fix: Surface pen pressure, zoom glitches, sticky notes, selection UX

Wire Win32 pressure into Dart, tighten pinch guards, use geometric shape
strokes, expand the ink palette, and replace scratch-link split view with
an on-page sticky that shares the sidecar repo.

Co-authored-by: Cursor <cursoragent@cursor.com>

lib/editor/input/pen_input_service.dart

@@ -2,22 +2,9 @@
 //
 // Dart side of the native Windows pen observer (`windows/runner/pen_channel.cpp`).
 //
-// WHY THIS EXISTS: Flutter 3.44 on Windows delivers stylus PRESSURE but drops
-// the pen's barrel button, eraser/inverted end, and tilt (it does not map
-// POINTER_PEN_FLAG_* into `PointerEvent.buttons`/`invertedStylus`/`tilt`). The
-// native plugin observes WM_POINTER + GetPointerPenInfo and streams the missing
-// hardware state over an EventChannel; this service latches the LATEST value.
-//
-// CORRELATION (plan M2): we do NOT key state by Win32 pointerId joined to
-// Flutter's `event.pointer` — those are different id spaces. Only one pen is
-// active at a time, so a single latched "current" state is correct. The native
-// observer runs at the TOP of the window proc (BEFORE Flutter synthesizes its
-// pointer event, plan M1), so by the time Dart's pointer-down handler reads
-// [current], the latch already reflects that exact contact — no hover required.
-//
-// GRACEFUL DEGRADATION: on non-Windows (or if the channel is silent) the stream
-// simply never emits / errors are swallowed, and [current] stays [PenHardwareState.empty]
-// so the canvas falls back to its normal Flutter-pressure drawing.
+// Streams barrel / eraser / tilt / PRESSURE from WM_POINTER + GetPointerPenInfo.
+// Flutter's PointerEvent.pressure on Windows is unreliable (often flat); native
+// pressure (0..1024 → [0,1]) is preferred when [PenHardwareState.pressureValid].
 
 import 'dart:async';
 
@@ -35,22 +22,20 @@ class PenHardwareState {
     this.eraser = false,
     this.tiltX = 0.0,
     this.tiltY = 0.0,
+    this.pressure = 0.0,
+    this.pressureValid = false,
   });
 
-  /// Side barrel button held.
   final bool barrel;
-
-  /// Pen flipped to the inverted (eraser) end.
   final bool inverted;
-
-  /// Hardware eraser flag set.
   final bool eraser;
-
-  /// Tilt in degrees along X / Y ([-90, 90]); 0 = perpendicular.
   final double tiltX;
   final double tiltY;
 
-  /// Combined tilt magnitude in degrees (for [PenPoint.tilt]).
+  /// Normalized stylus pressure in [0,1] when [pressureValid] is true.
+  final double pressure;
+  final bool pressureValid;
+
   double get tiltMagnitude {
     final t = tiltX * tiltX + tiltY * tiltY;
     return t <= 0 ? 0.0 : _sqrt(t);
@@ -59,12 +44,10 @@ class PenHardwareState {
   static const empty = PenHardwareState();
 }
 
-// Avoids importing dart:math for a single call.
 double _sqrt(double v) {
   if (v <= 0) return 0;
   var x = v;
   var last = 0.0;
-  // Newton's method; converges fast for the small (<=~127) magnitudes here.
   for (var i = 0; i < 12 && x != last; i++) {
     last = x;
     x = 0.5 * (x + v / x);
@@ -72,33 +55,34 @@ double _sqrt(double v) {
   return x;
 }
 
-/// Latches the most recent [PenHardwareState] streamed by the native pen plugin.
-///
-/// Use the singleton [PenInputService.instance]. Call [start] once (e.g. in the
-/// editor's `initState`) and [stop] on dispose.
 class PenInputService {
   PenInputService._();
 
-  /// Process-wide singleton (one physical pen).
   static final PenInputService instance = PenInputService._();
 
-  /// Must match the native `EventChannel` name in `pen_channel.cpp`.
   static const EventChannel _channel = EventChannel('badnote/pen');
 
   StreamSubscription<dynamic>? _sub;
   PenHardwareState _current = PenHardwareState.empty;
 
-  /// The latest hardware pen state (or [PenHardwareState.empty] when no native
-  /// data has arrived — non-Windows, plugin absent, or channel silent).
   PenHardwareState get current => _current;
 
-  /// Whether the native channel has delivered at least one event (i.e. the
-  /// native pen plugin is present and active). Used to prefer hardware signals
-  /// over the Flutter fallback only when they are actually available.
   bool get isActive => _active;
   bool _active = false;
 
-  // Native-side diagnostics (see windows/runner/pen_channel.cpp).
+  final List<VoidCallback> _listeners = <VoidCallback>[];
+
+  /// Notify when native hardware state changes (barrel / pressure / tilt).
+  void addListener(VoidCallback listener) => _listeners.add(listener);
+
+  void removeListener(VoidCallback listener) => _listeners.remove(listener);
+
+  void _notifyListeners() {
+    for (final l in List<VoidCallback>.of(_listeners)) {
+      l();
+    }
+  }
+
   int _diagPtr = 0;
   int _diagPen = 0;
   int _diagMouse = 0;
@@ -108,47 +92,42 @@ class PenInputService {
   int _orPenMask = 0;
   int _btnChangeLast = 0;
   int _tiltAbsMax = 0;
+  double _pressureMaxSeen = 0;
 
   String _hex(int v) => '0x${v.toRadixString(16)}';
 
-  /// Multi-line native readout for the diagnostic overlay. The OR-accumulated
-  /// flag fields are the ground truth for which field carries the side/eraser
-  /// button: e.g. orPtrFlags with bit 0x20 (POINTER_FLAG_SECONDBUTTON) set means
-  /// the barrel button IS detectable.
   String get debugSummary => _active
       ? 'native ptr=$_diagPtr pen=$_diagPen mouse=$_diagMouse msg=${_hex(_diagMsg)}'
           '\n  orPtrFlags=${_hex(_orPtrFlags)} orPenFlags=${_hex(_orPenFlags)}'
           ' mask=${_hex(_orPenMask)} btnChg=$_btnChangeLast tiltMax=$_tiltAbsMax'
+          '\n  pressure=${_current.pressureValid ? _current.pressure.toStringAsFixed(3) : "n/a"}'
+          ' maxSeen=${_pressureMaxSeen.toStringAsFixed(3)}'
       : 'native: channel silent (no events)';
 
-  /// Begins listening to the native channel. Idempotent; safe on any platform
-  /// (no-ops where the channel has no handler).
   void start() {
     if (_sub != null) return;
     try {
       _sub = _channel.receiveBroadcastStream().listen(
         _onEvent,
-        onError: (Object _) {
-          // No native handler (e.g. Linux/macOS) or transient error — ignore
-          // and keep the empty fallback state.
-        },
+        onError: (Object _) {},
         cancelOnError: false,
       );
-    } catch (_) {
-      // receiveBroadcastStream can throw synchronously if the platform side is
-      // unavailable; degrade silently.
-    }
+    } catch (_) {}
   }
 
   void _onEvent(dynamic event) {
     if (event is! Map) return;
     final flags = (event['flags'] as num?)?.toInt() ?? 0;
+    final pressureValid = ((event['pressureValid'] as num?)?.toInt() ?? 0) != 0;
+    final pressure = (event['pressure'] as num?)?.toDouble() ?? 0.0;
     _current = PenHardwareState(
       barrel: flags & 0x1 != 0,
       inverted: flags & 0x2 != 0,
       eraser: flags & 0x4 != 0,
       tiltX: (event['tiltX'] as num?)?.toDouble() ?? 0.0,
       tiltY: (event['tiltY'] as num?)?.toDouble() ?? 0.0,
+      pressure: pressure.clamp(0.0, 1.0),
+      pressureValid: pressureValid,
     );
     _diagPtr = (event['diagPtr'] as num?)?.toInt() ?? _diagPtr;
     _diagPen = (event['diagPen'] as num?)?.toInt() ?? _diagPen;
@@ -159,16 +138,20 @@ class PenInputService {
     _orPenMask = (event['orPenMask'] as num?)?.toInt() ?? _orPenMask;
     _btnChangeLast = (event['btnChangeLast'] as num?)?.toInt() ?? _btnChangeLast;
     _tiltAbsMax = (event['tiltAbsMax'] as num?)?.toInt() ?? _tiltAbsMax;
+    _pressureMaxSeen =
+        (event['pressureMaxSeen'] as num?)?.toDouble() ?? _pressureMaxSeen;
+    if (pressureValid && pressure > _pressureMaxSeen) {
+      _pressureMaxSeen = pressure;
+    }
     _active = true;
 
-    // Log a PEN line whenever the raw per-event button/flag fields change, so
-    // the file captures exactly which field a button press sets (without
-    // flooding on every high-rate WM_POINTERUPDATE).
     final rawPtr = (event['rawPtrFlags'] as num?)?.toInt() ?? 0;
     final rawPen = (event['rawPenFlags'] as num?)?.toInt() ?? 0;
     final rawMask = (event['rawPenMask'] as num?)?.toInt() ?? 0;
     final btnChange = (event['btnChange'] as num?)?.toInt() ?? 0;
-    final key = '$rawPtr,$rawPen,$rawMask,$btnChange,${_current.tiltX},${_current.tiltY}';
+    final key =
+        '$rawPtr,$rawPen,$rawMask,$btnChange,${_current.tiltX},${_current.tiltY},'
+        '${pressureValid ? pressure.toStringAsFixed(2) : "x"}';
     if (key != _lastPenLogKey) {
       _lastPenLogKey = key;
       PenEventRing.instance.recordHardware(
@@ -188,7 +171,8 @@ class PenInputService {
           'btnChg': btnChange,
           'tiltX': _current.tiltX,
           'tiltY': _current.tiltY,
-          'resolved': '0x${flags.toRadixString(16)}',
+          'pressure': pressureValid ? pressure : null,
+          'pressureValid': pressureValid,
           'barrel': _current.barrel,
           'eraser': _current.eraser,
           'inverted': _current.inverted,
@@ -199,14 +183,15 @@ class PenInputService {
         'penFlags=0x${rawPen.toRadixString(16)} '
         'mask=0x${rawMask.toRadixString(16)} btnChg=$btnChange '
         'tilt=${_current.tiltX.toStringAsFixed(0)},${_current.tiltY.toStringAsFixed(0)} '
+        'p=${pressureValid ? pressure.toStringAsFixed(3) : "n/a"} '
         'msg=0x${_diagMsg.toRadixString(16)} resolved=0x${flags.toRadixString(16)}',
       );
     }
+    _notifyListeners();
   }
 
   String _lastPenLogKey = '';
 
-  /// Stops listening and resets state.
   void stop() {
     _sub?.cancel();
     _sub = null;