Shaders: Anime4K presets in-session and in Settings

Vendored Anime4K v4.0.1 GLSL (MIT), extracted to app support once per
version. Presets A/B/C/A+A/B+B/C+A in HQ and Fast per Anime4K's mpv
templates, plus custom files. Shader button in the video controls
(works in fullscreen), Ctrl+1..6 / Ctrl+0, live apply with read-back,
failures fall back to Off with a toast. Render mode detected from
mpv's GL log; warns when on the software path. Docs include the
Jellyfin client section.

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

apps/desktop/lib/src/shaders/shader_menu.dart

@@ -0,0 +1,197 @@
+import 'package:flutter/material.dart';
+import 'package:signals/signals_flutter.dart';
+
+import '../playback/playback_controller.dart';
+import '../state/settings.dart';
+import 'shader_presets.dart';
+
+/// A shader pick from the menu; a null quality keeps the saved one.
+typedef ShaderPick = (ShaderPreset, ShaderQuality?);
+
+/// Compact shader button for the video controls bar (normal and
+/// fullscreen). Opens a small menu: Off, the six Anime4K modes with
+/// HQ / Fast, Custom. The menu is a route, so it outlives the controls
+/// bar hiding under it; [onPick] runs on the caller's side.
+class ShaderControlButton extends StatelessWidget {
+  final FocusNode focusNode;
+  final ReadonlySignal<RenderMode> renderMode;
+  final void Function(ShaderPreset preset, ShaderQuality? quality) onPick;
+  final ValueChanged<bool>? onMenuOpen;
+  const ShaderControlButton({
+    super.key,
+    required this.focusNode,
+    required this.renderMode,
+    required this.onPick,
+    this.onMenuOpen,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    final s = AppSettings.instance;
+    return SignalBuilder(builder: (context) {
+      final preset = s.shaderPreset.value;
+      final quality = s.shaderQuality.value;
+      final short = switch (preset) {
+        ShaderPreset.off => 'Shaders',
+        ShaderPreset.custom => 'Custom',
+        _ => '${preset.label.replaceFirst('Mode ', '')} ${quality.label}',
+      };
+      return Tooltip(
+        message: 'Video shaders (Ctrl+1..6, Ctrl+0 off)',
+        child: TextButton.icon(
+          focusNode: focusNode,
+          style: TextButton.styleFrom(
+            foregroundColor:
+                preset == ShaderPreset.off ? Colors.white : Colors.amberAccent,
+            padding: const EdgeInsets.symmetric(horizontal: 8),
+            tapTargetSize: MaterialTapTargetSize.shrinkWrap,
+          ),
+          onPressed: () => _open(context),
+          icon: const Icon(Icons.auto_awesome, size: 16),
+          label: Text(short, style: const TextStyle(fontSize: 12)),
+        ),
+      );
+    });
+  }
+
+  Future<void> _open(BuildContext context) async {
+    final s = AppSettings.instance;
+    final preset = s.shaderPreset.peek();
+    final quality = s.shaderQuality.peek();
+    final hasCustom = s.customShaders.peek().isNotEmpty;
+    final button = context.findRenderObject() as RenderBox;
+    final overlay =
+        Navigator.of(context).overlay!.context.findRenderObject() as RenderBox;
+    final position = RelativeRect.fromRect(
+      Rect.fromPoints(
+        button.localToGlobal(Offset.zero, ancestor: overlay),
+        button.localToGlobal(button.size.bottomRight(Offset.zero),
+            ancestor: overlay),
+      ),
+      Offset.zero & overlay.size,
+    );
+    final software = renderMode.peek() == RenderMode.software;
+    onMenuOpen?.call(true);
+    final pick = await showMenu<ShaderPick>(
+      context: context,
+      position: position,
+      popUpAnimationStyle: AnimationStyle.noAnimation,
+      // Wider than Material's 280 px cap: the mode rows hold two chips.
+      constraints: const BoxConstraints(minWidth: 340, maxWidth: 340),
+      items: [
+        if (software)
+          const PopupMenuItem(
+            enabled: false,
+            height: 32,
+            child: Text('Software rendering: shaders have no effect',
+                style: TextStyle(fontSize: 12, color: Colors.orange)),
+          ),
+        CheckedPopupMenuItem(
+          value: (ShaderPreset.off, null),
+          checked: preset == ShaderPreset.off,
+          height: 36,
+          child: const _Row(label: 'Off', keys: 'Ctrl+0'),
+        ),
+        for (final (i, mode) in ShaderPreset.modes.indexed)
+          _ModeEntry(
+            mode: mode,
+            keys: 'Ctrl+${i + 1}',
+            current: preset == mode ? quality : null,
+          ),
+        CheckedPopupMenuItem(
+          value: (ShaderPreset.custom, null),
+          checked: preset == ShaderPreset.custom,
+          enabled: hasCustom,
+          height: 36,
+          child: Text(hasCustom
+              ? 'Custom shaders'
+              : 'Custom shaders (pick files in Settings)'),
+        ),
+      ],
+    );
+    onMenuOpen?.call(false);
+    if (pick != null) onPick(pick.$1, pick.$2);
+  }
+}
+
+class _Row extends StatelessWidget {
+  final String label;
+  final String keys;
+  const _Row({required this.label, required this.keys});
+
+  @override
+  Widget build(BuildContext context) {
+    return Row(
+      children: [
+        Expanded(child: Text(label)),
+        Text(keys, style: const TextStyle(fontSize: 11, color: Colors.grey)),
+      ],
+    );
+  }
+}
+
+/// One Anime4K mode: the row picks it with the saved quality, the two
+/// chips pick a quality explicitly.
+class _ModeEntry extends PopupMenuEntry<ShaderPick> {
+  final ShaderPreset mode;
+  final String keys;
+  /// The active quality when this mode is the current one.
+  final ShaderQuality? current;
+  const _ModeEntry({
+    required this.mode,
+    required this.keys,
+    required this.current,
+  });
+
+  @override
+  double get height => 36;
+
+  @override
+  bool represents(ShaderPick? value) => value?.$1 == mode;
+
+  @override
+  State<_ModeEntry> createState() => _ModeEntryState();
+}
+
+class _ModeEntryState extends State<_ModeEntry> {
+  @override
+  Widget build(BuildContext context) {
+    final w = widget;
+    final theme = Theme.of(context);
+    void pick(ShaderQuality? q) => Navigator.of(context).pop((w.mode, q));
+    return InkWell(
+      onTap: () => pick(null),
+      child: Container(
+        height: w.height,
+        padding: const EdgeInsets.symmetric(horizontal: 12),
+        child: Row(
+          children: [
+            SizedBox(
+              width: 36,
+              child: w.current != null
+                  ? Icon(Icons.done, size: 20, color: theme.colorScheme.primary)
+                  : null,
+            ),
+            SizedBox(width: 96, child: Text(w.mode.label)),
+            for (final q in ShaderQuality.values)
+              Padding(
+                padding: const EdgeInsets.only(right: 4),
+                child: ChoiceChip(
+                  label: Text(q.label, style: const TextStyle(fontSize: 11)),
+                  selected: w.current == q,
+                  showCheckmark: false,
+                  visualDensity: VisualDensity.compact,
+                  materialTapTargetSize: MaterialTapTargetSize.shrinkWrap,
+                  labelPadding: const EdgeInsets.symmetric(horizontal: 4),
+                  onSelected: (_) => pick(q),
+                ),
+              ),
+            const Spacer(),
+            Text(w.keys,
+                style: const TextStyle(fontSize: 11, color: Colors.grey)),
+          ],
+        ),
+      ),
+    );
+  }
+}