Prefetch modes: Off / Adjacent (4 cardinals) / Full page (spiral)

- Off: no prefetching
- Adjacent: simultaneous left/right/up/down (4 posts)
- Full page: ring expansion in all 8 directions
Dropdown in Settings > General replaces the old checkbox.

booru_viewer/gui/app.py

@@ -845,7 +845,7 @@ class BooruApp(QMainWindow):
         self._grid.setFocus()
 
         # Start prefetching from top of page
-        if self._db.get_setting_bool("prefetch_adjacent") and posts:
+        if self._db.get_setting("prefetch_mode") in ("Adjacent", "Full page") and posts:
             self._prefetch_adjacent(0)
 
         # Infinite scroll: if first page doesn't fill viewport, load more
@@ -912,7 +912,7 @@ class BooruApp(QMainWindow):
             # All done — unlock loading, evict, prefetch
             self._loading = False
             self._auto_evict_cache()
-            if self._db.get_setting_bool("prefetch_adjacent"):
+            if self._db.get_setting("prefetch_mode") in ("Adjacent", "Full page"):
                 self._prefetch_adjacent(idx)
             # Check if still at bottom or content doesn't fill viewport
             sb = self._grid.verticalScrollBar()
@@ -1000,37 +1000,45 @@ class BooruApp(QMainWindow):
             self._run_async(_load)
 
             # Prefetch adjacent posts
-            if self._db.get_setting_bool("prefetch_adjacent"):
+            if self._db.get_setting("prefetch_mode") in ("Adjacent", "Full page"):
                 self._prefetch_adjacent(index)
 
     def _prefetch_adjacent(self, index: int) -> None:
-        """Prefetch outward from clicked post in all directions, covering the whole page."""
+        """Prefetch posts around the given index."""
         total = len(self._posts)
         if total == 0:
             return
         cols = self._grid._flow.columns
+        mode = self._db.get_setting("prefetch_mode")
 
-        # Build ring order: at each distance, grab all 8 directions
-        seen = {index}
-        order = []
-        for dist in range(1, total):
-            ring = set()
-            for dy in (-dist, 0, dist):
-                for dx in (-dist, 0, dist):
-                    if dy == 0 and dx == 0:
-                        continue
-                    adj = index + dy * cols + dx
+        if mode == "Adjacent":
+            # Just 4 cardinals: left, right, up, down
+            order = []
+            for offset in [1, -1, cols, -cols]:
+                adj = index + offset
+                if 0 <= adj < total:
+                    order.append(adj)
+        else:
+            # Full page: ring expansion in all 8 directions
+            seen = {index}
+            order = []
+            for dist in range(1, total):
+                ring = set()
+                for dy in (-dist, 0, dist):
+                    for dx in (-dist, 0, dist):
+                        if dy == 0 and dx == 0:
+                            continue
+                        adj = index + dy * cols + dx
+                        if 0 <= adj < total and adj not in seen:
+                            ring.add(adj)
+                for adj in (index + dist, index - dist):
                     if 0 <= adj < total and adj not in seen:
                         ring.add(adj)
-            # Also add pure linear neighbors for non-grid nav
-            for adj in (index + dist, index - dist):
-                if 0 <= adj < total and adj not in seen:
-                    ring.add(adj)
-            for adj in sorted(ring):
-                seen.add(adj)
-                order.append(adj)
-            if len(order) >= total - 1:
-                break
+                for adj in sorted(ring):
+                    seen.add(adj)
+                    order.append(adj)
+                if len(order) >= total - 1:
+                    break
 
         async def _prefetch_spiral():
             for adj in order:

booru_viewer/gui/settings.py

@@ -111,9 +111,13 @@ class SettingsDialog(QDialog):
         form.addRow("", self._preload)
 
         # Prefetch adjacent posts
-        self._prefetch = QCheckBox("Prefetch whole page over time")
-        self._prefetch.setChecked(self._db.get_setting_bool("prefetch_adjacent"))
-        form.addRow("", self._prefetch)
+        self._prefetch_combo = QComboBox()
+        self._prefetch_combo.addItems(["Off", "Adjacent", "Full page"])
+        prefetch_mode = self._db.get_setting("prefetch_mode") or "Off"
+        idx = self._prefetch_combo.findText(prefetch_mode)
+        if idx >= 0:
+            self._prefetch_combo.setCurrentIndex(idx)
+        form.addRow("Prefetch:", self._prefetch_combo)
 
         # Infinite scroll
         self._infinite_scroll = QCheckBox("Infinite scroll (replaces page buttons)")
@@ -681,7 +685,7 @@ class SettingsDialog(QDialog):
         self._db.set_setting("default_rating", self._default_rating.currentText())
         self._db.set_setting("default_score", str(self._default_score.value()))
         self._db.set_setting("preload_thumbnails", "1" if self._preload.isChecked() else "0")
-        self._db.set_setting("prefetch_adjacent", "1" if self._prefetch.isChecked() else "0")
+        self._db.set_setting("prefetch_mode", self._prefetch_combo.currentText())
         self._db.set_setting("infinite_scroll", "1" if self._infinite_scroll.isChecked() else "0")
         self._db.set_setting("slideshow_monitor", self._monitor_combo.currentText())
         self._db.set_setting("library_dir", self._library_dir.text().strip())