Add parameter to fit to integer zoom levels

lib/flutter_map.dart

@@ -336,11 +336,17 @@ class FitBoundsOptions {
   final double? zoom;
   final bool inside;
 
+  /// By default calculations will return fractional zoom levels.
+  /// If this parameter is set to [true] fractional zoom levels will be round
+  /// to the next suitable integer.
+  final bool forceIntegerZoomLevel;
+
   const FitBoundsOptions({
     this.padding = EdgeInsets.zero,
     this.maxZoom = 17.0,
     this.zoom,
     this.inside = false,
+    this.forceIntegerZoomLevel = false,
   });
 }
 

lib/src/map/flutter_map_state.dart

@@ -514,7 +514,12 @@ class FlutterMapState extends MapGestureMixin
 
     final paddingTotalXY = paddingTL + paddingBR;
 
-    var zoom = getBoundsZoom(bounds, paddingTotalXY, inside: options.inside);
+    var zoom = getBoundsZoom(
+      bounds,
+      paddingTotalXY,
+      inside: options.inside,
+      forceIntegerZoomLevel: options.forceIntegerZoomLevel,
+    );
     zoom = math.min(options.maxZoom, zoom);
 
     final paddingOffset = (paddingBR - paddingTL) / 2;
@@ -528,7 +533,7 @@ class FlutterMapState extends MapGestureMixin
   }
 
   double getBoundsZoom(LatLngBounds bounds, CustomPoint<double> padding,
-      {bool inside = false}) {
+      {bool inside = false, bool forceIntegerZoomLevel = false}) {
     var zoom = this.zoom;
     final min = options.minZoom ?? 0.0;
     final max = options.maxZoom ?? double.infinity;
@@ -544,6 +549,10 @@ class FlutterMapState extends MapGestureMixin
 
     zoom = getScaleZoom(scale, zoom);
 
+    if (forceIntegerZoomLevel) {
+      zoom = inside ? zoom.ceilToDouble() : zoom.floorToDouble();
+    }
+
     return math.max(min, math.min(max, zoom));
   }
 

test/flutter_map_controller_test.dart

@@ -0,0 +1,145 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_map/flutter_map.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:latlong2/latlong.dart';
+
+void main() {
+  testWidgets('test fit bounds methods', (tester) async {
+    final controller = MapController();
+    final bounds = LatLngBounds(
+      LatLng(51, 0),
+      LatLng(52, 1),
+    );
+    final expectedCenter = LatLng(51.50274289405741, 0.49999999999999833);
+
+    await tester.pumpWidget(TestApp(controller: controller));
+
+    {
+      const fitOptions = FitBoundsOptions();
+
+      final expectedBounds = LatLngBounds(
+        LatLng(51.00145915187144, -0.3079873797085076),
+        LatLng(52.001427481787005, 1.298485398623206),
+      );
+      const expectedZoom = 7.451812751543818;
+
+      final fit = controller.centerZoomFitBounds(bounds, options: fitOptions);
+      controller.move(fit.center, fit.zoom);
+      await tester.pump();
+      expect(controller.bounds, equals(expectedBounds));
+      expect(controller.center, equals(expectedCenter));
+      expect(controller.zoom, equals(expectedZoom));
+
+      controller.fitBounds(bounds, options: fitOptions);
+      await tester.pump();
+      expect(controller.bounds, equals(expectedBounds));
+      expect(controller.center, equals(expectedCenter));
+      expect(controller.zoom, equals(expectedZoom));
+    }
+
+    {
+      const fitOptions = FitBoundsOptions(
+        forceIntegerZoomLevel: true,
+      );
+
+      final expectedBounds = LatLngBounds(
+        LatLng(50.819818262156545, -0.6042480468750001),
+        LatLng(52.1874047455997, 1.5930175781250002),
+      );
+      const expectedZoom = 7;
+
+      final fit = controller.centerZoomFitBounds(bounds, options: fitOptions);
+      controller.move(fit.center, fit.zoom);
+      await tester.pump();
+      expect(controller.bounds, equals(expectedBounds));
+      expect(controller.center, equals(expectedCenter));
+      expect(controller.zoom, equals(expectedZoom));
+
+      controller.fitBounds(bounds, options: fitOptions);
+      await tester.pump();
+      expect(controller.bounds, equals(expectedBounds));
+      expect(controller.center, equals(expectedCenter));
+      expect(controller.zoom, equals(expectedZoom));
+    }
+
+    {
+      const fitOptions = FitBoundsOptions(
+        inside: true,
+      );
+
+      final expectedBounds = LatLngBounds(
+        LatLng(51.19148727133182, -6.195044477408375e-13),
+        LatLng(51.8139520195805, 0.999999999999397),
+      );
+      const expectedZoom = 8.135709286104404;
+
+      final fit = controller.centerZoomFitBounds(bounds, options: fitOptions);
+      controller.move(fit.center, fit.zoom);
+      await tester.pump();
+
+      expect(controller.bounds, equals(expectedBounds));
+      expect(controller.center, equals(expectedCenter));
+      expect(controller.zoom, equals(expectedZoom));
+
+      controller.fitBounds(bounds, options: fitOptions);
+      await tester.pump();
+      expect(controller.bounds, equals(expectedBounds));
+      expect(controller.center, equals(expectedCenter));
+      expect(controller.zoom, equals(expectedZoom));
+    }
+
+    {
+      const fitOptions = FitBoundsOptions(
+        inside: true,
+        forceIntegerZoomLevel: true,
+      );
+
+      final expectedBounds = LatLngBounds(
+        LatLng(51.33232774035881, 0.22521972656250003),
+        LatLng(51.67425842259517, 0.7745361328125),
+      );
+      const expectedZoom = 9;
+
+      final fit = controller.centerZoomFitBounds(bounds, options: fitOptions);
+      controller.move(fit.center, fit.zoom);
+      await tester.pump();
+      expect(controller.bounds, equals(expectedBounds));
+      expect(controller.center, equals(expectedCenter));
+      expect(controller.zoom, equals(expectedZoom));
+
+      controller.fitBounds(bounds, options: fitOptions);
+      await tester.pump();
+      expect(controller.bounds, equals(expectedBounds));
+      expect(controller.center, equals(expectedCenter));
+      expect(controller.zoom, equals(expectedZoom));
+    }
+  });
+}
+
+class TestApp extends StatelessWidget {
+  final MapController controller;
+
+  const TestApp({
+    required this.controller,
+    Key? key,
+  }) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      home: Scaffold(
+        body: Center(
+          // ensure that map is always of the same size
+          child: SizedBox(
+            width: 200,
+            height: 200,
+            child: FlutterMap(
+              mapController: controller,
+              options: MapOptions(),
+            ),
+          ),
+        ),
+      ),
+    );
+  }
+}