Tooltip size test - For testing legibility of different sizes on different platforms

main.dart

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

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

class _MyAppState extends State<MyApp> {
  bool isDarkMode;

  @override
  void initState() {
    isDarkMode = false;
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Tooltip Size Test',
      debugShowCheckedModeBanner: false,
      theme: ThemeData.from(colorScheme: ColorScheme.light()),
      darkTheme: ThemeData.from(colorScheme: ColorScheme.dark()),
      themeMode: isDarkMode ? ThemeMode.dark : ThemeMode.light,
      home: TooltipTest(
        setDarkMode: (bool value) {
          setState(() {
            isDarkMode = value;
          });
        },
      ),
    );
  }
}

class TooltipTest extends StatefulWidget {
  const TooltipTest({
    Key key,
    this.setDarkMode,
  }) : super(key: key);
  final ValueChanged<bool> setDarkMode;

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

class _TooltipTestState extends State<TooltipTest> {
  bool isDarkMode;

  @override
  void initState() {
    isDarkMode = false;
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Tooltips Sample'),
        elevation: 0,
      ),
      body: SingleChildScrollView(
        child: Padding(
          padding: const EdgeInsets.symmetric(horizontal: 12),
          child: Column(
            children: [
              Text('Tooltips on Windows Desktop',
                  style: Theme.of(context).textTheme.headline5),
              Text(
                  'Device pixel ratio is ${MediaQuery.of(context).devicePixelRatio}'),
              SwitchListTile.adaptive(
                title: const Text(
                  'Change theme mode',
                ),
                value: isDarkMode,
                onChanged: (bool value) {
                  setState(() {
                    isDarkMode = value;
                    widget.setDarkMode(isDarkMode);
                  });
                },
              ),
              const SizedBox(height: 10),
              Row(
                mainAxisAlignment: MainAxisAlignment.spaceBetween,
                children: [
                  FakeTooltip(
                    message: 'Tooltip message ijklmnop ABC 123',
                    fontSize: 9,
                  ),
                  Text('Default system font, size 9'),
                ],
              ),
              const SizedBox(height: 10),
              Row(
                mainAxisAlignment: MainAxisAlignment.spaceBetween,
                children: [
                  FakeTooltip(
                    message: 'Tooltip message ijklmnop ABC 123',
                    fontSize: 10,
                  ),
                  Text('Default system font, size 10'),
                ],
              ),
              const SizedBox(height: 10),
              Row(
                mainAxisAlignment: MainAxisAlignment.spaceBetween,
                children: [
                  FakeTooltip(
                    message: 'Tooltip message ijklmnop ABC 123',
                    fontSize: 11,
                  ),
                  Text('Default system font, size 11'),
                ],
              ),
              const SizedBox(height: 10),
              Row(
                mainAxisAlignment: MainAxisAlignment.spaceBetween,
                children: [
                  FakeTooltip(
                    message: 'Tooltip message ijklmnop ABC 123',
                    fontSize: 12,
                  ),
                  Text('Default system font, size 12'),
                ],
              ),
              const SizedBox(height: 10),
              Row(
                mainAxisAlignment: MainAxisAlignment.spaceBetween,
                children: [
                  FakeTooltip(
                    message: 'Tooltip message ijklmnop ABC 123',
                    fontSize: 13,
                  ),
                  Text('Default system font, size 13'),
                ],
              ),
              const SizedBox(height: 10),
              Row(
                mainAxisAlignment: MainAxisAlignment.spaceBetween,
                children: [
                  FakeTooltip(
                    message: 'Tooltip message ijklmnop ABC 123',
                    fontSize: 14,
                  ),
                  Text('Default system font, size 14'),
                ],
              )
            ],
          ),
        ),
      ),
    );
  }
}

class FakeTooltip extends StatelessWidget {
  const FakeTooltip({
    Key key,
    this.message,
    this.height = 24,
    this.fontSize = 10,
    this.padding = const EdgeInsets.symmetric(horizontal: 8.0),
    this.margin = const EdgeInsets.all(0.0),
  }) : super(key: key);

  final String message;
  final double height;
  final double fontSize;
  final EdgeInsetsGeometry padding;
  final EdgeInsetsGeometry margin;

  @override
  Widget build(BuildContext context) {
    final ThemeData theme = Theme.of(context);
    BoxDecoration decoration;
    TextStyle textStyle;

    if (theme.brightness == Brightness.dark) {
      textStyle = theme.textTheme.bodyText2.copyWith(
        color: Colors.black,
        fontSize: fontSize,
      );
      decoration = BoxDecoration(
        color: Colors.white.withOpacity(0.9),
        borderRadius: const BorderRadius.all(Radius.circular(4)),
      );
    } else {
      textStyle = theme.textTheme.bodyText2.copyWith(
        color: Colors.white,
        fontSize: fontSize,
      );
      decoration = BoxDecoration(
        color: Colors.grey[700].withOpacity(0.9),
        borderRadius: const BorderRadius.all(Radius.circular(4)),
      );
    }

    return ConstrainedBox(
      constraints: BoxConstraints(minHeight: height),
      child: DefaultTextStyle(
        style: Theme.of(context).textTheme.bodyText2,
        child: Container(
          decoration: decoration,
          padding: padding,
          margin: margin,
          child: Center(
            widthFactor: 1.0,
            heightFactor: 1.0,
            child: Text(
              message,
              style: textStyle,
            ),
          ),
        ),
      ),
    );
  }
}

Related to Flutter issue flutter/flutter#71052