AppFlowy/frontend/app_flowy/lib/core/frameless_window.dart

import 'package:flutter/services.dart';
import 'package:flutter/material.dart';
import 'dart:io' show Platform;

class CocoaWindowChannel {
  CocoaWindowChannel._();

  final MethodChannel _channel = const MethodChannel("flutter/cocoaWindow");

  static final CocoaWindowChannel instance = CocoaWindowChannel._();

  Future<void> setWindowPosition(Offset offset) async {
    await _channel.invokeMethod("setWindowPosition", [offset.dx, offset.dy]);
  }

  Future<List<double>> getWindowPosition() async {
    final raw = await _channel.invokeMethod("getWindowPosition");
    final arr = raw as List<dynamic>;
    final List<double> result = arr.map((s) => s as double).toList();
    return result;
  }

  Future<void> zoom() async {
    await _channel.invokeMethod("zoom");
  }
}

class MoveWindowDetector extends StatefulWidget {
  const MoveWindowDetector({Key? key, this.child}) : super(key: key);

  final Widget? child;

  @override
  _MoveWindowDetectorState createState() => _MoveWindowDetectorState();
}

class _MoveWindowDetectorState extends State<MoveWindowDetector> {
  double winX = 0;
  double winY = 0;

  @override
  Widget build(BuildContext context) {
    if (!Platform.isMacOS) {
      return widget.child ?? Container();
    }
    return GestureDetector(
      // https://stackoverflow.com/questions/52965799/flutter-gesturedetector-not-working-with-containers-in-stack
      behavior: HitTestBehavior.translucent,
      onDoubleTap: () async {
        await CocoaWindowChannel.instance.zoom();
      },
      onPanStart: (DragStartDetails details) {
        winX = details.globalPosition.dx;
        winY = details.globalPosition.dy;
      },
      onPanUpdate: (DragUpdateDetails details) async {
        final windowPos = await CocoaWindowChannel.instance.getWindowPosition();
        final double dx = windowPos[0];
        final double dy = windowPos[1];
        final deltaX = details.globalPosition.dx - winX;
        final deltaY = details.globalPosition.dy - winY;
        await CocoaWindowChannel.instance.setWindowPosition(Offset(dx + deltaX, dy - deltaY));
      },
      child: widget.child,
    );
  }
}