Auto dark/bright follows the sun at the tablet's own location

Without a light sensor an app may read (the Redmi Pad SE has none), auto is dark while
the sun is more than 4° below the horizon (lib/theme/sun.dart), at Android's coarse
location, polled and kept across restarts. The tablet's own, not the Orin's GNSS: the
tablet has its own GNSS and cellular. Android's dark theme is the last fallback.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

android/app/src/main/AndroidManifest.xml

@@ -3,6 +3,8 @@
     <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
     <!-- requestNetwork for the USB (NCM) Ethernet link to the Orin -->
     <uses-permission android:name="android.permission.CHANGE_NETWORK_STATE"/>
+    <!-- Where the tablet is, roughly: for the sun (auto dark/bright, lib/theme/sun.dart). -->
+    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>
     <application
         android:label="Yukart"
         android:name="${applicationName}"

android/app/src/main/kotlin/dev/yukart/display/MainActivity.kt

@@ -1,15 +1,19 @@
 package dev.yukart.display
 
+import android.Manifest
 import android.content.Context
 import android.content.Intent
+import android.content.pm.PackageManager
 import android.hardware.Sensor
 import android.hardware.SensorEvent
 import android.hardware.SensorEventListener
 import android.hardware.SensorManager
+import android.location.LocationManager
 import android.net.ConnectivityManager
 import android.net.Network
 import android.net.NetworkCapabilities
 import android.net.NetworkRequest
+import android.os.Build
 import android.os.Bundle
 import android.view.WindowManager
 import io.flutter.embedding.android.FlutterActivity
@@ -29,6 +33,7 @@ import io.flutter.plugin.common.MethodChannel
  *
  * Also the light sensor, for auto dark/bright (lib/theme/light.dart): lux on `yukart/light`
  * while Dart listens, where the device lets apps read one (the Redmi Pad SE does not).
+ * And, for the sun instead, the tablet's own rough location on `yukart/location`.
  *
  * Also a development hook: `am start -n dev.yukart.display/.MainActivity --es linktest [dl:|bi:]<label>[@<host>]`
  * runs the link test (lib/linktest.dart) without touching the screen.
@@ -39,6 +44,7 @@ class MainActivity : FlutterActivity() {
     private var ethernet: Network? = null
     private var wantBinding = false
     private var pendingLinkTest: String? = null
+    private var askedLocation = false
 
     private val callback = object : ConnectivityManager.NetworkCallback() {
         override fun onAvailable(network: Network) {
@@ -90,10 +96,38 @@ class MainActivity : FlutterActivity() {
             .build()
         cm.requestNetwork(request, callback)
 
+        MethodChannel(flutterEngine.dartExecutor.binaryMessenger, "yukart/location").setMethodCallHandler { call, result ->
+            if (call.method == "last") result.success(lastLocation()) else result.notImplemented()
+        }
+
         EventChannel(flutterEngine.dartExecutor.binaryMessenger, "yukart/light")
             .setStreamHandler(LightStream(getSystemService(Context.SENSOR_SERVICE) as SensorManager))
     }
 
+    /**
+     * [lat, lon] of the newest location Android has (other apps' fixes included), or null.
+     * Asks for coarse location the first time; with none known, asks for one, which the
+     * next call sees.
+     */
+    private fun lastLocation(): List<Double>? {
+        if (checkSelfPermission(Manifest.permission.ACCESS_COARSE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
+            if (!askedLocation) {
+                askedLocation = true
+                requestPermissions(arrayOf(Manifest.permission.ACCESS_COARSE_LOCATION), 1)
+            }
+            return null
+        }
+        val lm = getSystemService(Context.LOCATION_SERVICE) as LocationManager
+        val enabled = lm.getProviders(true)
+        val best = enabled.mapNotNull { runCatching { lm.getLastKnownLocation(it) }.getOrNull() }.maxByOrNull { it.time }
+        if (best == null && Build.VERSION.SDK_INT >= Build.VERSION_CODES.R) {
+            listOf("fused", LocationManager.NETWORK_PROVIDER, LocationManager.GPS_PROVIDER)
+                .firstOrNull { it in enabled }
+                ?.let { runCatching { lm.getCurrentLocation(it, null, mainExecutor) {} } }
+        }
+        return best?.let { listOf(it.latitude, it.longitude) }
+    }
+
     /** Lux from the default light sensor while listened to; an error at once without one, or when refused. */
     private class LightStream(private val sm: SensorManager) : EventChannel.StreamHandler {
         private var listener: SensorEventListener? = null

docs/impl/plans/DASH-NEXT.md

@@ -81,10 +81,15 @@ where the device lets an app read one (`theme/light.dart`: dark at ≤ 15 lux, b
 held 5 s; Settings shows the reading). **The Redmi Pad SE does not:** its only light sensor,
 `camera_light_Sensor`, is derived by Xiaomi from the front camera, and `registerListener` refuses
 apps at every rate (only the system's auto-brightness reads it). Its automatic brightness is not
-exposed either (`screen_brightness` is the manual level). Other lux sources, if wanted:
-the Orin's camera (its exposure and gain say how bright the road is; svc-vision would publish
-it), opening the tablet's front camera ourselves (camera permission, the in-use dot, and the
-camera's power), or sunrise and sunset from GNSS position and time (no sensor; tunnels ignored).
+exposed either (`screen_brightness` is the manual level). Google Maps here
+reads no light sensor either (checked while it navigated in its night colours): it goes by
+time and place, and tunnels from map data.
+
+**Sun, done (2026-10-15):** without a light sensor, auto follows the sun at the tablet's own
+rough location (Android's coarse location, polled; kept across restarts; not the Orin's GNSS,
+since the tablet has its own GNSS and cellular): dark below −4° (`theme/sun.dart`). Android's
+dark theme is the last fallback, before any location is known. Tunnels and car parks are not
+seen; the quick button covers them.
 What was asked:
 
 Today the variant is a switch (the Dash's top-right button, and Settings). Wanted:

lib/README.md

@@ -42,7 +42,7 @@ pirate-station-aide's (main views, then the rarely used ones grouped as Tools).
   `onFill(colour)` (text on a fill). No widget names a colour. Themes are JSON in `assets/themes/`, `rei` by
   default; smart-serow's four-key files still load (their `highlight` is `alarm`).
 - **Dark or bright.** `Themes.mode` is `auto` (a light sensor where the device allows one, `theme/light.dart`;
-  else Android's dark theme, schedule included), `dark` or
+  else the sun at the tablet's own location, `theme/sun.dart`; else Android's dark theme), `dark` or
   `bright`, chosen in Settings and kept across restarts. The status bar's button holds the other variant;
   a long press there is auto again.
 - **Cosmetic fonts are opt-in.** A widget that wants the HUD face names `fontFamily: hudFont` in its own

lib/main.dart

@@ -1,16 +1,18 @@
 // Yukart display: the tablet app. Starts the link to the Orin and hands the screen to
 // the shell (lib/shell.dart). Code layout: lib/README.md.
 
+import 'dart:async';
+
 import 'package:flutter/material.dart';
 
 import 'link/boundary.dart';
 import 'link/net.dart';
-import 'link/reading.dart';
 import 'pages/link_test.dart';
 import 'shell.dart';
 import 'shell_scope.dart';
 import 'theme/light.dart';
 import 'theme/palette.dart';
+import 'theme/sun.dart';
 
 /// Override for development, e.g. `--dart-define=YUKART_GW=ws://halogen.local:7700/`.
 const defaultUrl = String.fromEnvironment(
@@ -25,14 +27,15 @@ Future<void> main() async {
   final usb = UsbLink();
   await usb.bindFor(Uri.parse(defaultUrl));
   final boundary = Boundary(defaultUrl)..start();
-  // The sun, for auto dark/bright: the car's position while GNSS has one.
-  boundary.addListener(() {
-    final lat = Reading.of(boundary, 'gnss_lat');
-    final lon = Reading.of(boundary, 'gnss_lon');
-    if (!lat.dim && !lon.dim && lat.number != null && lon.number != null) {
-      themes.setPosition(lat.number!, lon.number!);
+  // The sun, for auto dark/bright: the tablet's own location, every minute until there
+  // is one (the first ask brings up the permission), then every ten.
+  Future<void> locate() async {
+    final p = await androidLocation();
+    if (p != null) themes.setPosition(p.$1, p.$2);
+    Timer(Duration(minutes: p == null ? 1 : 10), locate);
   }
-  });
+
+  locate();
   final linkTest = LinkTest(usb);
   // Development hook: `am start ... --es linktest [dl:|bi:]<label>[@<host>]` runs the test
   // (`dl:` the download series, `bi:` burst latency against idle gaps), on the gateway's host unless one is given.

lib/pages/settings.dart

@@ -65,9 +65,9 @@ class SettingsPage extends StatelessWidget {
                       ? 'now ${lux.toStringAsFixed(lux < 10 ? 1 : 0)} lux; dark at '
                             '${LightSwitch.darkAt.round()} or less, bright from ${LightSwitch.brightAt.round()}'
                       : sun != null
-                      ? 'now ${sun.round()}° above the horizon at the last GNSS position; '
-                            'dark below ${darkBelowDeg.round()}°'
-                      : 'no GNSS position yet';
+                      ? 'the sun is ${sun.abs().round()}° ${sun < 0 ? 'below' : 'above'} the horizon here; '
+                            'dark from ${(-darkBelowDeg).round()}° below'
+                      : 'no location yet';
                   return Text(
                     'Auto follows ${themes.autoSource} ($now). '
                     'The status bar button holds one; a long press there is auto again.',

lib/theme/palette.dart

@@ -127,7 +127,7 @@ enum VariantMode { auto, dark, bright }
 
 /// A theme: both variants, and which one is showing. Listen to it to follow a switch.
 /// In auto it follows a light sensor ([followLight]) where the device lets an app read
-/// one; else the sun at the car's last position ([setPosition]); else Android's dark
+/// one; else the sun at the tablet's last location ([setPosition]); else Android's dark
 /// theme (by hand or on its schedule). The mode and the position are kept across restarts.
 class Themes extends ChangeNotifier with WidgetsBindingObserver {
   Themes(
@@ -210,7 +210,7 @@ class Themes extends ChangeNotifier with WidgetsBindingObserver {
   bool? _sunDark;
   late final Timer _sunTimer;
 
-  /// The car's position, for the sun. Kept (to 0.1°, about 10 km: plenty for the sun)
+  /// The tablet's location, for the sun. Kept (to 0.1°, about 10 km: plenty for the sun)
   /// so auto knows the sun before the first fix.
   void setPosition(double lat, double lon) {
     double r(double x) => (x * 10).round() / 10;

lib/theme/sun.dart

@@ -0,0 +1,48 @@
+// Auto dark/bright from the sun: dark once it is far enough below the horizon, at the
+// tablet's own rough location (Android's, not the Orin's: the tablet stands on its own).
+// Google Maps on this tablet does the same (it reads no light sensor; checked). Needs no
+// sensor; does not know about tunnels or car parks.
+
+import 'dart:math' as math;
+
+import 'package:flutter/services.dart';
+
+/// The tablet's newest known location, roughly, from MainActivity; null without one
+/// (or before location is granted: the first call asks).
+Future<(double, double)?> androidLocation() async {
+  try {
+    final v = await const MethodChannel('yukart/location')
+        .invokeListMethod<double>('last');
+    return v == null || v.length < 2 ? null : (v[0], v[1]);
+  } catch (_) {
+    return null; // No Android side (tests, desktop).
+  }
+}
+
+/// Dark while the sun is lower than this (degrees; sunset is -0.8, civil dusk -6).
+const darkBelowDeg = -4.0;
+
+/// The sun's elevation above the horizon, in degrees, at [lat], [lon] (degrees, east
+/// positive) and [time]. The usual low-precision formulae (the Astronomical Almanac's,
+/// as NOAA uses them): within about a degree, plenty for this.
+double sunElevation(double lat, double lon, DateTime time) {
+  double rad(double d) => d * math.pi / 180;
+  double deg(double r) => r * 180 / math.pi;
+  final d =
+      time.toUtc().millisecondsSinceEpoch / 86400000 + 2440587.5 - 2451545.0;
+  final g = rad(357.529 + 0.98560028 * d); // mean anomaly
+  final q = 280.459 + 0.98564736 * d; // mean longitude
+  final l = rad(q + 1.915 * math.sin(g) + 0.020 * math.sin(2 * g));
+  final e = rad(23.439 - 0.00000036 * d); // obliquity
+  final ra = math.atan2(math.cos(e) * math.sin(l), math.cos(l));
+  final dec = math.asin(math.sin(e) * math.sin(l));
+  final gmst = (18.697374558 + 24.06570982441908 * d) % 24;
+  final ha = rad(gmst * 15 + lon) - ra;
+  final phi = rad(lat);
+  return deg(
+    math.asin(
+      math.sin(phi) * math.sin(dec) +
+          math.cos(phi) * math.cos(dec) * math.cos(ha),
+    ),
+  );
+}

test/palette_test.dart

@@ -2,6 +2,7 @@ import 'dart:async';
 
 import 'package:display/theme/light.dart';
 import 'package:display/theme/palette.dart';
+import 'package:display/theme/sun.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:shared_preferences/shared_preferences.dart';
@@ -69,5 +70,57 @@ void main() {
       const Duration(seconds: 6),
     ); // no new reading: the timer ends the hold
     expect(t.isDark, isTrue);
+    t.dispose();
   });
+
+  test(
+    'the sun: high at noon, below at midnight, sets near the almanac time',
+    () {
+      // Tokyo, 2026-06-21: noon (03:00 UTC) about 77°, midnight well below.
+      expect(
+        sunElevation(35.68, 139.77, DateTime.utc(2026, 6, 21, 2, 43)),
+        closeTo(77.7, 1),
+      );
+      expect(
+        sunElevation(35.68, 139.77, DateTime.utc(2026, 6, 21, 15)),
+        lessThan(-20),
+      );
+      // Helsinki, 2026-10-15: sunset 18:14 EEST (15:14 UTC): -0.8° there.
+      expect(
+        sunElevation(60.17, 24.94, DateTime.utc(2026, 10, 15, 15, 14)),
+        closeTo(-0.8, 0.6),
+      );
+    },
+  );
+
+  test(
+    'auto: the sun before Android, the light sensor before the sun',
+    () async {
+      SharedPreferences.setMockInitialValues({});
+      final prefs = await SharedPreferences.getInstance();
+      dispatcher.platformBrightnessTestValue = Brightness.light;
+      var now = DateTime.utc(2026, 6, 21, 15); // Tokyo midnight
+      final t = Themes(
+        't',
+        Palette.fallbackDark,
+        Palette.fallbackBright,
+        prefs,
+        () => now,
+      );
+      expect((t.isDark, t.autoSource), (false, "Android's dark theme"));
+      t.setPosition(35.68, 139.77);
+      expect((t.isDark, t.autoSource), (true, 'the sun'));
+      now = DateTime.utc(2026, 6, 21, 3);
+      final again = Themes(
+        't',
+        Palette.fallbackDark,
+        Palette.fallbackBright,
+        prefs,
+        () => now,
+      );
+      expect(again.isDark, isFalse); // position kept; Tokyo noon
+      t.dispose();
+      again.dispose();
+    },
+  );
 }