How can I initiate drawing on my Google Map? - flutter

Question

I found this library: https://pub.dev/packages/flutter_map_picker
I looked through his code and tried figuring out how he initiates drawing. What he accomplishes is far more complicated than I need, and I can't figure out the first step of what he did. I also don't want to take the guy's code. Can anyone explain how to accomplish this?
I just want to be able to circle objects on my map. There seems to be a polyline solution but it's just straight lines from a list of coordinates, not exactly what I'm looking for.

Answer 1

A Stack widget with GoogleMap and CustomPaint will let you draw anything you want on top of the map.
Stack(
children: <Widget>[
_position == null
? Text('Waiting for location . .')
: GoogleMap(
liteModeEnabled: false,
compassEnabled: true,
mapType: MapType.hybrid,
markers: Set<Marker>.of(markers.values),
initialCameraPosition: CameraPosition(
target: LatLng(_position.latitude, _position.longitude),
zoom: 17,
tilt: 0,
),
onMapCreated: (GoogleMapController controller) {
_mapController = controller;
// trigger initial update and paint of landmarks
_updateLandmarks();
},
onCameraMove: (CameraPosition position) {
_updateLandmarks();
},
),
CustomPaint(
foregroundPainter: MapPainter(_landmarksMap),
),
],
)
You have to convert map coordinates to device screen coordinates. Google has a cookbook on how to do that except it does not work in Flutter since the map plugin does not expose the complete API. But there is a way to do it of course.
void _updateLandmarks() async {
double dpi = MediaQuery.of(context).devicePixelRatio;
LatLngBounds bounds = await _mapController.getVisibleRegion();
ScreenCoordinate topRight = await _mapController.getScreenCoordinate(bounds.northeast);
ScreenCoordinate bottomLeft = await _mapController.getScreenCoordinate(bounds.southwest);
_landmarksMap.values.forEach((element) async {
ScreenCoordinate sc = await _mapController.getScreenCoordinate(LatLng(element.pos.latitude, element.pos.longitude));
element.screenPoint.x = ((sc.x - bottomLeft.x) / dpi).floor();
element.screenPoint.y = ((sc.y - topRight.y) / dpi).floor();
});
setState(() {});
}
You can read here for more details: https://aperico.com/google-maps-with-custom-paint-in-flutter/