perf: 降低全公車地圖動畫重建成本

lib/screens/bus_map_screen.dart

@@ -854,14 +854,7 @@ class _BusMapScreenState extends State<BusMapScreen>
 
     final map = _unsupported
         ? _buildUnsupportedNotice(theme)
-        : ValueListenableBuilder<int>(
-            valueListenable: _animationTick,
-            builder: (context, _, _) => _buildMap(
-              theme,
-              drawSet,
-              controller.settings.mobileMapProvider,
-            ),
-          );
+        : _buildMap(theme, drawSet, controller.settings.mobileMapProvider);
 
     final overlay = Stack(
       children: [
@@ -1237,14 +1230,19 @@ class _BusMapScreenState extends State<BusMapScreen>
     MobileMapProvider mapProvider,
   ) {
     if (useGoogleMapsProviderFor(mapProvider)) {
-      return _buildGoogleMap(theme, drawSet);
+      // google_maps_flutter updates markers through widget configuration, so
+      // its map still needs the animation tick. The FlutterMap backend below
+      // can isolate ticks to one marker layer instead of rebuilding the map.
+      return ValueListenableBuilder<int>(
+        valueListenable: _animationTick,
+        builder: (context, _, _) => _buildGoogleMap(theme, drawSet),
+      );
     }
     return _buildFlutterMap(theme, drawSet);
   }
 
   Widget _buildFlutterMap(ThemeData theme, _BusMapDrawSet drawSet) {
     final buses = drawSet.buses;
-    final now = DateTime.now();
     final geometry = _selectedGeometry;
     return FlutterMap(
       mapController: _mapController,
@@ -1346,7 +1344,16 @@ class _BusMapScreenState extends State<BusMapScreen>
                 ),
             ],
           ),
-        MarkerLayer(markers: _osmBusMarkers(buses, now)),
+        // A selected route animates four times per second. Keep that hot
+        // rebuild below FlutterMap so tiles, route geometry, stop pins and
+        // clusters remain untouched between server snapshots.
+        ValueListenableBuilder<int>(
+          valueListenable: _animationTick,
+          builder: (context, _, _) => MarkerLayer(
+            key: const ValueKey('bus-map-moving-marker-layer'),
+            markers: _osmBusMarkers(buses, DateTime.now()),
+          ),
+        ),
       ],
     );
   }

test/bus_map_screen_test.dart

@@ -648,6 +648,48 @@ void main() {
     expect(after.longitude, greaterThan(before.longitude));
   });
 
+  _mapTest('animation ticks rebuild only the moving marker layer', (
+    tester,
+    log,
+    controller,
+  ) async {
+    await _pumpMap(tester, controller);
+    await _pumpUntil(
+      tester,
+      () => find.byType(BusMapBusMarker).evaluate().length == 2,
+    );
+    await _selectTheResolvedBus(tester, log);
+
+    final mapBefore = tester.widget<FlutterMap>(find.byType(FlutterMap));
+    final tileLayerBefore = tester.widget<TileLayer>(find.byType(TileLayer));
+    final movingLayerBefore = tester.widget<MarkerLayer>(
+      find.byKey(const ValueKey('bus-map-moving-marker-layer')),
+    );
+
+    await tester.pump(const Duration(milliseconds: 300));
+
+    expect(
+      identical(tester.widget<FlutterMap>(find.byType(FlutterMap)), mapBefore),
+      isTrue,
+    );
+    expect(
+      identical(
+        tester.widget<TileLayer>(find.byType(TileLayer)),
+        tileLayerBefore,
+      ),
+      isTrue,
+    );
+    expect(
+      identical(
+        tester.widget<MarkerLayer>(
+          find.byKey(const ValueKey('bus-map-moving-marker-layer')),
+        ),
+        movingLayerBefore,
+      ),
+      isFalse,
+    );
+  });
+
   _mapTest('a bus the feed could not pin down is still named', (
     tester,
     log,