Flutter Physics Simulation in Animation with Example

Flutter provides a rich set of animation widgets and classes that allow you to create animations in your app. One type of animation that you may want to create is a physics simulation animation, which simulates real-world physics to create dynamic and engaging animations. In this blog post, we will explore how to create a physics simulation animation in Flutter using the AnimatedBuilder and AnimationController widgets.

Step 1: Adding Animation Dependencies

First, we need to add the necessary dependencies for animations. You can do this by adding the following lines of code to your pubspec.yaml file:

dependencies:
  flutter:
    sdk: flutter
  box2d_flame: ^0.3.2​

In this code, we have added the box2d_flame package that provides physics simulation capabilities for Flutter.

Step 2: Creating an Animated Physics Simulation

Next, we will create an animated physics simulation using the AnimatedBuilder and AnimationController widgets.

import 'dart:math';
import 'package:box2d_flame/box2d.dart' as box2d;
import 'package:flutter/material.dart';
class PhysicsSimulationAnimation extends StatefulWidget {
  @override
  _PhysicsSimulationAnimationState createState() =>
      _PhysicsSimulationAnimationState();
}
class _PhysicsSimulationAnimationState
    extends State<PhysicsSimulationAnimation>
    with SingleTickerProviderStateMixin {
  AnimationController _controller;
  box2d.World _world;
  @override
  void initState() {
    super.initState();
    _controller = AnimationController(
      vsync: this,
      duration: Duration(seconds: 2),
    )..repeat();
    _world = box2d.World(box2d.Vector2.zero(), true);
    box2d.PolygonShape shape = box2d.PolygonShape();
    shape.setAsBoxXY(0.5, 0.5);
    box2d.FixtureDef fixtureDef = box2d.FixtureDef();
    fixtureDef.shape = shape;
    fixtureDef.density = 1.0;
    box2d.BodyDef bodyDef = box2d.BodyDef();
    bodyDef.type = box2d.BodyType.DYNAMIC;
    bodyDef.position = box2d.Vector2(0.0, 0.0);
    box2d.Body body = _world.createBody(bodyDef);
    body.createFixtureFromFixtureDef(fixtureDef);
  }
  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }
  @override
  Widget build(BuildContext context) {
    return Container(
      child: AnimatedBuilder(
        animation: _controller,
        builder: (BuildContext context, Widget child) {
          _world.step(_controller.value, 8, 3);
          box2d.Vector2 position =
              (_world.getBodyList().first?.position ?? box2d.Vector2.zero());
          return CustomPaint(
            painter: BallPainter(position),
            size: Size(200, 200),
          );
        },
      ),
    );
  }
}
class BallPainter extends CustomPainter {
  final box2d.Vector2 position;
  BallPainter(this.position);
  @override
  void paint(Canvas canvas, Size size) {
    Paint paint = Paint()..color = Colors.blue;
    canvas.drawCircle(
        Offset(position.x * size.width, position.y * size.height),
        20.0,
        paint);
  }
  @override
  bool shouldRepaint(CustomPainter oldDelegate) {
    return true;
  }
}​

In this code, we have created a PhysicsSimulationAnimation widget that uses the AnimatedBuilder widget to build a custom paint widget that