From e68dab42353ba27f24ac478a01bc51f3f2f14727 Mon Sep 17 00:00:00 2001
From: Vincent <vincent.langstrom@gmail.com>
Date: Thu, 26 Jul 2018 17:28:57 +0300
Subject: [PATCH] Add double-tap to zoom

Added the necessary code to support double-tap to zoom. Also added a dispose function.
---
 flutter_map/lib/src/gestures/gestures.dart    | 48 ++++++++++++++++++-
 .../lib/src/map/flutter_map_state.dart        |  1 +
 2 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/flutter_map/lib/src/gestures/gestures.dart b/flutter_map/lib/src/gestures/gestures.dart
index e83444308..1179af594 100644
--- a/flutter_map/lib/src/gestures/gestures.dart
+++ b/flutter_map/lib/src/gestures/gestures.dart
@@ -8,7 +8,7 @@ import 'package:latlong/latlong.dart';
 import 'package:flutter_map/flutter_map.dart';
 
 abstract class MapGestureMixin extends State<FlutterMap>
-    with SingleTickerProviderStateMixin {
+    with TickerProviderStateMixin {
   static const double _kMinFlingVelocity = 800.0;
 
   LatLng _mapCenterStart;
@@ -19,15 +19,22 @@ abstract class MapGestureMixin extends State<FlutterMap>
   Animation<Offset> _flingAnimation;
   Offset _animationOffset = Offset.zero;
 
+  AnimationController _doubleTapController;
+  Animation _doubleTapAnimation;
+
   FlutterMap get widget;
   MapState get mapState;
   MapState get map => mapState;
   MapOptions get options;
 
+  @override
   void initState() {
     super.initState();
     _controller = new AnimationController(vsync: this)
       ..addListener(_handleFlingAnimation);
+    _doubleTapController = new AnimationController(
+        vsync: this, duration: Duration(milliseconds: 200))
+      ..addListener(_handleDoubleTapZoomAnimation);
   }
 
   void handleScaleStart(ScaleStartDetails details) {
@@ -111,6 +118,38 @@ abstract class MapGestureMixin extends State<FlutterMap>
     options.onTap(latlng);
   }
 
+  void handleDoubleTap() {
+    ///Currently zooms in the center of the screen
+    ///TODO: change the newCenter to be where the user tapped, see https://github.com/flutter/flutter/issues/10048
+
+    _mapZoomStart = map.zoom;
+    _mapCenterStart = map.center;
+
+    double dScale = 2.0;
+    for (var i = 0; i < 2; i++) {
+      dScale = math.sqrt(dScale);
+    }
+
+    double newZoom = _mapZoomStart * dScale;
+
+    _doubleTapAnimation = new Tween<double>(
+      begin: _mapZoomStart,
+      end: newZoom,
+    )
+        .chain(new CurveTween(curve: Curves.fastOutSlowIn))
+        .animate(_doubleTapController);
+    _doubleTapController
+      ..value = 0.0
+      ..forward();
+  }
+
+  void _handleDoubleTapZoomAnimation() {
+    var newCenter = map.project(_mapCenterStart);
+    setState(() {
+      map.move(map.unproject(newCenter), _doubleTapAnimation.value);
+    });
+  }
+
   void _handleFlingAnimation() {
     setState(() {
       _animationOffset = _flingAnimation.value;
@@ -128,4 +167,11 @@ abstract class MapGestureMixin extends State<FlutterMap>
   Offset _pointToOffset(Point point) {
     return new Offset(point.x.toDouble(), point.y.toDouble());
   }
+
+  @override
+  void dispose() {
+    _controller.dispose();
+    _doubleTapController.dispose();
+    super.dispose();
+  }
 }
diff --git a/flutter_map/lib/src/map/flutter_map_state.dart b/flutter_map/lib/src/map/flutter_map_state.dart
index 6ffc660d2..b00b34c9f 100644
--- a/flutter_map/lib/src/map/flutter_map_state.dart
+++ b/flutter_map/lib/src/map/flutter_map_state.dart
@@ -30,6 +30,7 @@ class FlutterMapState extends MapGestureMixin {
         onScaleUpdate: handleScaleUpdate,
         onScaleEnd: handleScaleEnd,
         onTapUp: handleTapUp,
+        onDoubleTap: handleDoubleTap,
         child: new Container(
           child: new Stack(
             children: layerWidgets,