motion_core

Pub Version License: MIT Platform

A Flutter plugin that provides a simple, high-performance, and unified stream of fused device motion data from native platform APIs.

motion_core demo

Overview

While Flutter provides access to raw sensors (via plugins like sensors_plus), there is no out-of-the-box equivalent to iOS Core Motion or Android's Fused Sensor APIs. To get a device's true orientation (attitude), developers typically need to implement complex sensor fusion algorithms (like Madgwick or Mahony filters) in Dart or build a native bridge.

motion_core is that bridge. It does the native work for you, exposing a single, clean stream of calibrated motion data by leveraging the best available technology on each platform.

Features

  • ✅ Unified Stream: Get a single Stream<MotionData> that works seamlessly on both iOS and Android.
  • 🚀 Native Performance: Leverages iOS CoreMotion (CMDeviceMotion) and Android's TYPE_ROTATION_VECTOR for battery-efficient, low-latency, hardware-accelerated fusion.
  • 📦 Comprehensive Motion Data: Provides the complete motion state in one object:
    • Attitude: Device orientation as a Quaternion.
    • Gravity: A Vector3 representing the direction of gravity.
    • User Acceleration: A Vector3 of acceleration applied by the user, with gravity removed.
    • Heading Accuracy: The estimated accuracy of the compass heading (in radians) on Android.
  • 🛠️ Sensor Availability Check: A simple async utility (MotionCore.isAvailable()) to check if the device has the necessary hardware.

Getting Started

1. Add to pubspec.yaml

Add motion_core and vector_math to your project's dependencies.

dependencies:
  flutter:
    sdk: flutter
  motion_core: ^1.0.0 # Use the latest version from pub.dev
  vector_math: ^2.1.4

2. Install

Run the following command in your terminal:

flutter pub get

Platform Specific Setup

This plugin requires platform-specific configuration to access motion data.

iOS (Mandatory)

You must add a usage description to your ios/Runner/Info.plist file. Without this, your app will crash on recent iOS versions when trying to access motion data and will be rejected by the App Store.

Open ios/Runner/Info.plist and add the following:

<key>NSMotionUsageDescription</key>
<string>This app requires access to motion data to determine device orientation and movement.</string>

Warning Failure to add the NSMotionUsageDescription key will result in a runtime crash. This is not optional.

Android

No permissions are required.

Access to the standard motion sensors (accelerometer, gyroscope, etc.) on Android does not require any special permissions in your AndroidManifest.xml.

Usage

Here is a complete example demonstrating how to use the plugin.

Basic Example

import 'dart:async';
import 'dart:math' show pi;
import 'package:flutter/material.dart';
import 'package:motion_core/motion_core.dart';
import 'package:vector_math/vector_math_64.dart' as v;

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      home: MotionDemoScreen(),
      theme: ThemeData.dark(),
    );
  }
}

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

  @override
  State<MotionDemoScreen> createState() => _MotionDemoScreenState();
}

class _MotionDemoScreenState extends State<MotionDemoScreen> {
  MotionData? _motionData;
  StreamSubscription? _motionSubscription;
  bool _isAvailable = false;

  @override
  void initState() {
    super.initState();
    _checkAvailabilityAndStart();
  }

  Future<void> _checkAvailabilityAndStart() async {
    bool available = await MotionCore.isAvailable();
    if (!mounted) return;

    setState(() {
      _isAvailable = available;
    });

    if (_isAvailable) {
      _startListening();
    }
  }

  void _startListening() {
    _motionSubscription = MotionCore.motionStream.listen((MotionData data) {
      if (mounted) {
        setState(() {
          _motionData = data;
        });
      }
    });
  }

  @override
  void dispose() {
    _motionSubscription?.cancel();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Motion Core Demo')),
      body: Center(
        child: !_isAvailable
            ? const Text('Required motion sensors are not available.')
            : _motionData == null
                ? const CircularProgressIndicator()
                : Column(
                    mainAxisAlignment: MainAxisAlignment.center,
                    children: [
                      // 3D Box visualizer
                      Transform(
                        transform: Matrix4.identity()
                          ..setEntry(3, 2, 0.001) // perspective
                          ..multiply(v.Matrix4.fromQuaternion(_motionData!.attitude)),
                        alignment: FractionalOffset.center,
                        child: Container(
                          width: 150,
                          height: 150,
                          decoration: BoxDecoration(
                            color: Colors.blueAccent.withOpacity(0.8),
                            borderRadius: BorderRadius.circular(20),
                            border: Border.all(color: Colors.white, width: 2),
                          ),
                          child: const Center(child: Text('FRONT', style: TextStyle(fontWeight: FontWeight.bold))),
                        ),
                      ),
                      const SizedBox(height: 30),
                      // Data table
                      Text('Pitch: ${(_motionData!.pitch * 180 / pi).toStringAsFixed(1)}°'),
                      Text('Roll: ${(_motionData!.roll * 180 / pi).toStringAsFixed(1)}°'),
                      Text('Yaw: ${(_motionData!.yaw * 180 / pi).toStringAsFixed(1)}°'),
                    ],
                  ),
      ),
    );
  }
}

Managing the Stream

The motionStream is a broadcast stream. It is important to manage your subscription according to your widget's lifecycle.

// Pause updates when the widget is not visible
_motionSubscription?.pause();

// Resume updates when the widget is visible again
_motionSubscription?.resume();

// Stop listening completely to prevent memory leaks
_motionSubscription?.cancel();

API Details

The MotionData Object

The stream provides MotionData objects, which contain the following properties:

Property Type Description
attitude Quaternion The device's orientation in 3D space.
gravity Vector3 The gravity vector, indicating the direction of gravity relative to the device.
userAcceleration Vector3 The acceleration applied by the user, with the effect of gravity removed.
headingAccuracy double? Android only. The estimated accuracy of the heading in radians. null on iOS.
pitch double A convenience getter for the pitch angle (in radians) from the attitude.
roll double A convenience getter for the roll angle (in radians) from the attitude.
yaw double A convenience getter for the yaw angle (in radians) from the attitude.

License

This project is licensed under the MIT License - see the LICENSE file for details.

Libraries

motion_core