fix: PDF finger ink, chrome UX, OneNote pens, and pen physics

Wire finger drawing on PDF without breaking pinch; auto-hide page scrubber and fix bounce; share sticky tools with resize and per-page remember; side-button select; separate pen slots with colors; rnote pressure shapes plus tip-velocity width and lower stroke latency.

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

lib/editor/canvas/pen_canvas.dart

@@ -22,6 +22,7 @@ import 'package:flutter/gestures.dart';
 import 'package:flutter/material.dart';
 
 import '../engine/brush.dart';
+import '../engine/pen_physics.dart';
 import '../engine/stroke_eraser.dart';
 import '../engine/stroke_geometry.dart' show kDefaultPenThinning;
 import '../engine/stroke_model.dart';
@@ -33,6 +34,7 @@ import '../input/pressure_curve.dart';
 import '../input/pen_input_service.dart';
 import '../../diagnostics/pen_event_ring.dart';
 import '../engine/shape_geometry.dart';
+import 'dart:math' as math;
 import '../render/ink_picture_cache.dart';
 import '../render/live_ink_painter.dart' as render;
 import '../render/static_ink_painter.dart' as render;
@@ -230,6 +232,10 @@ class _PenCanvasState extends State<PenCanvas> {
   /// undo snapshot is recorded once, on the first drag delta — see _extendStroke).
   bool _selectDragging = false;
 
+  /// Tip-velocity tracker for [tipVelocityWidthScale] (physical ink starvation).
+  Offset? _lastTipNorm;
+  Duration? _lastTipTime;
+
   /// True when the active stylus reports the eraser signal (barrel button or
   /// inverted stylus), detected on hover/down.
   bool _eraserActive = false;
@@ -399,7 +405,8 @@ class _PenCanvasState extends State<PenCanvas> {
     if (action == _lastHwAction) return;
     _lastHwAction = action;
     if (action == PenButtonAction.undo ||
-        action == PenButtonAction.toggleTool) {
+        action == PenButtonAction.toggleTool ||
+        action == PenButtonAction.select) {
       widget.onPenButtonAction?.call(action);
     }
   }
@@ -441,7 +448,7 @@ class _PenCanvasState extends State<PenCanvas> {
   /// Map a global pointer position into normalized page coords using the
   /// shared transform (inverse) and this widget's geometry.
   PenPoint? _toNormalized(Offset globalPosition, double? pressure,
-      {double? tilt}) {
+      {double? tilt, Duration? timeStamp}) {
     final box = context.findRenderObject() as RenderBox?;
     if (box == null) return null;
     final local = box.globalToLocal(globalPosition);
@@ -451,7 +458,23 @@ class _PenCanvasState extends State<PenCanvas> {
 
     final nx = scene.dx / widget.pageSize.width;
     final ny = scene.dy / widget.pageSize.height;
-    return PenPoint(nx, ny, pressure, tilt: tilt);
+
+    double? shaped = pressure;
+    if (shaped != null && timeStamp != null && _lastTipNorm != null &&
+        _lastTipTime != null) {
+      final dt = (timeStamp - _lastTipTime!).inMicroseconds / 1e6;
+      if (dt > 0) {
+        final dx = nx - _lastTipNorm!.dx;
+        final dy = ny - _lastTipNorm!.dy;
+        final speed = math.sqrt(dx * dx + dy * dy) / dt;
+        shaped = (shaped * tipVelocityWidthScale(_currentBrush, speed))
+            .clamp(0.0, 1.0);
+      }
+    }
+    _lastTipNorm = Offset(nx, ny);
+    _lastTipTime = timeStamp;
+
+    return PenPoint(nx, ny, shaped, tilt: tilt);
   }
 
   // --- Stroke lifecycle -----------------------------------------------------
@@ -464,8 +487,10 @@ class _PenCanvasState extends State<PenCanvas> {
     _shapeStart = null;
     _selectLast = null;
     _selectDragging = false;
+    _lastTipNorm = null;
+    _lastTipTime = null;
     final p = _toNormalized(event.position, _normalizedPressure(event),
-        tilt: _tiltFor(event));
+        tilt: _tiltFor(event), timeStamp: event.timeStamp);
 
     if (_eraserActive || widget.tool == CanvasTool.eraser) {
       _eraserCursor.value = p;
@@ -502,7 +527,7 @@ class _PenCanvasState extends State<PenCanvas> {
 
   void _extendStroke(PointerMoveEvent event) {
     final p = _toNormalized(event.position, _normalizedPressure(event),
-        tilt: _tiltFor(event));
+        tilt: _tiltFor(event), timeStamp: event.timeStamp);
     if (p == null) return;
 
     if (_eraserActive || widget.tool == CanvasTool.eraser) {