mikkeli
31a844bb94
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>
49 lines
2.0 KiB
Dart
49 lines
2.0 KiB
Dart
// Auto dark/bright from the sun: dark once it is far enough below the horizon, at the
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// tablet's own rough location (Android's, not the Orin's: the tablet stands on its own).
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// Google Maps on this tablet does the same (it reads no light sensor; checked). Needs no
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// sensor; does not know about tunnels or car parks.
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import 'dart:math' as math;
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import 'package:flutter/services.dart';
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/// The tablet's newest known location, roughly, from MainActivity; null without one
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/// (or before location is granted: the first call asks).
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Future<(double, double)?> androidLocation() async {
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try {
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final v = await const MethodChannel('yukart/location')
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.invokeListMethod<double>('last');
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return v == null || v.length < 2 ? null : (v[0], v[1]);
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} catch (_) {
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return null; // No Android side (tests, desktop).
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}
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}
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/// Dark while the sun is lower than this (degrees; sunset is -0.8, civil dusk -6).
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const darkBelowDeg = -4.0;
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/// The sun's elevation above the horizon, in degrees, at [lat], [lon] (degrees, east
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/// positive) and [time]. The usual low-precision formulae (the Astronomical Almanac's,
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/// as NOAA uses them): within about a degree, plenty for this.
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double sunElevation(double lat, double lon, DateTime time) {
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double rad(double d) => d * math.pi / 180;
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double deg(double r) => r * 180 / math.pi;
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final d =
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time.toUtc().millisecondsSinceEpoch / 86400000 + 2440587.5 - 2451545.0;
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final g = rad(357.529 + 0.98560028 * d); // mean anomaly
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final q = 280.459 + 0.98564736 * d; // mean longitude
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final l = rad(q + 1.915 * math.sin(g) + 0.020 * math.sin(2 * g));
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final e = rad(23.439 - 0.00000036 * d); // obliquity
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final ra = math.atan2(math.cos(e) * math.sin(l), math.cos(l));
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final dec = math.asin(math.sin(e) * math.sin(l));
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final gmst = (18.697374558 + 24.06570982441908 * d) % 24;
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final ha = rad(gmst * 15 + lon) - ra;
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final phi = rad(lat);
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return deg(
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math.asin(
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math.sin(phi) * math.sin(dec) +
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math.cos(phi) * math.cos(dec) * math.cos(ha),
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),
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);
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}
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