magnifying_class.dart

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

const Color darkBlue = Color.fromARGB(255, 18, 32, 47);

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

class MyApp extends StatefulWidget {
  @override
  State<MyApp> createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  var glassCenter = const Offset(150, 150);

  @override
  Widget build(BuildContext context) {
    const glassSize = Size(200, 200);
    const glassZoom = 1.25;
    final glassOffset = glassCenter - glassSize.center(Offset.zero);
    final centerCorrection = (glassCenter * (glassZoom - 1.0)) * -1.0;

    return MaterialApp(
      theme: ThemeData.dark().copyWith(
        scaffoldBackgroundColor: darkBlue,
      ),
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        body: MouseRegion(
          onHover: (details) {
            setState(() {
              glassCenter = details.localPosition;
            });
          },
          child: LayoutBuilder(builder: (context, constraints) {
            final imageFilterMatrix = Matrix4.translationValues(
                  centerCorrection.dx,
                  centerCorrection.dy,
                  0,
                ) *
                Matrix4.identity().scaled(glassZoom);

            final imageFilter = ImageFilter.matrix(imageFilterMatrix.storage);

            return Stack(children: [
              Center(
                child: Container(
                  width: 200,
                  height: 200,
                  decoration: const BoxDecoration(
                    shape: BoxShape.rectangle,
                    color: Colors.red,
                  ),
                ),
              ),
              Positioned(
                top: glassOffset.dy,
                left: glassOffset.dx,
                width: glassSize.width,
                height: glassSize.height,
                child: ClipOval(
                  child: BackdropFilter(
                    filter: imageFilter,
                    child: const ColoredBox(
                      color: Colors.transparent,
                    ),
                  ),
                ),
              )
            ]);
          }),
        ),
      ),
    );
  }
}