feat: select school terms and smooth refractive Dock motion

mobile/lib/widgets/glass_dock.dart

@@ -30,6 +30,14 @@ class _GlassDockState extends State<GlassDock> with TickerProviderStateMixin {
     value: 0,
   );
   bool _reduceMotion = false;
+  late int _targetIndex;
+  bool _elasticMotion = false;
+  @override
+  void initState() {
+    super.initState();
+    _targetIndex = widget.selectedIndex;
+  }
+
   double get _pressure => _press.value.clamp(0.0, 1.18);
   void _pressTo(double target) {
     if (_reduceMotion) {
@@ -38,7 +46,7 @@ class _GlassDockState extends State<GlassDock> with TickerProviderStateMixin {
     }
     _press.animateWith(
       SpringSimulation(
-        const SpringDescription(mass: 1, stiffness: 440, damping: 20),
+        const SpringDescription(mass: 1, stiffness: 440, damping: 17),
         _press.value,
         target,
         _press.velocity,
@@ -55,26 +63,36 @@ class _GlassDockState extends State<GlassDock> with TickerProviderStateMixin {
   double? _drag;
   double _dragSpeed = 0;
   double get _position => _drag ?? _motion.value.clamp(-0.12, 2.12);
-  void _spring(int index, [double velocity = 0]) {
+  void _moveTo(int index, {bool elastic = false, double velocity = 0}) {
+    _targetIndex = index;
+    _elasticMotion = elastic && !_reduceMotion;
     if (_reduceMotion) {
       _motion.value = index.toDouble();
       return;
     }
-    _motion.animateWith(
-      SpringSimulation(
-        const SpringDescription(mass: 1, stiffness: 380, damping: 23),
-        _position,
+    if (elastic) {
+      _motion.animateWith(
+        SpringSimulation(
+          const SpringDescription(mass: 1, stiffness: 380, damping: 19),
+          _position,
+          index.toDouble(),
+          velocity.clamp(-8, 8),
+        ),
+      );
+    } else {
+      _motion.animateTo(
         index.toDouble(),
-        velocity.clamp(-8, 8),
-      ),
-    );
+        duration: const Duration(milliseconds: 320),
+        curve: Curves.easeOutCubic,
+      );
+    }
   }
 
-  void _select(int index, [double velocity = 0]) {
+  void _select(int index, {bool elastic = false, double velocity = 0}) {
     final position = _position;
     setState(() => _drag = null);
     _motion.value = position;
-    _spring(index, velocity);
+    _moveTo(index, elastic: elastic, velocity: velocity);
     _pressTo(0);
     widget.onSelected(index);
   }
@@ -82,8 +100,10 @@ class _GlassDockState extends State<GlassDock> with TickerProviderStateMixin {
   @override
   void didUpdateWidget(GlassDock oldWidget) {
     super.didUpdateWidget(oldWidget);
-    if (oldWidget.selectedIndex != widget.selectedIndex && _drag == null) {
-      _spring(widget.selectedIndex);
+    // The parent acknowledges onSelected with a rebuild. Restarting here used
+    // to erase the release velocity and start a second spring for the same tab.
+    if (widget.selectedIndex != _targetIndex && _drag == null) {
+      _moveTo(widget.selectedIndex);
     }
   }
 
@@ -124,12 +144,10 @@ class _GlassDockState extends State<GlassDock> with TickerProviderStateMixin {
     );
     return ClipRRect(
       borderRadius: BorderRadius.circular(40),
-      child: lens
-          ? GlassRefraction(strength: 0.25 + pressure * 0.95, child: content)
-          : BackdropFilter(
-              filter: ui.ImageFilter.blur(sigmaX: 1.0, sigmaY: 1.0),
-              child: content,
-            ),
+      child: GlassRefraction(
+        strength: lens ? 0.25 + pressure * 0.95 : 0.32,
+        child: content,
+      ),
     );
   }
 
@@ -138,12 +156,19 @@ class _GlassDockState extends State<GlassDock> with TickerProviderStateMixin {
     animation: Listenable.merge([_motion, _press]),
     builder: (context, _) {
       final press = _pressure;
-      final speed = (_drag != null ? _dragSpeed : _motion.velocity).abs();
-      final stretch = (speed / 16).clamp(0.0, 0.12) + press * 0.18;
+      final speed = _reduceMotion
+          ? 0.0
+          : (_drag != null
+                    ? _dragSpeed
+                    : _elasticMotion
+                    ? _motion.velocity
+                    : 0.0)
+                .abs();
+      final stretch = (speed / 16).clamp(0.0, 0.14) + press * 0.30;
       final lensWidth = _travel * (1 + stretch);
       final lensHeight =
           (_height - _inset * 2) *
-          (1 + press * 0.19 - (speed / 16).clamp(0.0, 0.07));
+          (1 + press * 0.31 - (speed / 16).clamp(0.0, 0.07));
       return SizedBox(
         width: _width,
         height: _height,
@@ -201,7 +226,7 @@ class _GlassDockState extends State<GlassDock> with TickerProviderStateMixin {
       child: GestureDetector(
         key: index == widget.selectedIndex ? const Key('dock-cursor') : null,
         behavior: HitTestBehavior.opaque,
-        onTapDown: (_) => _pressTo(1),
+        onTapDown: index == widget.selectedIndex ? (_) => _pressTo(1) : null,
         onTapCancel: () {
           if (_drag == null) _pressTo(0);
         },
@@ -229,7 +254,8 @@ class _GlassDockState extends State<GlassDock> with TickerProviderStateMixin {
         onHorizontalDragEnd: index == widget.selectedIndex
             ? (details) => _select(
                 _position.round().clamp(0, 2),
-                details.velocity.pixelsPerSecond.dx / _travel,
+                elastic: true,
+                velocity: details.velocity.pixelsPerSecond.dx / _travel,
               )
             : null,
         onHorizontalDragCancel: index == widget.selectedIndex
@@ -238,7 +264,7 @@ class _GlassDockState extends State<GlassDock> with TickerProviderStateMixin {
                 final position = _position;
                 setState(() => _drag = null);
                 _motion.value = position;
-                _spring(widget.selectedIndex);
+                _moveTo(widget.selectedIndex, elastic: true);
                 _pressTo(0);
               }
             : null,