How to make opaque tutorial screen in flutter?

As RoyalGriffin mentioned, you can use highlighter_coachmark library, and I am also aware of the error you are getting, the error is there because you are using RangeSlider class which is imported from 2 different packages. Can you try this example in your app and check if it is working?

1. Add highlighter_coachmark to your pubspec.yaml file

   dependencies:  flutter:    sdk: flutter  highlighter_coachmark: ^0.0.3

2. Run flutter packages get

Example:

import 'package:highlighter_coachmark/highlighter_coachmark.dart';void main() => runApp(MaterialApp(home: HomePage()));class HomePage extends StatefulWidget {  @override  State<HomePage> createState() => _HomePageState();}class _HomePageState extends State<HomePage> {  GlobalKey _fabKey = GlobalObjectKey("fab"); // used by FAB  GlobalKey _buttonKey = GlobalObjectKey("button"); // used by RaisedButton  @override  Widget build(BuildContext context) {    return Scaffold(      floatingActionButton: FloatingActionButton(        key: _fabKey, // setting key        onPressed: null,        child: Icon(Icons.add),      ),      body: Center(        child: RaisedButton(          key: _buttonKey, // setting key          onPressed: showFAB,          child: Text("RaisedButton"),        ),      ),    );  }  // we trigger this method on RaisedButton click  void showFAB() {    CoachMark coachMarkFAB = CoachMark();    RenderBox target = _fabKey.currentContext.findRenderObject();    // you can change the shape of the mark    Rect markRect = target.localToGlobal(Offset.zero) & target.size;    markRect = Rect.fromCircle(center: markRect.center, radius: markRect.longestSide * 0.6);    coachMarkFAB.show(      targetContext: _fabKey.currentContext,      markRect: markRect,      children: [        Center(          child: Text(            "This is called\nFloatingActionButton",            style: const TextStyle(              fontSize: 24.0,              fontStyle: FontStyle.italic,              color: Colors.white,            ),          ),        )      ],      duration: null, // we don't want to dismiss this mark automatically so we are passing null      // when this mark is closed, after 1s we show mark on RaisedButton      onClose: () => Timer(Duration(seconds: 1), () => showButton()),    );  }  // this is triggered once first mark is dismissed  void showButton() {    CoachMark coachMarkTile = CoachMark();    RenderBox target = _buttonKey.currentContext.findRenderObject();    Rect markRect = target.localToGlobal(Offset.zero) & target.size;    markRect = markRect.inflate(5.0);    coachMarkTile.show(      targetContext: _fabKey.currentContext,      markRect: markRect,      markShape: BoxShape.rectangle,      children: [        Positioned(          top: markRect.bottom + 15.0,          right: 5.0,          child: Text(            "And this is a RaisedButton",            style: const TextStyle(              fontSize: 24.0,              fontStyle: FontStyle.italic,              color: Colors.white,            ),          ),        )      ],      duration: Duration(seconds: 5), // this effect will only last for 5s    );  }}

Output:

You can use this library to help you achieve what you need. It allows you to mark views which you want to highlight and how you want to highlight them.

Wrap your current top widget with a Stack widget, having the first child of the Stack your current widget.Below this widget add a Container with black color, wrapped with Opacity like so:

return Stack(  children: <Widget>[    Scaffold( //first child of the stack - the current widget you have        body: Center(          child: Column(            mainAxisAlignment: MainAxisAlignment.spaceAround,            children: <Widget>[              Text("Foo"),              Text("Bar"),            ],          ),        )),    Opacity( //seconds child - Opaque layer      opacity: 0.7,      child: Container(        decoration: BoxDecoration(color: Colors.black),      ),    )  ],);

you then need to create image assets of the descriptions and arrows, in 1x, 2x, 3x resolutions, and place them in your assets folder in the appropriate structure as described here: https://flutter.dev/docs/development/ui/assets-and-images#declaring-resolution-aware-image-assets

you can then use Image.asset(...) widget to load your images (they will be loaded in the correct resolution), and place these widgets on a different container that will also be a child of the stack, and will be placed below the black container in the children list (the Opacity widget on the example above).