StickerWidget (panning only)

main.dart

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: StickerWidget(),
      ),
    );
  }
}

class StickerWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Stack(
      children: [
        Source(),
        Sticker('1', 0, 0, 100, 100),
        Sticker('2', 200, 200, 100, 200),
      ],
    );
  }
}

class Source extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return SizedBox.expand(
      child: Container(
        color: Colors.blue,
        child: Center(child: Text('source')),
      ),
    );
  }
}

class Sticker extends StatefulWidget {
  final String text;
  final double left;
  final double top;
  final double width;
  final double height;

  Sticker(
    this.text,
    this.left,
    this.top,
    this.width,
    this.height,
  );

  @override
  State<Sticker> createState() => _StickerState();
}

class _StickerState extends State<Sticker> {
  ValueNotifier<Rect> rect;

  initState() {
    super.initState();
    rect = ValueNotifier(Rect.fromLTWH(
      widget.left,
      widget.top,
      widget.width,
      widget.height,
    ));
  }

  @override
  Widget build(BuildContext context) {
    return AnimatedBuilder(
      animation: rect,
      builder: (_, child) => Stack(
        children: [
          Positioned.fromRect(
            child: GestureDetector(
              child: child,
              onPanUpdate: (details) {
                final r = rect.value;
                final offset = r.topLeft;
                final delta = details.delta;
                rect.value = Rect.fromLTWH(
                  offset.dx + delta.dx,
                  offset.dy + delta.dy,
                  r.width,
                  r.height,
                );
              },
            ),
            rect: rect.value,
          ),
          Positioned(
            child: Icon(Icons.close),
            left: rect.value.left,
            top: rect.value.top,
          ),
        ],
      ),
      child: SizedBox.expand(
        child: Container(
          child: Center(
            child: Text(widget.text),
          ),
          color: Colors.red,
        ),
      ),
    );
  }
}