Flutter physics animation

main.dart

import 'package:flutter/material.dart';
import 'package:flutter/physics.dart';

class DraggableSquare extends StatefulWidget {
  const DraggableSquare({super.key});
  @override
  State<DraggableSquare> createState() => _DraggableSquareState();
}

class _DraggableSquareState extends State<DraggableSquare> with SingleTickerProviderStateMixin {
  var originalPostion = const Offset(150.0, 150.0);
  late double _left;
  late double _top;
  late AnimationController _controller;
  late Animation<Offset> _animation;

  @override
  void initState() {
    super.initState();
    _left = originalPostion.dx;
    _top = originalPostion.dy;
    _controller = AnimationController.unbounded(vsync: this)
      ..addListener(() {
        setState(() {
          _left = _animation.value.dx;
          _top = _animation.value.dy;
        });
      });
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  void _runAnimation() {
    _animation = _controller.drive(Tween<Offset>(
      begin: Offset(_left, _top),
      end: originalPostion,
    ));

    const spring = SpringDescription(
      mass: 1.0,
      stiffness: 100.0,
      damping: 10.0,
    );
    final simulation = SpringSimulation(spring, 0.0, 1.0, 0);
    _controller.animateWith(simulation);
  }

  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onPanDown: (details) {
        _controller.stop();
      },
      onPanUpdate: (details) {
        setState(() {
          _left += details.delta.dx;
          _top += details.delta.dy;
        });
      },
      onPanEnd: (details) {
        _runAnimation();
      },
      child: Stack(
        children: [
          Positioned(
            left: _left,
            top: _top,
            child: Container(
              width: 100.0,
              height: 100.0,
              color: Colors.blue,
            ),
          ),
        ],
      ),
    );
  }
}

void main() {
  runApp(const MaterialApp(
    home: Scaffold(
      body: DraggableSquare(),
    ),
  ));
}