Shared debounce logic

mobile/lib/presentation/widgets/timeline/fixed/segment.model.dart

@@ -106,7 +106,7 @@ class _FixedSegmentRow extends ConsumerWidget {
 
   @override
   Widget build(BuildContext context, WidgetRef ref) {
-    final isScrubbing = ref.watch(timelineStateProvider.select((s) => s.isScrubbing));
+    final recommendDeferredLoading = ref.watch(timelineStateProvider.select((s) => s.recommendDeferredLoading));
     final timelineService = ref.read(timelineServiceProvider);
     final isDynamicLayout = columnCount <= (context.isMobile ? 2 : 3);
 
@@ -119,7 +119,7 @@ class _FixedSegmentRow extends ConsumerWidget {
       );
     }
 
-    if (isScrubbing) {
+    if (recommendDeferredLoading) {
       return _buildPlaceholder(context);
     }
 

mobile/lib/presentation/widgets/timeline/scrubber.widget.dart

@@ -11,7 +11,6 @@ import 'package:immich_mobile/presentation/widgets/timeline/constants.dart';
 import 'package:immich_mobile/presentation/widgets/timeline/segment.model.dart';
 import 'package:immich_mobile/presentation/widgets/timeline/timeline.state.dart';
 import 'package:immich_mobile/providers/haptic_feedback.provider.dart';
-import 'package:immich_mobile/utils/debounce.dart';
 import 'package:intl/intl.dart' hide TextDirection;
 
 /// A widget that will display a BoxScrollView with a ScrollThumb that can be dragged
@@ -89,8 +88,6 @@ class ScrubberState extends ConsumerState<Scrubber> with TickerProviderStateMixi
   bool _isDragging = false;
   List<_Segment> _segments = [];
   int _monthCount = 0;
-  DateTime? _currentScrubberDate;
-  Debouncer? _scrubberDebouncer;
 
   late AnimationController _thumbAnimationController;
   Timer? _fadeOutTimer;
@@ -145,7 +142,6 @@ class ScrubberState extends ConsumerState<Scrubber> with TickerProviderStateMixi
     _thumbAnimationController.dispose();
     _labelAnimationController.dispose();
     _fadeOutTimer?.cancel();
-    _scrubberDebouncer?.dispose();
     super.dispose();
   }
 
@@ -189,24 +185,6 @@ class ScrubberState extends ConsumerState<Scrubber> with TickerProviderStateMixi
     return false;
   }
 
-  void _onScrubberDateChanged(DateTime date) {
-    if (_currentScrubberDate != date) {
-      // Date changed, immediately set scrubbing to true
-      _currentScrubberDate = date;
-      ref.read(timelineStateProvider.notifier).setScrubbing(true);
-
-      // Initialize debouncer if needed
-      _scrubberDebouncer ??= Debouncer(interval: const Duration(milliseconds: 50));
-
-      // Debounce setting scrubbing to false
-      _scrubberDebouncer!.run(() {
-        if (_currentScrubberDate == date) {
-          ref.read(timelineStateProvider.notifier).setScrubbing(false);
-        }
-      });
-    }
-  }
-
   void _onDragStart(DragStartDetails _) {
     setState(() {
       _isDragging = true;
@@ -237,11 +215,6 @@ class ScrubberState extends ConsumerState<Scrubber> with TickerProviderStateMixi
       if (_lastLabel != label) {
         ref.read(hapticFeedbackProvider.notifier).selectionClick();
         _lastLabel = label;
-
-        // Notify timeline state of the new scrubber date position
-        if (_monthCount >= kMinMonthsToEnableScrubberSnap) {
-          _onScrubberDateChanged(nearestMonthSegment.date);
-        }
       }
     }
 
@@ -349,13 +322,6 @@ class ScrubberState extends ConsumerState<Scrubber> with TickerProviderStateMixi
       _isDragging = false;
     });
 
-    ref.read(timelineStateProvider.notifier).setScrubbing(false);
-
-    // Reset scrubber tracking when drag ends
-    _currentScrubberDate = null;
-    _scrubberDebouncer?.dispose();
-    _scrubberDebouncer = null;
-
     _resetThumbTimer();
   }
 

mobile/lib/presentation/widgets/timeline/timeline.state.dart

@@ -50,37 +50,43 @@ class TimelineArgs {
 }
 
 class TimelineState {
-  final bool isScrubbing;
   final bool isScrolling;
 
-  const TimelineState({this.isScrubbing = false, this.isScrolling = false});
+  /// Indicates whether the timeline is scrolling beyond some configured "high" speed,
+  /// such as when programmatically scrolling to the top or a really fast user fling
+  final bool recommendDeferredLoading;
 
-  bool get isInteracting => isScrubbing || isScrolling;
+  const TimelineState({this.isScrolling = false, this.recommendDeferredLoading = false});
+
+  bool get isInteracting => isScrolling || recommendDeferredLoading;
 
   @override
   bool operator ==(covariant TimelineState other) {
-    return isScrubbing == other.isScrubbing && isScrolling == other.isScrolling;
+    return isScrolling == other.isScrolling && recommendDeferredLoading == other.recommendDeferredLoading;
   }
 
   @override
-  int get hashCode => isScrubbing.hashCode ^ isScrolling.hashCode;
+  int get hashCode => isScrolling.hashCode ^ recommendDeferredLoading.hashCode;
 
-  TimelineState copyWith({bool? isScrubbing, bool? isScrolling}) {
-    return TimelineState(isScrubbing: isScrubbing ?? this.isScrubbing, isScrolling: isScrolling ?? this.isScrolling);
+  TimelineState copyWith({bool? isScrolling, bool? recommendDeferredLoading}) {
+    return TimelineState(
+      isScrolling: isScrolling ?? this.isScrolling,
+      recommendDeferredLoading: recommendDeferredLoading ?? this.recommendDeferredLoading,
+    );
   }
 }
 
 class TimelineStateNotifier extends Notifier<TimelineState> {
-  void setScrubbing(bool isScrubbing) {
-    state = state.copyWith(isScrubbing: isScrubbing);
-  }
-
   void setScrolling(bool isScrolling) {
     state = state.copyWith(isScrolling: isScrolling);
   }
 
+  void setRecommendDeferredLoading(bool recommendDeferredLoading) {
+    state = state.copyWith(recommendDeferredLoading: recommendDeferredLoading);
+  }
+
   @override
-  TimelineState build() => const TimelineState(isScrubbing: false, isScrolling: false);
+  TimelineState build() => const TimelineState(isScrolling: false, recommendDeferredLoading: false);
 }
 
 // This provider watches the buckets from the timeline service & args and serves the segments.

mobile/lib/presentation/widgets/timeline/timeline.widget.dart

@@ -25,6 +25,7 @@ import 'package:immich_mobile/providers/infrastructure/readonly_mode.provider.da
 import 'package:immich_mobile/providers/infrastructure/settings.provider.dart';
 import 'package:immich_mobile/providers/infrastructure/timeline.provider.dart';
 import 'package:immich_mobile/providers/timeline/multiselect.provider.dart';
+import 'package:immich_mobile/utils/debounce.dart';
 import 'package:immich_mobile/widgets/common/immich_sliver_app_bar.dart';
 import 'package:immich_mobile/widgets/common/mesmerizing_sliver_app_bar.dart';
 import 'package:immich_mobile/widgets/common/selection_sliver_app_bar.dart';
@@ -150,6 +151,8 @@ class _SliverTimelineState extends ConsumerState<_SliverTimeline> {
   double _baseScaleFactor = 3.0;
   int? _restoreAssetIndex;
 
+  final Debouncer _fastScrollDebouncer = Debouncer(interval: const Duration(milliseconds: 100));
+
   @override
   void initState() {
     super.initState();
@@ -182,11 +185,7 @@ class _SliverTimelineState extends ConsumerState<_SliverTimeline> {
     switch (event) {
       case ScrollToTopEvent():
         {
-          final timelineState = ref.read(timelineStateProvider.notifier);
-          timelineState.setScrubbing(true);
-          _scrollController
-              .animateTo(0, duration: const Duration(milliseconds: 250), curve: Curves.easeInOut)
-              .whenComplete(() => timelineState.setScrubbing(false));
+          _scrollController.animateTo(0, duration: const Duration(milliseconds: 250), curve: Curves.easeInOut);
         }
 
       case ScrollToDateEvent scrollToDateEvent:
@@ -246,13 +245,31 @@ class _SliverTimelineState extends ConsumerState<_SliverTimeline> {
 
   @override
   void dispose() {
+    _fastScrollDebouncer.dispose();
     _scrollController.dispose();
     _eventSubscription?.cancel();
     super.dispose();
   }
 
+  /// Track whether the timeline is moving fast enough to defer per-row asset loading
+  bool _onScrollVelocityNotification(ScrollNotification notification) {
+    // Only consider the primary timeline ScrollView (no nested views) and update events
+    if (notification.depth != 0 || notification is! ScrollUpdateNotification) {
+      return false;
+    }
+
+    // Use Flutter's built in fast velocity tracking
+    if (_scrollController.position.recommendDeferredLoading(context)) {
+      ref.read(timelineStateProvider.notifier).setRecommendDeferredLoading(true);
+
+      // We cannot rely on scroll end events, as the timeline scrubber jumps from position
+      // to position, resulting in large spikes in velocity followed by low velocity
+      _fastScrollDebouncer.run(() => ref.read(timelineStateProvider.notifier).setRecommendDeferredLoading(false));
+    }
+    return false;
+  }
+
   void _scrollToDate(DateTime date) {
-    final timelineState = ref.read(timelineStateProvider.notifier);
     final asyncSegments = ref.read(timelineSegmentProvider);
     asyncSegments.whenData((segments) {
       // Find the segment that contains assets from the target date
@@ -279,16 +296,11 @@ class _SliverTimelineState extends ConsumerState<_SliverTimeline> {
       if (fallbackSegment != null) {
         // Scroll to the segment with a small offset to show the header
         final targetOffset = fallbackSegment.startOffset - 50;
-        timelineState.setScrubbing(true);
-        _scrollController
-            .animateTo(
-              targetOffset.clamp(0.0, _scrollController.position.maxScrollExtent),
-              duration: const Duration(milliseconds: 500),
-              curve: Curves.easeInOut,
-            )
-            .whenComplete(() => timelineState.setScrubbing(false));
-      } else {
-        timelineState.setScrubbing(false);
+        _scrollController.animateTo(
+          targetOffset.clamp(0.0, _scrollController.position.maxScrollExtent),
+          duration: const Duration(milliseconds: 500),
+          curve: Curves.easeInOut,
+        );
       }
     });
   }
@@ -480,7 +492,10 @@ class _SliverTimelineState extends ConsumerState<_SliverTimeline> {
                   child: Stack(
                     clipBehavior: Clip.none,
                     children: [
-                      timeline,
+                      NotificationListener<ScrollNotification>(
+                        onNotification: _onScrollVelocityNotification,
+                        child: timeline,
+                      ),
                       if (isBottomWidgetVisible)
                         Positioned(
                           top: MediaQuery.paddingOf(context).top,