roll home screen performance tweaks to library screens

src/activities/home/MyLibraryActivity.cpp

@@ -13,6 +13,9 @@
 #include "fontIds.h"
 #include "util/StringUtils.h"
 
+// Static thumbnail existence cache definition
+ThumbExistsCache MyLibraryActivity::thumbExistsCache[MyLibraryActivity::MAX_THUMB_CACHE];
+
 namespace {
 // Layout constants
 constexpr int TAB_BAR_Y = 15;
@@ -510,15 +513,45 @@ void MyLibraryActivity::renderRecentTab() const {
     const int y = CONTENT_START_Y + (i % pageItems) * RECENTS_LINE_HEIGHT;
     const bool isSelected = (i == selectorIndex);
 
-    // Try to load and draw micro-thumbnail
+    // Try to load and draw micro-thumbnail (with existence caching)
-    const std::string microThumbPath = getMicroThumbPathForBook(book.path);
     bool hasThumb = false;
-    if (!microThumbPath.empty() && SdMan.exists(microThumbPath.c_str())) {
+
+    // Check if we have cached existence info for this book
+    ThumbExistsCache* existsCache = nullptr;
+    std::string microThumbPath;
+    bool thumbExists = false;
+    bool existsCacheHit = false;
+
+    if (i < MAX_THUMB_CACHE) {
+      existsCache = &thumbExistsCache[i];
+      if (existsCache->checked && existsCache->bookPath == book.path) {
+        // Use cached existence info
+        existsCacheHit = true;
+        thumbExists = existsCache->exists;
+        microThumbPath = existsCache->thumbPath;
+      }
+    }
+
+    // If not cached, check existence and cache the result
+    if (!existsCacheHit) {
+      microThumbPath = getMicroThumbPathForBook(book.path);
+      thumbExists = !microThumbPath.empty() && SdMan.exists(microThumbPath.c_str());
+
+      // Cache the result
+      if (existsCache != nullptr) {
+        existsCache->bookPath = book.path;
+        existsCache->thumbPath = microThumbPath;
+        existsCache->exists = thumbExists;
+        existsCache->checked = true;
+      }
+    }
+
+    // Load and render thumbnail if it exists
+    if (thumbExists) {
       FsFile thumbFile;
       if (SdMan.openFileForRead("MYL", microThumbPath, thumbFile)) {
         Bitmap bitmap(thumbFile);
         if (bitmap.parseHeaders() == BmpReaderError::Ok) {
-          // Calculate actual drawn size (scaled to fit within max dimensions, preserving aspect ratio)
           const int bmpW = bitmap.getWidth();
           const int bmpH = bitmap.getHeight();
           const float scaleX = static_cast<float>(MICRO_THUMB_WIDTH) / static_cast<float>(bmpW);
@@ -527,10 +560,7 @@ void MyLibraryActivity::renderRecentTab() const {
           const int drawnW = static_cast<int>(bmpW * scale);
           const int drawnH = static_cast<int>(bmpH * scale);
 
-          // Center thumbnail vertically within the row using actual drawn height
           const int thumbY = y + (RECENTS_LINE_HEIGHT - drawnH) / 2;
-          // When selected, clear only the actual drawn area to white first
-          // (drawBitmap1Bit only draws pixels, it doesn't clear, so we need the white background)
           if (isSelected) {
             renderer.fillRect(thumbX, thumbY, drawnW, drawnH, false);
           }

src/activities/home/MyLibraryActivity.h

@@ -10,6 +10,14 @@
 #include "../Activity.h"
 #include "RecentBooksStore.h"
 
+// Cached thumbnail existence info for Recent tab
+struct ThumbExistsCache {
+  std::string bookPath;      // Book path this cache entry belongs to
+  std::string thumbPath;     // Path to micro-thumbnail (if exists)
+  bool checked = false;      // Whether we've checked for this book
+  bool exists = false;       // Whether thumbnail exists
+};
+
 class MyLibraryActivity final : public Activity {
  public:
   enum class Tab { Recent, Files };
@@ -35,6 +43,10 @@ class MyLibraryActivity final : public Activity {
   // Recent tab state
   std::vector<RecentBook> recentBooks;
 
+  // Static thumbnail existence cache - persists across activity enter/exit
+  static constexpr int MAX_THUMB_CACHE = 10;
+  static ThumbExistsCache thumbExistsCache[MAX_THUMB_CACHE];
+
   // Files tab state (from FileSelectionActivity)
   std::string basepath = "/";
   std::vector<std::string> files;