GlassAppBar class

A navigation bar layout widget following Apple's iOS 26 design patterns.

GlassAppBar renders a solid or transparent bar with leading widget, centered title, and trailing actions. Glass effects belong on the individual interactive elements (buttons, pills) — not the bar surface itself. This matches iOS 26's navigation bar where the bar is a simple layout container and glass is reserved for buttons.

Large-title collapse (iOS 26 pattern)

Pair with GlassLargeTitle and GlassLargeTitleController to get automatic cross-fade between the large title (in the scroll view) and the inline bar title — with zero boilerplate:

final _titleController = GlassLargeTitleController();

GlassScaffold(
  appBar: GlassAppBar(
    title: Text('Chats'),
    largeTitleController: _titleController,   // ← fades in as user scrolls
  ),
  body: CustomScrollView(
    controller: _titleController.scrollController,
    slivers: [
      GlassLargeTitle(text: 'Chats', controller: _titleController),
      // ... content slivers
    ],
  ),
)

Transparent (default — iOS 26 style)

GlassAppBar(
  title: Text('Messages'),
  leading: GlassButton(
    icon: Icon(CupertinoIcons.back),
    onTap: () => Navigator.pop(context),
  ),
)

Solid background (WhatsApp / Player style)

GlassAppBar(
  backgroundColor: Color(0xFF2C2C2E),
  title: Text('Now Playing'),
  leading: GlassButton(
    icon: Icon(CupertinoIcons.back),
    onTap: () => Navigator.pop(context),
  ),
)

Custom button settings (all buttons inherit)

GlassAppBar(
  buttonSettings: LiquidGlassSettings(
    glassColor: Color(0x33FFFFFF),
    thickness: 20,
  ),
  leading: GlassButton(...),   // inherits buttonSettings
  actions: [GlassButton(...)], // inherits buttonSettings
)

This widget implements ObstructingPreferredSizeWidget for use in both Scaffold.appBar and CupertinoPageScaffold.navigationBar.