flutter/examples/api/lib/widgets/transitions/relative_positioned_transition.0.dart

// Copyright 2014 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'package:flutter/material.dart';

/// Flutter code sample for [RelativePositionedTransition].

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

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

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      home: RelativePositionedTransitionExample(),
    );
  }
}

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

  @override
  State<RelativePositionedTransitionExample> createState() => _RelativePositionedTransitionExampleState();
}

/// [AnimationController]s can be created with `vsync: this` because of
/// [TickerProviderStateMixin].
class _RelativePositionedTransitionExampleState extends State<RelativePositionedTransitionExample>
    with TickerProviderStateMixin {
  late final AnimationController _controller = AnimationController(
    duration: const Duration(seconds: 2),
    vsync: this,
  )..repeat(reverse: true);

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

  @override
  Widget build(BuildContext context) {
    const double smallLogo = 100;
    const double bigLogo = 200;

    return LayoutBuilder(
      builder: (BuildContext context, BoxConstraints constraints) {
        final Size biggest = constraints.biggest;
        return Stack(
          children: <Widget>[
            RelativePositionedTransition(
              size: biggest,
              rect: RectTween(
                begin: const Rect.fromLTWH(0, 0, bigLogo, bigLogo),
                end: Rect.fromLTWH(
                  biggest.width - smallLogo,
                  biggest.height - smallLogo,
                  smallLogo,
                  smallLogo,
                ),
              ).animate(CurvedAnimation(
                parent: _controller,
                curve: Curves.elasticInOut,
              )),
              child: const Padding(
                padding: EdgeInsets.all(8),
                child: FlutterLogo(),
              ),
            ),
          ],
        );
      },
    );
  }
}