[google_maps_flutter] Add Projection methods to google_maps (flutter#2108)

[google_maps_flutter] Add Projection methods to google_maps

This doesn't yet expose the full projection functionality but
addresses the most common use-cases to translate screen coordinates
to latlngs.

Issue: flutter/flutter#37959

Author: iskakaushik

packages/google_maps_flutter/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.5.21+4
+
+* Support projection methods to translate between screen and latlng coordinates.
+
 ## 0.5.21+3
 
 * Fix `myLocationButton` bug in `google_maps_flutter` iOS.

packages/google_maps_flutter/android/src/main/java/io/flutter/plugins/googlemaps/Convert.java

@@ -201,11 +201,23 @@ static Object latLngToJson(LatLng latLng) {
     return Arrays.asList(latLng.latitude, latLng.longitude);
   }
 
-  private static LatLng toLatLng(Object o) {
+  static LatLng toLatLng(Object o) {
     final List<?> data = toList(o);
     return new LatLng(toDouble(data.get(0)), toDouble(data.get(1)));
   }
 
+  static Point toPoint(Object o) {
+    Map<String, Integer> screenCoordinate = (Map<String, Integer>) o;
+    return new Point(screenCoordinate.get("x"), screenCoordinate.get("y"));
+  }
+
+  static Map<String, Integer> pointToJson(Point point) {
+    final Map<String, Integer> data = new HashMap<>(2);
+    data.put("x", point.x);
+    data.put("y", point.y);
+    return data;
+  }
+
   private static LatLngBounds toLatLngBounds(Object o) {
     if (o == null) {
       return null;

packages/google_maps_flutter/android/src/main/java/io/flutter/plugins/googlemaps/GoogleMapController.java

@@ -17,6 +17,7 @@
 import android.app.Application;
 import android.content.Context;
 import android.content.pm.PackageManager;
+import android.graphics.Point;
 import android.os.Bundle;
 import android.util.Log;
 import android.view.View;
@@ -226,6 +227,32 @@ public void onMethodCall(MethodCall call, MethodChannel.Result result) {
           }
           break;
         }
+      case "map#getScreenCoordinate":
+        {
+          if (googleMap != null) {
+            LatLng latLng = Convert.toLatLng(call.arguments);
+            Point screenLocation = googleMap.getProjection().toScreenLocation(latLng);
+            result.success(Convert.pointToJson(screenLocation));
+          } else {
+            result.error(
+                "GoogleMap uninitialized",
+                "getScreenCoordinate called prior to map initialization",
+                null);
+          }
+          break;
+        }
+      case "map#getLatLng":
+        {
+          if (googleMap != null) {
+            Point point = Convert.toPoint(call.arguments);
+            LatLng latLng = googleMap.getProjection().fromScreenLocation(point);
+            result.success(Convert.latLngToJson(latLng));
+          } else {
+            result.error(
+                "GoogleMap uninitialized", "getLatLng called prior to map initialization", null);
+          }
+          break;
+        }
       case "camera#move":
         {
           final CameraUpdate cameraUpdate =

packages/google_maps_flutter/example/test_driver/google_maps.dart

@@ -564,4 +564,78 @@ void main() {
     final GoogleMapController controller = await controllerCompleter.future;
     await controller.setMapStyle(null);
   });
+
+  test('testGetLatLng', () async {
+    final Key key = GlobalKey();
+    final Completer<GoogleMapController> controllerCompleter =
+        Completer<GoogleMapController>();
+
+    await pumpWidget(Directionality(
+      textDirection: TextDirection.ltr,
+      child: GoogleMap(
+        key: key,
+        initialCameraPosition: _kInitialCameraPosition,
+        onMapCreated: (GoogleMapController controller) {
+          controllerCompleter.complete(controller);
+        },
+      ),
+    ));
+
+    final GoogleMapController controller = await controllerCompleter.future;
+
+    // We suspected a bug in the iOS Google Maps SDK caused the camera is not properly positioned at
+    // initialization. https://github.com/flutter/flutter/issues/24806
+    // This temporary workaround fix is provided while the actual fix in the Google Maps SDK is
+    // still being investigated.
+    // TODO(cyanglaz): Remove this temporary fix once the Maps SDK issue is resolved.
+    // https://github.com/flutter/flutter/issues/27550
+    await Future<dynamic>.delayed(const Duration(seconds: 3));
+
+    final LatLngBounds visibleRegion = await controller.getVisibleRegion();
+    final LatLng topLeft =
+        await controller.getLatLng(const ScreenCoordinate(x: 0, y: 0));
+    final LatLng northWest = LatLng(
+      visibleRegion.northeast.latitude,
+      visibleRegion.southwest.longitude,
+    );
+
+    expect(topLeft, northWest);
+  });
+
+  test('testScreenCoordinate', () async {
+    final Key key = GlobalKey();
+    final Completer<GoogleMapController> controllerCompleter =
+        Completer<GoogleMapController>();
+
+    await pumpWidget(Directionality(
+      textDirection: TextDirection.ltr,
+      child: GoogleMap(
+        key: key,
+        initialCameraPosition: _kInitialCameraPosition,
+        onMapCreated: (GoogleMapController controller) {
+          controllerCompleter.complete(controller);
+        },
+      ),
+    ));
+
+    final GoogleMapController controller = await controllerCompleter.future;
+
+    // We suspected a bug in the iOS Google Maps SDK caused the camera is not properly positioned at
+    // initialization. https://github.com/flutter/flutter/issues/24806
+    // This temporary workaround fix is provided while the actual fix in the Google Maps SDK is
+    // still being investigated.
+    // TODO(cyanglaz): Remove this temporary fix once the Maps SDK issue is resolved.
+    // https://github.com/flutter/flutter/issues/27550
+    await Future<dynamic>.delayed(const Duration(seconds: 3));
+
+    final LatLngBounds visibleRegion = await controller.getVisibleRegion();
+    final LatLng northWest = LatLng(
+      visibleRegion.northeast.latitude,
+      visibleRegion.southwest.longitude,
+    );
+    final ScreenCoordinate topLeft =
+        await controller.getScreenCoordinate(northWest);
+
+    expect(topLeft, const ScreenCoordinate(x: 0, y: 0));
+  });
 }

packages/google_maps_flutter/ios/Classes/GoogleMapController.m

@@ -8,7 +8,9 @@
 #pragma mark - Conversion of JSON-like values sent via platform channels. Forward declarations.
 
 static NSDictionary* PositionToJson(GMSCameraPosition* position);
+static NSDictionary* PointToJson(CGPoint point);
 static NSArray* LocationToJson(CLLocationCoordinate2D position);
+static CGPoint ToCGPoint(NSDictionary* json);
 static GMSCameraPosition* ToOptionalCameraPosition(NSDictionary* json);
 static GMSCoordinateBounds* ToOptionalBounds(NSArray* json);
 static GMSCameraUpdate* ToCameraUpdate(NSArray* data);
@@ -147,6 +149,26 @@ - (void)onMethodCall:(FlutterMethodCall*)call result:(FlutterResult)result {
                                  message:@"getVisibleRegion called prior to map initialization"
                                  details:nil]);
     }
+  } else if ([call.method isEqualToString:@"map#getScreenCoordinate"]) {
+    if (_mapView != nil) {
+      CLLocationCoordinate2D location = [FLTGoogleMapJsonConversions toLocation:call.arguments];
+      CGPoint point = [_mapView.projection pointForCoordinate:location];
+      result(PointToJson(point));
+    } else {
+      result([FlutterError errorWithCode:@"GoogleMap uninitialized"
+                                 message:@"getScreenCoordinate called prior to map initialization"
+                                 details:nil]);
+    }
+  } else if ([call.method isEqualToString:@"map#getLatLng"]) {
+    if (_mapView != nil && call.arguments) {
+      CGPoint point = ToCGPoint(call.arguments);
+      CLLocationCoordinate2D latlng = [_mapView.projection coordinateForPoint:point];
+      result(LocationToJson(latlng));
+    } else {
+      result([FlutterError errorWithCode:@"GoogleMap uninitialized"
+                                 message:@"getLatLng called prior to map initialization"
+                                 details:nil]);
+    }
   } else if ([call.method isEqualToString:@"map#waitForMap"]) {
     result(nil);
   } else if ([call.method isEqualToString:@"markers#update"]) {
@@ -427,6 +449,13 @@ - (void)mapView:(GMSMapView*)mapView didLongPressAtCoordinate:(CLLocationCoordin
   };
 }
 
+static NSDictionary* PointToJson(CGPoint point) {
+  return @{
+    @"x" : @((int)point.x),
+    @"y" : @((int)point.y),
+  };
+}
+
 static NSDictionary* GMSCoordinateBoundsToJson(GMSCoordinateBounds* bounds) {
   if (!bounds) {
     return nil;
@@ -460,6 +489,12 @@ static CLLocationCoordinate2D ToLocation(NSArray* data) {
   return json ? ToCameraPosition(json) : nil;
 }
 
+static CGPoint ToCGPoint(NSDictionary* json) {
+  double x = ToDouble(json[@"x"]);
+  double y = ToDouble(json[@"y"]);
+  return CGPointMake(x, y);
+}
+
 static GMSCoordinateBounds* ToBounds(NSArray* data) {
   return [[GMSCoordinateBounds alloc] initWithCoordinate:ToLocation(data[0])
                                               coordinate:ToLocation(data[1])];

packages/google_maps_flutter/lib/google_maps_flutter.dart

@@ -17,17 +17,18 @@ part 'src/bitmap.dart';
 part 'src/callbacks.dart';
 part 'src/camera.dart';
 part 'src/cap.dart';
+part 'src/circle.dart';
+part 'src/circle_updates.dart';
 part 'src/controller.dart';
 part 'src/google_map.dart';
 part 'src/joint_type.dart';
+part 'src/location.dart';
 part 'src/marker.dart';
 part 'src/marker_updates.dart';
-part 'src/location.dart';
 part 'src/pattern_item.dart';
 part 'src/polygon.dart';
 part 'src/polygon_updates.dart';
 part 'src/polyline.dart';
 part 'src/polyline_updates.dart';
-part 'src/circle.dart';
-part 'src/circle_updates.dart';
+part 'src/screen_coordinate.dart';
 part 'src/ui.dart';

packages/google_maps_flutter/lib/src/controller.dart

@@ -208,4 +208,25 @@ class GoogleMapController {
 
     return LatLngBounds(northeast: northeast, southwest: southwest);
   }
+
+  /// Return [ScreenCoordinate] of the [LatLng] in the current map view.
+  ///
+  /// A projection is used to translate between on screen location and geographic coordinates.
+  /// Screen location is in screen pixels (not display pixels) with respect to the top left corner
+  /// of the map, not necessarily of the whole screen.
+  Future<ScreenCoordinate> getScreenCoordinate(LatLng latLng) async {
+    final Map<String, int> point = await channel.invokeMapMethod<String, int>(
+        'map#getScreenCoordinate', latLng._toJson());
+    return ScreenCoordinate(x: point['x'], y: point['y']);
+  }
+
+  /// Returns [LatLng] corresponding to the [ScreenCoordinate] in the current map view.
+  ///
+  /// Returned [LatLng] corresponds to a screen location. The screen location is specified in screen
+  /// pixels (not display pixels) relative to the top left of the map, not top left of the whole screen.
+  Future<LatLng> getLatLng(ScreenCoordinate screenCoordinate) async {
+    final List<dynamic> latLng = await channel.invokeMethod<List<dynamic>>(
+        'map#getLatLng', screenCoordinate._toJson());
+    return LatLng(latLng[0], latLng[1]);
+  }
 }

packages/google_maps_flutter/lib/src/screen_coordinate.dart

@@ -0,0 +1,39 @@
+// Copyright 2019 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+part of google_maps_flutter;
+
+/// Represents a point coordinate in the [GoogleMap]'s view.
+///
+/// The screen location is specified in screen pixels (not display pixels) relative
+/// to the top left of the map, not top left of the whole screen. (x, y) = (0, 0)
+/// corresponds to top-left of the [GoogleMap] not the whole screen.
+@immutable
+class ScreenCoordinate {
+  const ScreenCoordinate({
+    @required this.x,
+    @required this.y,
+  });
+
+  final int x;
+  final int y;
+
+  dynamic _toJson() {
+    return <String, int>{
+      "x": x,
+      "y": y,
+    };
+  }
+
+  @override
+  String toString() => '$runtimeType($x, $y)';
+
+  @override
+  bool operator ==(Object o) {
+    return o is ScreenCoordinate && o.x == x && o.y == y;
+  }
+
+  @override
+  int get hashCode => hashValues(x, y);
+}

packages/google_maps_flutter/pubspec.yaml

@@ -2,7 +2,7 @@ name: google_maps_flutter
 description: A Flutter plugin for integrating Google Maps in iOS and Android applications.
 author: Flutter Team <[email protected]>
 homepage: https://github.com/flutter/plugins/tree/master/packages/google_maps_flutter
-version: 0.5.21+3
+version: 0.5.21+4
 
 dependencies:
   flutter: