What the app declares

Some things the glass needs to know are not in the render tree, and Flutter does not pass some platform settings on. g1455 ships no platform code to go and read them, so the application declares them, all as parameters of GlassHost. Everything here is optional: leave a declaration out and you get a safe default.

What is behind the glass

Components such as GlassBar and GlassCard choose black or white text. To choose well, the host needs to know what the glass sits over:

• backdrop: the screen's average background colour, for a flat background. It is also what the opaque tier fills with, so declare it whenever you might use that tier.
• richBackdrop: true for an image, a video, a map or a feed. Labels are then chosen for the worst case over any backdrop.
• minLabelContrast: a contrast floor, such as kTextContrastAA (4.5, WCAG AA for body text). When the finish cannot reach it, the glass is dimmed just enough to do so.

Without any of these, labels are picked against the worst case, and in debug the package warns once when a finish cannot be read over it. More on Legibility & theme.

Reduce transparency

Flutter does not expose the operating system's Reduce Transparency switch. Read it natively and pass it to a GlassTierPolicy, which answers with the opaque tier:

GlassHost(
  backdrop: const Color(0xFF101014), // the opaque tier fills with this
  tier: GlassTierPolicy(reduceTransparency: reduceTransparency).choose(),
  child: child,
)

The same policy takes a ceiling for low-end devices, such as GlassTier.cheap. The package never switches tiers on its own.

Increase contrast

GlassHost.highContrast draws an opaque, visible outline instead of the subtle rim. On iOS and on Android 34 and later the host already reads it from MediaQuery. On macOS the engine does not pass it on, so read it natively and pass highContrast: true.

Thermal state

Pass the device's thermal state as a GlassThermalState (nominal, fair, serious, critical, Apple's four names). Under serious and critical the host may reuse a slightly stale capture for a frame or two on screens that change. Blurry finishes tolerate that; clear gets none. Tiers are never changed by thermals.

On Android, map PowerManager's thermal status: NONE to nominal, LIGHT and MODERATE to fair, SEVERE to serious, and CRITICAL, EMERGENCY and SHUTDOWN to critical.

Hardware

GlassHost.hardware says which device family's measurements apply. GlassHardware.detect() returns appleMetal on iOS and macOS and unmeasured elsewhere, because Dart cannot name the GPU. Declare adrenoVulkan only for a Snapdragon with an Adreno 830-class GPU. Undeclared hardware gets the same behaviour with no price attached: it changes reported costs and the default texture limit, never correctness.

Code

import 'package:flutter/material.dart';
import 'package:g1455/g1455.dart';

/// The settings the package cannot read for itself. Fill them from your own
/// platform code (a method channel, a plugin) and rebuild when they change.
class DeviceSignals {
  const DeviceSignals({
    this.reduceTransparency = false,
    this.increaseContrast,
    this.thermal = GlassThermalState.nominal,
    this.lowEndDevice = false,
  });

  final bool reduceTransparency;
  final bool? increaseContrast; // null: let the host read MediaQuery
  final GlassThermalState thermal;
  final bool lowEndDevice;
}

class DeclaredApp extends StatelessWidget {
  const DeclaredApp({super.key, required this.signals, required this.home});

  final DeviceSignals signals;
  final Widget home;

  @override
  Widget build(BuildContext context) => MaterialApp(
    builder: (BuildContext context, Widget? child) => GlassHost(
      // What is behind the glass: a feed over a near-black page.
      backdrop: const Color(0xFF101014),
      richBackdrop: true,
      minLabelContrast: kTextContrastAA,
      // Reduce transparency gives the opaque tier; a low-end device stops at cheap.
      tier: GlassTierPolicy(
        reduceTransparency: signals.reduceTransparency,
        ceiling: signals.lowEndDevice ? GlassTier.cheap : null,
      ).choose(),
      highContrast: signals.increaseContrast,
      thermal: signals.thermal,
      hardware: GlassHardware.detect(),
      child: child!,
    ),
    home: home,
  );
}