Fix timeline issues with event markers alignment

lib/ui/screens/timeline/timeline_screen.dart

@@ -1,6 +1,7 @@
 import 'dart:async';
 import 'dart:ui';
 
+import 'package:flutter/foundation.dart';
 import 'package:wonders/common_libs.dart';
 import 'package:wonders/logic/common/debouncer.dart';
 import 'package:wonders/logic/common/string_utils.dart';
@@ -22,6 +23,7 @@ part 'widgets/_scrolling_viewport.dart';
 part 'widgets/_scrolling_viewport_controller.dart';
 part 'widgets/_timeline_section.dart';
 part 'widgets/_year_markers.dart';
+part 'widgets/_animated_era_text.dart';
 
 class TimelineScreen extends StatefulWidget {
   final WonderType? type;
@@ -35,12 +37,15 @@ class TimelineScreen extends StatefulWidget {
 class _TimelineScreenState extends State<TimelineScreen> {
   /// Create a scroll controller that the top and bottom timelines can share
   final ScrollController _scroller = ScrollController();
+  final _year = ValueNotifier<int>(0);
+
+  void _handleViewportYearChanged(int value) => _year.value = value;
 
   @override
   Widget build(BuildContext context) {
     return LayoutBuilder(builder: (_, constraints) {
       // Determine min and max size of the timeline based on the size available to this widget
-      const double scrubberSize = 70;
+      const double scrubberSize = 80;
       const double minSize = 1200;
       const double maxSize = 5500;
       return Container(
@@ -53,27 +58,33 @@ class _TimelineScreenState extends State<TimelineScreen> {
 
               /// Vertically scrolling timeline, manages a ScrollController.
               Expanded(
-                child: Stack(
+                child: _ScrollingViewport(
-                  children: [
-                    /// The timeline content itself
-                    _ScrollingViewport(
                   scroller: _scroller,
                   minSize: minSize,
                   maxSize: maxSize,
                   selectedWonder: widget.type,
-                    ),
+                  onYearChanged: _handleViewportYearChanged,
-                  ],
                 ),
               ),
 
+              /// Era Text (classical, modern etc)
+              ValueListenableBuilder<int>(
+                valueListenable: _year,
+                builder: (_, value, __) => _AnimatedEraText(value),
+              ),
+              Gap($styles.insets.xs),
+
               /// Mini Horizontal timeline, reacts to the state of the larger scrolling timeline,
               /// and changes the timelines scroll position on Hz drag
-              _BottomScrubber(
+              Padding(
+                padding: EdgeInsets.symmetric(horizontal: $styles.insets.lg),
+                child: _BottomScrubber(
                   _scroller,
                   size: scrubberSize,
                   timelineMinSize: minSize,
                   selectedWonder: widget.type,
                 ),
+              ),
               Gap($styles.insets.lg),
             ],
           ),

lib/ui/screens/timeline/widgets/_animated_era_text.dart

@@ -0,0 +1,16 @@
+part of '../timeline_screen.dart';
+
+class _AnimatedEraText extends StatelessWidget {
+  const _AnimatedEraText(this.year);
+  final int year;
+
+  @override
+  Widget build(BuildContext context) {
+    String era = StringUtils.getEra(year);
+    final style = $styles.text.body.copyWith(color: $styles.colors.offWhite);
+    return Semantics(
+      liveRegion: true,
+      child: Text(era, style: style),
+    ).animate(key: ValueKey(era)).fadeIn().slide(begin: Offset(0, .2));
+  }
+}

lib/ui/screens/timeline/widgets/_bottom_scrubber.dart

@@ -41,8 +41,12 @@ class _BottomScrubber extends StatelessWidget {
       child: Stack(
         children: [
           /// Timeline background
-          Padding(
+          Container(
-            padding: EdgeInsets.all($styles.insets.sm),
+            padding: EdgeInsets.all($styles.insets.md),
+            decoration: BoxDecoration(
+              color: $styles.colors.greyStrong,
+              borderRadius: BorderRadius.circular($styles.corners.md),
+            ),
             child: WondersTimelineBuilder(
               crossAxisGap: 4,
               selectedWonders: selectedWonder != null ? [selectedWonder!] : [],

lib/ui/screens/timeline/widgets/_dashed_divider_with_year.dart

@@ -30,6 +30,7 @@ class _DashedDividerWithYear extends StatelessWidget {
                       shadows: $styles.shadows.textStrong,
                     ),
                   ),
+                  Gap($styles.insets.xs),
                 ],
               ),
             ),

lib/ui/screens/timeline/widgets/_event_markers.dart

@@ -13,6 +13,7 @@ class _EventMarkers extends StatefulWidget {
 }
 
 class _EventMarkersState extends State<_EventMarkers> {
+  bool get showReferenceMarkers => kDebugMode;
   int get startYr => wondersLogic.timelineStartYear;
 
   int get endYr => wondersLogic.timelineEndYear;
@@ -60,7 +61,7 @@ class _EventMarkersState extends State<_EventMarkers> {
 
         /// Create a marker for each event
         List<Widget> markers = timelineLogic.events.map((event) {
-          final offsetY = _calculateOffsetY(event.year);
+          double offsetY = _calculateOffsetY(event.year);
           return _EventMarker(offsetY,
               isSelected: event == selectedEvent, semanticLabel: '${event.year}: ${event.description}');
         }).toList();
@@ -73,13 +74,33 @@ class _EventMarkersState extends State<_EventMarkers> {
             padding: EdgeInsets.only(left: 75),
             child: SizedBox(
               width: 20,
-              child: Stack(children: markers),
+              child: Stack(
+                children: [
+                  ...markers,
+                  if (showReferenceMarkers) ..._buildReferenceMarkers(),
+                ],
+              ),
             ),
           ),
         );
       }),
     );
   }
+
+  List<Widget> _buildReferenceMarkers() {
+    final marker = Container(color: Colors.red.withOpacity(.4), width: 10, height: 10);
+    return [
+      Align(
+        alignment: Alignment.topCenter,
+        child: FractionalTranslation(translation: Offset(0, -.5), child: marker),
+      ),
+      Align(alignment: Alignment.center, child: marker),
+      Align(
+        alignment: Alignment.bottomCenter,
+        child: FractionalTranslation(translation: Offset(0, .5), child: marker),
+      ),
+    ];
+  }
 }
 
 /// A dot that represents a single global event.
@@ -99,6 +120,12 @@ class _EventMarker extends StatelessWidget {
   Widget build(BuildContext context) {
     return Align(
       alignment: Alignment(0, -1 + offset * 2),
+      // Use an OverflowBox wrapped in a zero-height sized box so that al
+      // This allows alignment-based positioning to be accurate even at the edges of the parent.
+      child: SizedBox(
+        height: 0,
+        child: OverflowBox(
+          maxHeight: 30,
           child: Semantics(
             label: semanticLabel,
             child: Container(
@@ -120,6 +147,8 @@ class _EventMarker extends StatelessWidget {
               ),
             ),
           ),
+        ),
+      ),
     );
   }
 }

lib/ui/screens/timeline/widgets/_scrolling_viewport.dart

@@ -9,11 +9,13 @@ class _ScrollingViewport extends StatefulWidget {
     required this.minSize,
     required this.maxSize,
     required this.selectedWonder,
+    this.onYearChanged,
   }) : super(key: key);
   final double minSize;
   final double maxSize;
   final ScrollController scroller;
   final WonderType? selectedWonder;
+  final void Function(int year)? onYearChanged;
   final void Function(_ScrollingViewportController controller)? onInit;
 
   @override
@@ -53,21 +55,10 @@ class _ScalingViewportState extends State<_ScrollingViewport> {
       // Fade in entire view when first shown
       child: Stack(
         children: [
-          Column(
+          // Main content area
-            children: [
+          _buildScrollingArea(context).animate().fadeIn(),
-              /// Main scrolling area, holds the year markers, and the [WondersTimelineBuilder]
-              Expanded(
-                child: _buildScrollingArea(context),
-              ),
-              Gap($styles.insets.xs),
 
-              /// Era Text (classical, modern etc)
+          // Dashed line with a year that changes as we scroll
-              _buildAnimatedEraText(context),
-              Gap($styles.insets.xs),
-            ],
-          ).animate().fadeIn(),
-
-          /// Dashed line with a year that changes as we scroll
           IgnorePointer(
             ignoringSemantics: false,
             child: AnimatedBuilder(
@@ -82,23 +73,6 @@ class _ScalingViewportState extends State<_ScrollingViewport> {
     );
   }
 
-  AnimatedBuilder _buildAnimatedEraText(BuildContext context) {
-    return AnimatedBuilder(
-        animation: controller.scroller,
-        builder: (_, __) {
-          String era = StringUtils.getEra(controller.calculateYearFromScrollPos());
-          final style = $styles.text.body.copyWith(color: $styles.colors.offWhite);
-          return AnimatedSwitcher(
-            duration: $styles.times.fast,
-            child: Semantics(
-                liveRegion: true,
-                child: Text(era, key: ValueKey(era), style: style)
-                    .animate(key: ValueKey(era))
-                    .slide(begin: Offset(0, .2))),
-          );
-        });
-  }
-
   Widget _buildScrollingArea(BuildContext context) {
     // Builds a TimelineSection, and passes it the currently selected yr based on scroll position.
     // Rebuilds when timeline is scrolled.

lib/ui/screens/timeline/widgets/_scrolling_viewport_controller.dart

@@ -12,6 +12,10 @@ class _ScrollingViewportController extends ChangeNotifier {
   late BoxConstraints _constraints;
   _ScrollingViewport get widget => state.widget;
   ScrollController get scroller => widget.scroller;
+  late final ValueNotifier<int> _currentYr = ValueNotifier(startYr)
+    ..addListener(
+      () => state.widget.onYearChanged?.call(_currentYr.value),
+    );
 
   void init() {
     scheduleMicrotask(() {
@@ -22,10 +26,13 @@ class _ScrollingViewportController extends ChangeNotifier {
         final pos = calculateScrollPosFromYear(data.startYr);
         scroller.jumpTo(pos - 200);
         scroller.animateTo(pos, duration: 1.35.seconds, curve: Curves.easeOutCubic);
+        scroller.addListener(_updateCurrentYear);
       }
     });
   }
 
+  void _updateCurrentYear() => _currentYr.value = calculateYearFromScrollPos();
+
   /// Allows ancestors to set zoom directly
   void setZoom(double d) {
     // ignore: invalid_use_of_protected_member

lib/ui/screens/timeline/widgets/_year_markers.dart

@@ -57,11 +57,22 @@ class _YearMarker extends StatelessWidget {
     return ExcludeSemantics(
       child: Align(
         alignment: Alignment(0, -1 + offset * 2),
+
+        // Use an OverflowBox wrapped in a zero-height sized box so that al
+        // This allows alignment-based positioning to be accurate even at the edges of the parent.
+        child: SizedBox(
+          height: 0,
+          child: OverflowBox(
+            alignment: Alignment.topCenter,
+            maxHeight: 100,
+            maxWidth: 100,
             child: FractionalTranslation(
-          translation: Offset(0, 0),
+                translation: Offset(0, -.5),
-          child: Text('${yr.abs()}', style: $styles.text.body.copyWith(color: Colors.white, height: 1)),
+                child: Text('${yr.abs()}', style: $styles.text.body.copyWith(color: Colors.white, height: 1))),
           ),
         ),
+        //child:,
+      ),
     );
   }
 }