// accuracy. Don't emit a deep text() index here: see header comment.
result = currentXPath(spineIndex);
}
found = true;
@@ -102,7 +108,9 @@ struct ForwardState : StackState {
}
totalTextBytes += visible;
if (!codepointsInTextNodeStack.empty()) codepointsInTextNodeStack.back() += cpCount;
if (atBodyLevel) {
codepointsInBodyTextNode += countUtf8Codepoints(text, len);
}
}
};