main.dart

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

void main() {
  runApp(const MaterialApp(home: AnimationPage()));
}

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

  @override
  State<AnimationPage> createState() => _AnimationPageState();
}

class _AnimationPageState extends State<AnimationPage>
    with TickerProviderStateMixin {
  late final AnimationController _controllerX;
  late final AnimationController _controllerY;

  final _boxSize = 60.0;

  double _valueX = 20;
  double _valueY = 20;

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

    /// [AnimationController] for x axis
    _controllerX = AnimationController.unbounded(vsync: this)..addListener(() {
      setState(() {
        _valueX = _controllerX.value;
      });
    });

    /// [AnimationController] for y axis
    _controllerY = AnimationController.unbounded(vsync: this)..addListener(() {
      setState(() {
        _valueY = _controllerY.value;
      });
    });
  }

  void _startFriction(Offset initialPosition, Offset velocity) {
    // start animation for x axis
    _controllerX.animateWith(
      FrictionSimulation(0.5, initialPosition.dx, velocity.dx),
    );

    // start another animation for y axis
    _controllerY.animateWith(
      FrictionSimulation(0.5, initialPosition.dy, velocity.dy),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: GestureDetector(
        // grab and move the box
        onPanUpdate: (details) {
          setState(() {
            _valueX = details.globalPosition.dx - _boxSize / 2;
            _valueY = details.globalPosition.dy - _boxSize / 2;
          });
        },
        // slide the ball
        onPanEnd: (details) {
          _startFriction(
            Offset(_valueX, _valueY),
            details
                .velocity
                .pixelsPerSecond, // velocity exposed by GestureDetector
          );
        },
        child: Stack(
          children: [
            CustomPaint(size: Size.infinite, painter: _GridPainter()),
            Positioned(
              top: _valueY,
              left: _valueX,
              child: Container(
                width: _boxSize,
                height: _boxSize,
                color: Colors.blue,
              ),
            ),
          ],
        ),
      ),
    );
  }
}

/// background grid
class _GridPainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    final paint =
        Paint()
          ..color = Colors.grey.withOpacity(0.3)
          ..strokeWidth = 0.5;

    for (var i = 0.0; i < size.width; i += 10) {
      canvas.drawLine(Offset(i, 0), Offset(i, size.height), paint);
    }

    for (var i = 0.0; i < size.height; i += 10) {
      canvas.drawLine(Offset(0, i), Offset(size.width, i), paint);
    }
  }

  @override
  bool shouldRepaint(covariant CustomPainter oldDelegate) => false;
}