perf: skip redundant progress writes when position is unchanged (#2436)

Co-authored-by: Erica Jensen <erica@mailershaven.com>
Co-authored-by: Uri Tauber <uritaube@gmail.com>

src/activities/reader/EpubReaderActivity.h

@@ -63,6 +63,12 @@ class EpubReaderActivity final : public Activity {
   SavedPosition savedPositions[MAX_FOOTNOTE_DEPTH] = {};
   int footnoteDepth = 0;
 
+  // Last position persisted by render()'s saveProgress, used to skip redundant
+  // writeAtomic calls on no-op re-renders (menu/bookmark/screenshot).
+  int lastSavedSpineIndex = -1;
+  int lastSavedPage = -1;
+  int lastSavedPageCount = -1;
+
   void renderContents(std::unique_ptr<Page> page, int orientedMarginTop, int orientedMarginRight,
                       int orientedMarginBottom, int orientedMarginLeft);
   void renderStatusBar() const;