Measure distance in scene

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// Copyright 2026 Esri
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//   https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//

import 'package:arcgis_maps/arcgis_maps.dart';
import 'package:arcgis_maps_sdk_flutter_samples/common/common.dart';
import 'package:flutter/material.dart';

class MeasureDistanceInScene extends StatefulWidget {
  const MeasureDistanceInScene({super.key});

  @override
  State<MeasureDistanceInScene> createState() => _MeasureDistanceInSceneState();
}

class _MeasureDistanceInSceneState extends State<MeasureDistanceInScene>
    with SampleStateSupport {
  // Create a controller for the scene view.
  final _sceneViewController = ArcGISSceneView.createController();

  // Create the distance measurement analysis with initial locations in Brest, France.
  final _locationDistanceMeasurement = ExploratoryLocationDistanceMeasurement(
    startLocation: ArcGISPoint(
      x: -4.494677,
      y: 48.384472,
      z: 24.772694,
      spatialReference: .wgs84,
    ),
    endLocation: ArcGISPoint(
      x: -4.495646,
      y: 48.384377,
      z: 58.501115,
      spatialReference: .wgs84,
    ),
  );

  // A variable to track the current state of the measurement process.
  var _measurementState = MeasurementState.setStartLocation;

  // A flag for when the scene view is ready and controls can be used.
  var _ready = false;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: SafeArea(
        top: false,
        left: false,
        right: false,
        child: Stack(
          children: [
            Column(
              children: [
                Expanded(
                  child: Stack(
                    children: [
                      // Add a scene view to the widget tree and set a controller.
                      ArcGISSceneView(
                        controllerProvider: () => _sceneViewController,
                        onSceneViewReady: onSceneViewReady,
                      ),
                      // Add a detector to handle long-press gestures for changing the measurement.
                      GestureDetector(
                        onLongPressStart: onLongPressStart,
                        onLongPressMoveUpdate: onLongPressMoveUpdate,
                        onLongPressEnd: onLongPressEnd,
                      ),
                    ],
                  ),
                ),
                // Add a StreamBuilder to listen to changes in the measurement and display the distance values.
                StreamBuilder(
                  stream: _locationDistanceMeasurement.onMeasurementChanged,
                  builder: (context, snapshot) {
                    final measurement = snapshot.data;
                    if (measurement == null) {
                      return const SizedBox.shrink();
                    }

                    return Column(
                      children: [
                        // Display the formatted distance values.
                        Text('Direct: ${measurement.directDistance.formatted}'),
                        Text(
                          'Horizontal: ${measurement.horizontalDistance.formatted}',
                        ),
                        Text(
                          'Vertical: ${measurement.verticalDistance.formatted}',
                        ),
                        // Add a segmented button to switch between unit systems.
                        SegmentedButton(
                          segments: [
                            ...UnitSystem.values.map(
                              (unitSystem) => ButtonSegment(
                                value: unitSystem,
                                label: Text(unitSystem.name.capitalized),
                              ),
                            ),
                          ],
                          selected: {_locationDistanceMeasurement.unitSystem},
                          onSelectionChanged: (newSelection) {
                            setState(
                              () => _locationDistanceMeasurement.unitSystem =
                                  newSelection.first,
                            );
                          },
                        ),
                      ],
                    );
                  },
                ),
              ],
            ),
            // Display a banner with instructions at the top.
            SafeArea(
              left: false,
              right: false,
              child: IgnorePointer(
                child: Container(
                  padding: const EdgeInsets.all(10),
                  color: Colors.white.withValues(alpha: 0.7),
                  child: Row(
                    mainAxisAlignment: MainAxisAlignment.center,
                    children: [
                      Text(
                        _measurementState.instructions,
                        textAlign: TextAlign.center,
                        style: Theme.of(context).textTheme.labelMedium,
                      ),
                    ],
                  ),
                ),
              ),
            ),
            // Display a progress indicator and prevent interaction until state is ready.
            LoadingIndicator(visible: !_ready),
          ],
        ),
      ),
    );
  }

  Future<void> onSceneViewReady() async {
    // Create a scene with a topographic basemap style.
    final scene = ArcGISScene.withBasemapStyle(.arcGISTopographic);
    _sceneViewController.arcGISScene = scene;

    // Set the initial camera position to look at the distance measurement locations.
    final lookAtPoint = Envelope.fromPoints(
      _locationDistanceMeasurement.startLocation,
      _locationDistanceMeasurement.endLocation,
    ).center;
    final camera = Camera.withLookAtPoint(
      lookAtPoint: lookAtPoint,
      distance: 200,
      heading: 0,
      pitch: 45,
      roll: 0,
    );
    scene.initialViewpoint = Viewpoint.withPointScaleCamera(
      center: lookAtPoint,
      scale: 1,
      camera: camera,
    );

    // Add the world elevation source to the scene's surface.
    final elevationSource = ArcGISTiledElevationSource.withUri(
      Uri.parse(
        'https://elevation3d.arcgis.com/arcgis/rest/services/WorldElevation3D/Terrain3D/ImageServer',
      ),
    );
    scene.baseSurface.elevationSources.add(elevationSource);

    // Add a scene layer of 3D buildings in Brest, France.
    final buildingsLayer = ArcGISSceneLayer.withUri(
      Uri.parse(
        'https://tiles.arcgis.com/tiles/P3ePLMYs2RVChkJx/arcgis/rest/services/Buildings_Brest/SceneServer/layers/0',
      ),
    );
    scene.operationalLayers.add(buildingsLayer);

    // Create an AnalysisOverlay and add the measurement analysis to it.
    final analysisOverlay = AnalysisOverlay();
    analysisOverlay.analyses.add(_locationDistanceMeasurement);

    // Add the AnalysisOverlay to the view controller.
    _sceneViewController.analysisOverlays.add(analysisOverlay);

    // Set the ready state variable to true to enable the sample UI.
    setState(() => _ready = true);
  }

  Future<void> onLongPressStart(LongPressStartDetails details) async {
    // Convert the screen point to a map point and set it as the start and end locations of the measurement.
    final mapPoint = await _sceneViewController.screenToLocation(
      screen: details.localPosition,
    );
    _locationDistanceMeasurement.startLocation = mapPoint;
    _locationDistanceMeasurement.endLocation = mapPoint;

    // Update the measurement state to be setting the end location.
    setState(() => _measurementState = MeasurementState.setEndLocation);
  }

  Future<void> onLongPressMoveUpdate(LongPressMoveUpdateDetails details) async {
    // Convert the screen point to a map point and update the end location of the measurement.
    final mapPoint = await _sceneViewController.screenToLocation(
      screen: details.localPosition,
    );
    _locationDistanceMeasurement.endLocation = mapPoint;
  }

  void onLongPressEnd(LongPressEndDetails details) {
    // Return the measurement state back to setting the start location.
    setState(() => _measurementState = MeasurementState.setStartLocation);
  }
}

// An enum to track the state of the long-press-and-drag measurement sequence.
enum MeasurementState {
  setStartLocation(instructions: 'Tap and hold to set the start location.'),
  setEndLocation(instructions: 'While holding, drag to set the end location.');

  const MeasurementState({required this.instructions});

  final String instructions;
}

extension on Distance {
  // A helper method to format the distance value with its unit for display.
  String get formatted => '${value.toStringAsFixed(2)} ${unit.abbreviation}';
}

extension on String {
  // A helper method to capitalize the first letter of a string.
  String get capitalized =>
      isEmpty ? this : '${this[0].toUpperCase()}${substring(1)}';
}