Picking up some itsthisjutin ideas

src/activities/reader/EpubReaderActivity.cpp

@@ -637,8 +637,26 @@ void EpubReaderActivity::launchKOReaderSync(const SyncLaunchMode mode) {
   sync.spineIndex = currentSpineIndex;
   sync.page = currentPage;
   sync.totalPagesInSpine = totalPages;
-  sync.paragraphIndex = 0;
-  sync.hasParagraphIndex = false;
+  // Populate paragraph index and XHTML seek hint from section LUT if available.
+  if (section) {
+    if (const auto pIdx = section->getParagraphIndexForPage(static_cast<uint16_t>(currentPage))) {
+      sync.paragraphIndex = *pIdx;
+      sync.hasParagraphIndex = true;
+      if (const auto hint = section->getXhtmlByteOffsetForPage(static_cast<uint16_t>(currentPage))) {
+        sync.xhtmlSeekHint = *hint;
+      } else {
+        sync.xhtmlSeekHint = 0;
+      }
+    } else {
+      sync.paragraphIndex = 0;
+      sync.hasParagraphIndex = false;
+      sync.xhtmlSeekHint = 0;
+    }
+  } else {
+    sync.paragraphIndex = 0;
+    sync.hasParagraphIndex = false;
+    sync.xhtmlSeekHint = 0;
+  }
   sync.intent = syncIntent;
   sync.outcome = KOReaderSyncOutcomeState::PENDING;
   sync.resultSpineIndex = 0;

src/activities/reader/KOReaderSyncActivity.cpp

@@ -651,8 +651,8 @@ bool KOReaderSyncActivity::computeLocalProgressAndChapter() {
     return false;
   }
 
-  CrossPointPosition localPos = {currentSpineIndex, currentPage, totalPagesInSpine, localParagraphIndex,
-                                 hasLocalParagraphIndex};
+  CrossPointPosition localPos = {currentSpineIndex,      currentPage,       totalPagesInSpine, localParagraphIndex,
+                                 hasLocalParagraphIndex, localXhtmlSeekHint};
   localProgress = ProgressMapper::toKOReader(epub, localPos);
 
   const int localTocIndex = epub->getTocIndexForSpineIndex(currentSpineIndex);

src/activities/reader/KOReaderSyncActivity.h

@@ -34,7 +34,7 @@ class KOReaderSyncActivity final : public Activity {
  public:
   explicit KOReaderSyncActivity(GfxRenderer& renderer, MappedInputManager& mappedInput, const std::string& epubPath,
                                 int currentSpineIndex, int currentPage, int totalPagesInSpine,
-                                uint16_t paragraphIndex = 0, bool hasParagraphIndex = false,
+                                uint16_t paragraphIndex = 0, bool hasParagraphIndex = false, uint32_t xhtmlSeekHint = 0,
                                 KOReaderSyncIntentState syncIntent = KOReaderSyncIntentState::COMPARE)
       : Activity("KOReaderSync", renderer, mappedInput),
         epubPath(epubPath),
@@ -43,6 +43,7 @@ class KOReaderSyncActivity final : public Activity {
         totalPagesInSpine(totalPagesInSpine),
         localParagraphIndex(paragraphIndex),
         hasLocalParagraphIndex(hasParagraphIndex),
+        localXhtmlSeekHint(xhtmlSeekHint),
         syncIntent(syncIntent),
         remoteProgress{},
         remotePosition{},
@@ -75,6 +76,7 @@ class KOReaderSyncActivity final : public Activity {
   int totalPagesInSpine;
   uint16_t localParagraphIndex;
   bool hasLocalParagraphIndex;
+  uint32_t localXhtmlSeekHint;
   KOReaderSyncIntentState syncIntent = KOReaderSyncIntentState::COMPARE;
 
   State state = WIFI_SELECTION;