feat(player): animate Material seek bar with expressive waves

lib/screens/now_playing_screen.dart

@@ -2724,6 +2724,7 @@ class _PlaybackControls extends ConsumerWidget {
                         duration: duration,
                         onSeek: controller.seek,
                         preview: seekPreview,
+                        playing: isPlaying && !isLoading,
                       ),
                     ),
                     Padding(

lib/widgets/expressive_seek_track.dart

@@ -0,0 +1,181 @@
+import 'dart:math' as math;
+
+import 'package:flutter/material.dart';
+import 'package:material_3_expressive/components/sliders/components/m3e_slider_track_painter.dart';
+import 'package:material_3_expressive/material_3_expressive.dart';
+
+/// Expressive track motion around the native slider's seeking and accessibility.
+class ExpressiveSeekTrack extends StatefulWidget {
+  const ExpressiveSeekTrack({
+    super.key,
+    required this.playing,
+    required this.child,
+  });
+
+  final bool playing;
+  final Widget child;
+
+  @override
+  State<ExpressiveSeekTrack> createState() => _ExpressiveSeekTrackState();
+}
+
+class _ExpressiveSeekTrackState extends State<ExpressiveSeekTrack>
+    with TickerProviderStateMixin {
+  late final _phase = AnimationController(
+    vsync: this,
+    duration: const Duration(milliseconds: 1800),
+  );
+  late final _amplitude =
+      AnimationController(
+        vsync: this,
+        duration: const Duration(milliseconds: 300),
+      )..addStatusListener((status) {
+        if (status == AnimationStatus.dismissed) _phase.stop();
+      });
+  late final _animation = Listenable.merge([_phase, _amplitude]);
+  bool _motionEnabled = false;
+
+  @override
+  void didChangeDependencies() {
+    super.didChangeDependencies();
+    _motionEnabled =
+        !MediaQuery.disableAnimationsOf(context) &&
+        TickerMode.valuesOf(context).enabled;
+    _syncAnimation();
+  }
+
+  @override
+  void didUpdateWidget(ExpressiveSeekTrack oldWidget) {
+    super.didUpdateWidget(oldWidget);
+    if (oldWidget.playing != widget.playing) _syncAnimation();
+  }
+
+  void _syncAnimation() {
+    if (!_motionEnabled) {
+      _phase.stop();
+      _amplitude.value = 0;
+    } else if (widget.playing) {
+      if (!_phase.isAnimating) _phase.repeat();
+      _amplitude.forward();
+    } else {
+      _amplitude.reverse();
+      if (_amplitude.isDismissed) _phase.stop();
+    }
+  }
+
+  @override
+  void dispose() {
+    _amplitude.dispose();
+    _phase.dispose();
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) => RepaintBoundary(
+    child: AnimatedBuilder(
+      animation: _animation,
+      child: widget.child,
+      builder: (context, child) => SliderTheme(
+        data: SliderTheme.of(context).copyWith(
+          trackHeight: 4,
+          trackShape: ExpressiveSeekTrackShape(
+            phase: _phase.value * 2 * math.pi,
+            amplitude: Curves.easeInOutCubic.transform(_amplitude.value),
+          ),
+          thumbShape: const HandleThumbShape(),
+          thumbSize: const WidgetStatePropertyAll(Size(4, 24)),
+        ),
+        child: child!,
+      ),
+    ),
+  );
+}
+
+/// Uses the package's wave renderer without changing the slider gesture cycle.
+class ExpressiveSeekTrackShape extends RoundedRectSliderTrackShape {
+  const ExpressiveSeekTrackShape({
+    required this.phase,
+    required this.amplitude,
+  });
+
+  final double phase;
+  final double amplitude;
+
+  @override
+  void paint(
+    PaintingContext context,
+    Offset offset, {
+    required RenderBox parentBox,
+    required SliderThemeData sliderTheme,
+    required Animation<double> enableAnimation,
+    required TextDirection textDirection,
+    required Offset thumbCenter,
+    Offset? secondaryOffset,
+    bool isDiscrete = false,
+    bool isEnabled = false,
+    double additionalActiveTrackHeight = 2,
+  }) {
+    final track = getPreferredRect(
+      parentBox: parentBox,
+      offset: offset,
+      sliderTheme: sliderTheme,
+      isEnabled: isEnabled,
+      isDiscrete: isDiscrete,
+    );
+    if (track.isEmpty) return;
+    final rtl = textDirection == TextDirection.rtl;
+    final fraction =
+        ((rtl ? track.right - thumbCenter.dx : thumbCenter.dx - track.left) /
+                track.width)
+            .clamp(0.0, 1.0);
+    final active = Color.lerp(
+      sliderTheme.disabledActiveTrackColor,
+      sliderTheme.activeTrackColor,
+      enableAnimation.value,
+    )!;
+    final inactive = Color.lerp(
+      sliderTheme.disabledInactiveTrackColor,
+      sliderTheme.inactiveTrackColor,
+      enableAnimation.value,
+    )!;
+    final painter = M3ESliderTrackPainter(
+      mode: M3ESliderPaintMode.single,
+      trackKind: M3ESliderTrackKind.standard,
+      activeStartFraction: 0,
+      activeEndFraction: fraction,
+      tickFractions: const [],
+      colors: M3ESliderColors(
+        thumb: active,
+        activeTrack: active,
+        inactiveTrack: inactive,
+        activeTick: inactive,
+        inactiveTick: active,
+        stopIndicator: active,
+        valueIndicator: active,
+        valueIndicatorLabel: inactive,
+      ),
+      trackHeight: track.height,
+      handleGap: 6,
+      handleThickness: 4,
+      insideCornerSize: 2,
+      cornerRadius: 2,
+      stopIndicatorSize: 4,
+      tickSize: 0,
+      edgeInset: 2,
+      axis: Axis.horizontal,
+      // Mirror the complete logical track, including waves and the end marker.
+      textDirection: TextDirection.ltr,
+      isWavy: amplitude > 0,
+      waveAmplitude: 3,
+      wavelength: 40,
+      phase: phase,
+      amplitudeFactor: amplitude,
+    );
+    final canvas = context.canvas;
+    canvas.save();
+    canvas.translate(rtl ? track.right : track.left, track.top);
+    if (rtl) canvas.scale(-1, 1);
+    painter.paint(canvas, track.size);
+    canvas.restore();
+  }
+}

lib/widgets/playback_seek_slider.dart

@@ -1,6 +1,7 @@
 import 'package:flutter/material.dart';
 import 'package:spotiflac_android/theme/mornye_theme.dart';
 import 'package:spotiflac_android/utils/playback_seek_preview.dart';
+import 'package:spotiflac_android/widgets/expressive_seek_track.dart';
 import 'package:spotiflac_android/widgets/mornye_player_slider.dart';
 
 /// Previews scrubbing locally and seeks once when the gesture ends.
@@ -9,6 +10,7 @@ class PlaybackSeekSlider extends StatefulWidget {
   final Duration duration;
   final Future<void> Function(Duration) onSeek;
   final PlaybackSeekPreview? preview;
+  final bool playing;
 
   const PlaybackSeekSlider({
     super.key,
@@ -16,6 +18,7 @@ class PlaybackSeekSlider extends StatefulWidget {
     required this.duration,
     required this.onSeek,
     this.preview,
+    this.playing = false,
   });
 
   @override
@@ -118,17 +121,24 @@ class _PlaybackSeekSliderState extends State<PlaybackSeekSlider> {
         ),
       );
     }
-    return Slider(
-      value: enabled
-          ? (_previewMs ?? widget.position.inMilliseconds.toDouble()).clamp(
-              0,
-              maxMs,
-            )
-          : 0,
-      max: maxMs,
-      onChangeStart: enabled ? _start : null,
-      onChanged: enabled ? _preview : null,
-      onChangeEnd: enabled ? _commit : null,
+    return ExpressiveSeekTrack(
+      playing:
+          widget.playing &&
+          enabled &&
+          widget.position < widget.duration &&
+          _previewMs == null,
+      child: Slider(
+        value: enabled
+            ? (_previewMs ?? widget.position.inMilliseconds.toDouble()).clamp(
+                0,
+                maxMs,
+              )
+            : 0,
+        max: maxMs,
+        onChangeStart: enabled ? _start : null,
+        onChanged: enabled ? _preview : null,
+        onChangeEnd: enabled ? _commit : null,
+      ),
     );
   }
 }