Meteograph

Open-source Android weather widget that puts a detailed forecast directly on your home screen — no ads, no tracking, no account. Choose a 48-hour or 7-day meteogram with temperature, precipitation, and daylight on a single glanceable chart. Powered by the free Open-Meteo API.

Features

• Two home-screen widgets: 48-hour chart (46h forecast + 6h past) and 7-day chart, both rendered natively via AndroidSVG
• Meteogram chart with:
  • Temperature line with gradient fill
  • Precipitation bars
  • Daylight intensity (computed from cloud cover and sun position)
  • Current time marker
  • Weekday labels (weekly) / hour labels (48h)
• Smart refresh:
  • Foreground timer checks every minute for stale data (>15 min) and redraws at half-hour boundaries
  • AlarmManager (~15 min inexact) catches up on device wake
  • WorkManager periodic task (~30 min) with network-connected constraint
  • BOOT_COMPLETED refresh on device restart
  • Event-driven updates (screen unlock, network change, locale/timezone change)
• Flexible location:
  • GPS with reverse geocoding (native platform geocoder)
  • City search via Open-Meteo geocoding API
  • Recent cities remembered
  • Berlin default when GPS unavailable
• Material You dynamic color support (Android 12+)
• Light/dark theme following system preference
• 36 languages supported
• Locale-aware units (°F for US/Liberia/Myanmar, °C elsewhere; 12/24h time)
• Offline support with smart caching:
  • Automatic cache fallback when offline
  • Fibonacci retry backoff (1, 2, 3, 5, 8 min) for background refresh
  • Visual "OFFLINE" watermark on stale data (>1 hour old)
  • Cached location and city name preserved
• No API key required — uses free Open-Meteo API
• No ads, no tracking, no account

Screenshots

Installation

Prerequisites

• Flutter 3.x
• Android SDK
• Android device or emulator

Build & Run

# Get dependencies
flutter pub get
# Generate localizations
flutter gen-l10n
# Build options (via Makefile)
make debug # x86_64 only (68MB) - for emulator
make release # arm64 only (19MB) - for phones
make install # Build release + install on device
make install-debug # Build debug + install on emulator

Install Widget

1. Install the app on your device
2. Open the app and let it load weather data
3. Long-press on home screen → Widgets
4. Find "Meteograph" and drag to home screen
5. Tap widget to refresh data

Project Structure

lib/
├── main.dart # App entry point, edge-to-edge setup
├── generated/version.dart # Generated git version info (gitignored)
├── l10n/ # Localization files (36 languages)
│ ├── app_en.arb # English (template)
│ └── app_*.arb # ar, be, bg, bn, bs, cs, da, de, el, es,
│ # fi, fr, hi, hr, is, it, ja, jv, ka, ko,
│ # mk, nl, no, pa, pl, pt, ro, sk, sq, sv,
│ # ta, tr, uk, vi, zh
├── screens/
│ └── home_screen.dart # Main app screen (both chart panels)
├── services/
│ ├── location_service.dart # GPS + city search + reverse geocoding
│ ├── widget_service.dart # Triggers native widget refresh (WidgetStore)
│ ├── native_svg_service.dart # Method channel to Kotlin (SVG / weather / cache)
│ ├── units_service.dart # Temperature unit and 12/24h logic
│ └── material_you_service.dart # Material You color pass-through
├── theme/
│ └── app_theme.dart # Colors, themes, Material You mapping
└── widgets/
└── native_svg_chart_view.dart # PlatformView wrapper for native SVG
android/app/src/main/kotlin/.../
├── MainActivity.kt # Flutter activity + method channel
├── MeteogramApplication.kt # Receiver registration, alarm schedule
├── MeteogramWidgetProvider.kt # Base widget (48h) — shared logic
├── MeteogramWeeklyWidgetProvider.kt # 7-day variant (extends base)
├── WidgetEventReceiver.kt # Locale / timezone / network receiver
├── WidgetAlarmScheduler.kt # 15-min inexact AlarmManager
├── WidgetAlarmReceiver.kt # Alarm broadcast handler
├── BootCompletedReceiver.kt # Refresh on device boot
├── WidgetUtils.kt # Shared widget helpers
├── WidgetChartColors.kt # Material You color resolver
├── WeatherUpdateWorker.kt # WorkManager periodic refresh (~30 min)
├── WeatherFetcher.kt # Native HTTP client for Open-Meteo
├── WeatherDataParser.kt # Cached-weather parser + chart views
├── SvgChartGenerator.kt # Native SVG generator (single source of truth)
├── MaterialYouColorExtractor.kt # Dynamic color extraction
├── MaterialYouColorWorker.kt # Background color updates
├── SvgChartPlatformView.kt # In-app native SVG rendering
└── SvgChartViewFactory.kt # PlatformView factory
android/app/src/main/res/
├── layout/meteogram_widget.xml # 48h widget layout
├── layout/meteogram_widget_weekly.xml # 7-day widget layout
├── xml/meteogram_widget_info.xml
├── xml/meteogram_widget_weekly_info.xml
└── drawable/widget_background.xml

API

Uses Open-Meteo free APIs (no API key required):

Weather Forecast

GET https://api.open-meteo.com/v1/forecast
?latitude={lat}
&longitude={lon}
&hourly=temperature_2m,precipitation,cloud_cover
&timezone=UTC
&past_hours=32
&forecast_days=7

The 32-hour past window keeps the weekly chart's "now" line at the same fraction of width as the 48-hour chart. The 48-hour chart slices a smaller window (6h past + 46h future) from the same cache.

Returns hourly data for:

• temperature_2m — temperature in Celsius
• precipitation — rain/snow in mm
• cloud_cover — cloud coverage percentage (0-100)

Daylight intensity is computed locally from cloud cover and solar position.

City Search (Geocoding)

GET https://geocoding-api.open-meteo.com/v1/search
?name={query}
&count=8
&language={locale}

The language parameter uses the user's current locale so results come back in their preferred language.

Widget Technical Details

Android Widget

The home screen widgets use:

• AppWidgetProvider (native; two providers — 48h and 7-day weekly)
• RemoteViews for native Android widget rendering
• SVG chart generated in Kotlin (SvgChartGenerator.kt) and rasterised via AndroidSVG
• AlarmManager (~15 min inexact), WorkManager (~30 min with network constraint), and BOOT_COMPLETED for reliable background refresh
• Event receivers for unlock / network / locale / timezone changes

RemoteViews Limitations:

• Only supports: TextView, ImageView, LinearLayout, RelativeLayout, FrameLayout
• Does NOT support: View, Space, custom views

Data Flow

1. Foreground: home_screen.dart → NativeSvgService.fetchWeather() → Kotlin WeatherFetcher pulls from Open-Meteo → caches to SharedPreferences
2. SVG generation: SvgChartGenerator.kt reads the cache and produces an SVG string — single source of truth used by both the in-app chart and both widgets
3. In-app: SVG rendered via native PlatformView (AndroidSVG)
4. Widget: SVG rasterised to a bitmap and shown in an ImageView
5. Background: AlarmManager / WorkManager / BOOT_COMPLETED / event receivers trigger a native refresh + widget re-render, Flutter engine stays off

Customization

Colors

Edit lib/theme/app_theme.dart for the in-app UI and android/app/src/main/kotlin/.../SvgChartGenerator.kt for the chart itself (SvgChartColors.light / SvgChartColors.dark). Example from the Dart side:

staticconst light =MeteogramColors(
temperatureLine:Color(0xFFFF6B6B), // Coral red
precipitationBar:Color(0xFF1A9D92), // Deeper teal (legibility on white)
daylightBar:Color(0xFFFF8F00), // Dark amber
nowIndicator:Color(0xFFFFE66D), // Golden yellow// ...
);

Widget Background

Edit android/app/src/main/res/drawable/widget_background.xml:

<gradientandroid:startColor="#BA1B2838"android:endColor="#BA0D1B2A"android:angle="135" />
<cornersandroid:radius="24dp" />

Adding Languages

1. Create lib/l10n/app_XX.arb (copy from app_en.arb)
2. Translate all strings
3. Run flutter gen-l10n

Supported locales are auto-detected from ARB files.

Dependencies

Package	Purpose
http	API requests (weather, city search)
intl	Locale-aware formatting
flutter_localizations	i18n framework

Location (GPS + reverse geocoding), the widget KV bridge, persistent storage, and Material You theming are all native (over the org.bortnik.meteogram/svg method channel) — no home_widget, geolocator, geocoding, path_provider, or shared_preferences packages. This keeps the project free of any Kotlin-Gradle-Plugin plugin, as required by AGP-9 built-in Kotlin.

License

Business Source License 1.1 - see LICENSE

• Free for non-commercial and personal use
• Commercial use requires a license
• Converts to MIT on 2029-01-01

Contributing

Contributions welcome! Please read the existing code style and test your changes.

Acknowledgments

• Weather data: Open-Meteo
• SVG rendering: AndroidSVG