fix: 2022 - no fling beyond the antimeridian if constrained

New file:
* `antimeridian.dart`: Testing if we can fling beyond the world. We can't, due to the constraint.

Impacted files:
* `camera_constraint.dart`
* `main.dart`: added new `AntimeridianPage` page.
* `map_interactive_viewer.dart`
* `menu_drawer.dart`

Author: monsieurtanuki

example/lib/main.dart

@@ -1,6 +1,7 @@
 import 'package:flutter/material.dart';
 import 'package:flutter_map_example/pages/abort_obsolete_requests.dart';
 import 'package:flutter_map_example/pages/animated_map_controller.dart';
+import 'package:flutter_map_example/pages/antimeridian.dart';
 import 'package:flutter_map_example/pages/bundled_offline_map.dart';
 import 'package:flutter_map_example/pages/circle.dart';
 import 'package:flutter_map_example/pages/debouncing_tile_update_transformer.dart';
@@ -55,6 +56,7 @@ class MyApp extends StatelessWidget {
         AbortObsoleteRequestsPage.route: (context) =>
             const AbortObsoleteRequestsPage(),
         PolylinePage.route: (context) => const PolylinePage(),
+        AntimeridianPage.route: (context) => const AntimeridianPage(),
         SingleWorldPolysPage.route: (context) => const SingleWorldPolysPage(),
         PolylinePerfStressPage.route: (context) =>
             const PolylinePerfStressPage(),

example/lib/pages/antimeridian.dart

@@ -0,0 +1,34 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_map/flutter_map.dart';
+import 'package:flutter_map_example/misc/tile_providers.dart';
+import 'package:flutter_map_example/widgets/drawer/menu_drawer.dart';
+import 'package:latlong2/latlong.dart';
+
+/// Testing if we can fling beyond the world. We can't, due to the constraint.
+class AntimeridianPage extends StatelessWidget {
+  static const String route = '/antimeridian';
+
+  const AntimeridianPage({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      appBar: AppBar(title: const Text('Antimeridian')),
+      drawer: const MenuDrawer(AntimeridianPage.route),
+      body: FlutterMap(
+        options: MapOptions(
+          initialZoom: 2,
+          cameraConstraint: CameraConstraint.contain(
+            bounds: LatLngBounds(
+              const LatLng(90, -180),
+              const LatLng(-90, 180),
+            ),
+          ),
+        ),
+        children: [
+          openStreetMapTileLayer,
+        ],
+      ),
+    );
+  }
+}

example/lib/widgets/drawer/menu_drawer.dart

@@ -5,6 +5,7 @@ import 'package:flutter/gestures.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_map_example/pages/abort_obsolete_requests.dart';
 import 'package:flutter_map_example/pages/animated_map_controller.dart';
+import 'package:flutter_map_example/pages/antimeridian.dart';
 import 'package:flutter_map_example/pages/bundled_offline_map.dart';
 import 'package:flutter_map_example/pages/circle.dart';
 import 'package:flutter_map_example/pages/debouncing_tile_update_transformer.dart';
@@ -147,6 +148,11 @@ class MenuDrawer extends StatelessWidget {
             routeName: PolylinePage.route,
             currentRoute: currentRoute,
           ),
+          MenuItemWidget(
+            caption: 'Antimeridian test',
+            routeName: AntimeridianPage.route,
+            currentRoute: currentRoute,
+          ),
           MenuItemWidget(
             caption: 'Circle Layer',
             routeName: CirclePage.route,

lib/src/gestures/map_interactive_viewer.dart

@@ -114,6 +114,7 @@ class MapInteractiveViewerState extends State<MapInteractiveViewer>
 
   late var _keyboardPanAnimationPrevZoom = _camera.zoom; // to detect changes
   late double _keyboardPanAnimationMaxVelocity;
+
   double _keyboardPanAnimationMaxVelocityCalculator(double zoom) =>
       _interactionOptions.keyboardOptions.maxPanVelocity?.call(zoom) ??
       5 * math.log(0.15 * zoom + 1) + 1;
@@ -124,7 +125,9 @@ class MapInteractiveViewerState extends State<MapInteractiveViewer>
 
   // Shortcuts
   MapCamera get _camera => widget.controller.camera;
+
   MapOptions get _options => widget.controller.options;
+
   InteractionOptions get _interactionOptions => _options.interactionOptions;
 
   @override
@@ -965,12 +968,15 @@ class MapInteractiveViewerState extends State<MapInteractiveViewer>
       newCenter = _camera.unprojectAtZoom(bestCenterPoint);
     }
 
-    widget.controller.moveRaw(
+    final moved = widget.controller.moveRaw(
       newCenter,
       _camera.zoom,
       hasGesture: true,
       source: MapEventSource.flingAnimationController,
     );
+    if (!moved) {
+      _closeFlingAnimationController(MapEventSource.flingAnimationController);
+    }
   }
 
   void _resetDoubleTapHold() {

lib/src/map/camera/camera_constraint.dart

@@ -142,7 +142,18 @@ class ContainCamera extends CameraConstraint {
       centerPix.dy.clamp(topOkCenter, botOkCenter),
     );
 
-    if (newCenterPix == centerPix) return camera;
+    if (newCenterPix == centerPix) {
+      return camera;
+    }
+
+    // Special case when the world is the limit: we want to stop at
+    // antimeridian lines.
+    // The standard test cannot work, as we'll always be in [-180,180].
+    // If the center changed, that means that the clamp did have an action.
+    // Therefore we went beyond the world.
+    if (bounds.west == -180 && bounds.east == 180) {
+      return null;
+    }
 
     return camera.withPosition(
       center: camera.unprojectAtZoom(newCenterPix, testZoom),