Revert clamping scroll simulation changes (#89885)

dev/tools/generate_android_spline_data.dart

-// Copyright 2014 The Flutter Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-const int _nbSamples = 100;
-final List<double> _splinePosition = List<double>.filled(_nbSamples + 1, 0.0);
-final List<double> _splineTime = List<double>.filled(_nbSamples + 1, 0.0);
-const double _startTension = 0.5;
-const double _endTension = 1.0;
-const double _inflexion = 0.35;
-
-// Generate the spline data used in ClampingScrollSimulation.
-//
-// This logic is a translation of the 2-dimensional logic found in
-// https://android.googlesource.com/platform/frameworks/base/+/master/core/java/android/widget/Scroller.java.
-//
-// The output of this program should be copied over to [_splinePosition] in
-// flutter/packages/flutter/lib/src/widgets/scroll_simulation.dart.
-void main() {
-  const double p1 = _startTension * _inflexion;
-  const double p2 = 1.0 - _endTension * (1.0 - _inflexion);
-  double xMin = 0.0;
-  double yMin = 0.0;
-  for (int i = 0; i < _nbSamples; i++) {
-    final double alpha = i / _nbSamples;
-    double xMax = 1.0;
-    double x, tx, coef;
-    while (true) {
-      x = xMin + (xMax - xMin) / 2.0;
-      coef = 3.0 * x * (1.0 - x);
-      tx = coef * ((1.0 - x) * p1 + x * p2) + x * x * x;
-      if ((tx - alpha).abs() < 1e-5) {
-        break;
-      }
-      if (tx > alpha) {
-        xMax = x;
-      } else {
-        xMin = x;
-      }
-    }
-    _splinePosition[i] = coef * ((1.0 - x) * _startTension + x) + x * x * x;
-    double yMax = 1.0;
-    double y, dy;
-    while (true) {
-      y = yMin + (yMax - yMin) / 2.0;
-      coef = 3.0 * y * (1.0 - y);
-      dy = coef * ((1.0 - y) * _startTension + y) + y * y * y;
-      if ((dy - alpha).abs() < 1e-5) {
-        break;
-      }
-      if (dy > alpha) {
-        yMax = y;
-      } else {
-        yMin = y;
-      }
-    }
-    _splineTime[i] = coef * ((1.0 - y) * p1 + y * p2) + y * y * y;
-  }
-  _splinePosition[_nbSamples] = _splineTime[_nbSamples] = 1.0;
-  print(_splinePosition);
-}

packages/flutter/lib/src/widgets/scroll_simulation.dart

@@ -129,8 +129,6 @@ class BouncingScrollSimulation extends Simulation {
   }
 }
 
-const double _inflexion = 0.35;
-
 /// An implementation of scroll physics that matches Android.
 ///
 /// See also:
@@ -149,9 +147,10 @@ class ClampingScrollSimulation extends Simulation {
     required this.velocity,
     this.friction = 0.015,
     Tolerance tolerance = Tolerance.defaultTolerance,
-  }) : super(tolerance: tolerance) {
-    _duration = _splineFlingDuration(velocity);
-    _distance = _splineFlingDistance(velocity);
+  }) : assert(_flingVelocityPenetration(0.0) == _initialVelocityPenetration),
+       super(tolerance: tolerance) {
+    _duration = _flingDuration(velocity);
+    _distance = (velocity * _duration / _initialVelocityPenetration).abs();
   }
 
   /// The position of the particle at the beginning of the simulation.
@@ -166,7 +165,7 @@ class ClampingScrollSimulation extends Simulation {
   /// The more friction the particle experiences, the sooner it stops.
   final double friction;
 
-  late int _duration;
+  late double _duration;
   late double _distance;
 
   // See DECELERATION_RATE.
@@ -174,184 +173,59 @@ class ClampingScrollSimulation extends Simulation {
 
   // See computeDeceleration().
   static double _decelerationForFriction(double friction) {
-    return 9.80665 *
-        39.37 *
-        friction *
-        1.0 * // Flutter operates on logical pixels so the DPI should be 1.0.
-        160.0;
+    return friction * 61774.04968;
   }
 
-  // See getSplineDeceleration().
-  double _splineDeceleration(double velocity) {
-    return math.log(_inflexion * velocity.abs() / (friction * _decelerationForFriction(0.84)));
+  // See getSplineFlingDuration(). Returns a value in seconds.
+  double _flingDuration(double velocity) {
+    // See mPhysicalCoeff
+    final double scaledFriction = friction * _decelerationForFriction(0.84);
+
+    // See getSplineDeceleration().
+    final double deceleration = math.log(0.35 * velocity.abs() / scaledFriction);
+
+    return math.exp(deceleration / (_kDecelerationRate - 1.0));
   }
 
-  // See getSplineFlingDuration().
-  int _splineFlingDuration(double velocity) {
-    final double deceleration = _splineDeceleration(velocity);
-    return (1000 * math.exp(deceleration / (_kDecelerationRate - 1.0))).round();
+  // Based on a cubic curve fit to the Scroller.computeScrollOffset() values
+  // produced for an initial velocity of 4000. The value of Scroller.getDuration()
+  // and Scroller.getFinalY() were 686ms and 961 pixels respectively.
+  //
+  // Algebra courtesy of Wolfram Alpha.
+  //
+  // f(x) = scrollOffset, x is time in milliseconds
+  // f(x) = 3.60882×10^-6 x^3 - 0.00668009 x^2 + 4.29427 x - 3.15307
+  // f(x) = 3.60882×10^-6 x^3 - 0.00668009 x^2 + 4.29427 x, so f(0) is 0
+  // f(686ms) = 961 pixels
+  // Scale to f(0 <= t <= 1.0), x = t * 686
+  // f(t) = 1165.03 t^3 - 3143.62 t^2 + 2945.87 t
+  // Scale f(t) so that 0.0 <= f(t) <= 1.0
+  // f(t) = (1165.03 t^3 - 3143.62 t^2 + 2945.87 t) / 961.0
+  //      = 1.2 t^3 - 3.27 t^2 + 3.065 t
+  static const double _initialVelocityPenetration = 3.065;
+  static double _flingDistancePenetration(double t) {
+    return (1.2 * t * t * t) - (3.27 * t * t) + (_initialVelocityPenetration * t);
   }
 
-  // See getSplineFlingDistance().
-  double _splineFlingDistance(double velocity) {
-    final double l = _splineDeceleration(velocity);
-    final double decelMinusOne = _kDecelerationRate - 1.0;
-    return friction *
-        _decelerationForFriction(0.84) *
-        math.exp(_kDecelerationRate / decelMinusOne * l);
+  // The derivative of the _flingDistancePenetration() function.
+  static double _flingVelocityPenetration(double t) {
+    return (3.6 * t * t) - (6.54 * t) + _initialVelocityPenetration;
   }
 
   @override
   double x(double time) {
-    if (time == 0) {
-      return position;
-    }
-    final _NBSample sample = _NBSample(time, _duration);
-    return position + (sample.distanceCoef * _distance) * velocity.sign;
+    final double t = (time / _duration).clamp(0.0, 1.0);
+    return position + _distance * _flingDistancePenetration(t) * velocity.sign;
   }
 
   @override
   double dx(double time) {
-    if (time == 0) {
-      return velocity;
-    }
-    final _NBSample sample = _NBSample(time, _duration);
-    return sample.velocityCoef * _distance / _duration * velocity.sign * 1000.0;
+    final double t = (time / _duration).clamp(0.0, 1.0);
+    return _distance * _flingVelocityPenetration(t) * velocity.sign / _duration;
   }
 
   @override
   bool isDone(double time) {
-    return time * 1000.0 >= _duration;
-  }
-}
-
-class _NBSample {
-  _NBSample(double time, int duration) {
-    // See computeScrollOffset().
-    final double t = time * 1000.0 / duration;
-    final int index = (_nbSamples * t).clamp(0, _nbSamples).round();
-    _distanceCoef = 1.0;
-    _velocityCoef = 0.0;
-    if (index < _nbSamples) {
-      final double tInf = index / _nbSamples;
-      final double tSup = (index + 1) / _nbSamples;
-      final double dInf = _splinePosition[index];
-      final double dSup = _splinePosition[index + 1];
-      _velocityCoef = (dSup - dInf) / (tSup - tInf);
-      _distanceCoef = dInf + (t - tInf) * _velocityCoef;
-    }
+    return time >= _duration;
   }
-
-  late double _velocityCoef;
-  double get velocityCoef => _velocityCoef;
-
-  late double _distanceCoef;
-  double get distanceCoef => _distanceCoef;
-
-  static const int _nbSamples = 100;
-
-  // Generated from dev/tools/generate_android_spline_data.dart.
-  static final List<double> _splinePosition = <double>[
-    0.000022888183591973643,
-    0.028561000304762274,
-    0.05705195792956655,
-    0.08538917797618413,
-    0.11349556286812107,
-    0.14129881694635613,
-    0.16877157254923383,
-    0.19581093511175632,
-    0.22239649722992452,
-    0.24843841866631658,
-    0.2740024733220569,
-    0.298967680744136,
-    0.32333234658228116,
-    0.34709556909569184,
-    0.3702249257894571,
-    0.39272483400399893,
-    0.41456988647721615,
-    0.43582889025419114,
-    0.4564192786416,
-    0.476410299013587,
-    0.4957560715637827,
-    0.5145493169954743,
-    0.5327205670880077,
-    0.5502846891191615,
-    0.5673274324802855,
-    0.583810881323224,
-    0.5997478744397482,
-    0.615194045299478,
-    0.6301165005270208,
-    0.6445484042257972,
-    0.6585198219185201,
-    0.6720397744233084,
-    0.6850997688076114,
-    0.6977281404741683,
-    0.7099506591298411,
-    0.7217749311525871,
-    0.7331784038850426,
-    0.7442308394229518,
-    0.7549087205105974,
-    0.7652471277371271,
-    0.7752251637549381,
-    0.7848768260203478,
-    0.7942056937103814,
-    0.8032299679689082,
-    0.8119428702388629,
-    0.8203713516576219,
-    0.8285187880808974,
-    0.8363794492831295,
-    0.8439768562813565,
-    0.851322799855549,
-    0.8584111051351724,
-    0.8652534074722162,
-    0.8718525580962131,
-    0.8782333271742155,
-    0.8843892099362031,
-    0.8903155590440985,
-    0.8960465359221951,
-    0.9015574505919048,
-    0.9068736766459904,
-    0.9119951682409297,
-    0.9169321898723632,
-    0.9216747065581234,
-    0.9262420604674766,
-    0.9306331858366086,
-    0.9348476990715433,
-    0.9389007110754832,
-    0.9427903495057521,
-    0.9465220679845756,
-    0.9500943036519721,
-    0.9535176728088761,
-    0.9567898524767604,
-    0.959924306623116,
-    0.9629127700159108,
-    0.9657622101750765,
-    0.9684818726275105,
-    0.9710676079044347,
-    0.9735231939498,
-    0.9758514437576309,
-    0.9780599066560445,
-    0.9801485715370128,
-    0.9821149805689633,
-    0.9839677526782791,
-    0.9857085499421516,
-    0.9873347811966005,
-    0.9888547171706613,
-    0.9902689443512227,
-    0.9915771042095881,
-    0.9927840651641069,
-    0.9938913963715834,
-    0.9948987305580712,
-    0.9958114963810524,
-    0.9966274782266875,
-    0.997352148697352,
-    0.9979848677523623,
-    0.9985285021374979,
-    0.9989844084453229,
-    0.9993537595844986,
-    0.999638729860106,
-    0.9998403888004533,
-    0.9999602810470701,
-    1.0,
-  ];
 }

packages/flutter/test/widgets/list_wheel_scroll_view_test.dart

@@ -1236,7 +1236,7 @@ void main() {
       await tester.fling(
         find.byType(ListWheelScrollView),
         const Offset(0.0, -50.0),
-        100.0,
+        800.0,
       );
 
       // At this moment, the ballistics is started but 50px is still inside the

packages/flutter/test/widgets/scroll_simulation_test.dart

@@ -23,21 +23,4 @@ void main() {
     checkInitialConditions(75.0, 614.2093);
     checkInitialConditions(5469.0, 182.114534);
   });
-
-  test('ClampingScrollSimulation velocity eventually reaches zero', () {
-    void checkFinalConditions(double position, double velocity) {
-      final ClampingScrollSimulation simulation = ClampingScrollSimulation(position: position, velocity: velocity);
-      expect(simulation.dx(10.0), equals(0.0));
-    }
-
-    checkFinalConditions(51.0, 2000.0);
-    checkFinalConditions(584.0, 2617.294734);
-    checkFinalConditions(345.0, 1982.785934);
-    checkFinalConditions(0.0, 1831.366634);
-    checkFinalConditions(-156.2, 1541.57665);
-    checkFinalConditions(4.0, 1139.250439);
-    checkFinalConditions(4534.0, 1073.553798);
-    checkFinalConditions(75.0, 614.2093);
-    checkFinalConditions(5469.0, 182.114534);
-  });
 }

packages/flutter/test/widgets/scrollable_fling_test.dart

@@ -44,6 +44,11 @@ void main() {
     expect(getCurrentOffset(), dragOffset);
     await tester.pump(const Duration(seconds: 5));
     final double androidResult = getCurrentOffset();
+    // Regression test for https://github.com/flutter/flutter/issues/83632
+    // Before changing these values, ensure the fling results in a distance that
+    // makes sense. See issue for more context.
+    expect(androidResult, greaterThan(394.0));
+    expect(androidResult, lessThan(395.0));
 
     await pumpTest(tester, TargetPlatform.linux);
     await tester.fling(find.byType(ListView), const Offset(0.0, -dragOffset), 1000.0);
@@ -147,6 +152,6 @@ void main() {
     expect(log, equals(<String>['tap 21']));
     await tester.tap(find.byType(Scrollable));
     await tester.pump(const Duration(milliseconds: 50));
-    expect(log, equals(<String>['tap 21', 'tap 49']));
+    expect(log, equals(<String>['tap 21', 'tap 48']));
   });
 }

packages/flutter/test/widgets/scrollable_semantics_test.dart

@@ -233,7 +233,7 @@ void main() {
 
     expect(semantics, includesNodeWith(
       scrollExtentMin: 0.0,
-      scrollPosition: 394.3,
+      scrollPosition: 380.2,
       scrollExtentMax: 520.0,
       actions: <SemanticsAction>[
         SemanticsAction.scrollUp,
@@ -282,7 +282,7 @@ void main() {
 
     expect(semantics, includesNodeWith(
       scrollExtentMin: 0.0,
-      scrollPosition: 394.3,
+      scrollPosition: 380.2,
       scrollExtentMax: double.infinity,
       actions: <SemanticsAction>[
         SemanticsAction.scrollUp,
@@ -294,7 +294,7 @@ void main() {
 
     expect(semantics, includesNodeWith(
       scrollExtentMin: 0.0,
-      scrollPosition: 788.6,
+      scrollPosition: 760.4,
       scrollExtentMax: double.infinity,
       actions: <SemanticsAction>[
         SemanticsAction.scrollUp,

packages/flutter/test/widgets/scrollable_test.dart

@@ -918,8 +918,8 @@ void main() {
     expect(find.byKey(const ValueKey<String>('Box 0')), findsNothing);
     expect(find.byKey(const ValueKey<String>('Box 52')), findsOneWidget);
 
-    expect(expensiveWidgets, 40);
-    expect(cheapWidgets, 21);
+    expect(expensiveWidgets, 38);
+    expect(cheapWidgets, 20);
   });
 
   testWidgets('Can recommendDeferredLoadingForContext - override heuristic', (WidgetTester tester) async {
@@ -961,9 +961,9 @@ void main() {
     expect(find.byKey(const ValueKey<String>('Box 0')), findsNothing);
     expect(find.byKey(const ValueKey<String>('Cheap box 52')), findsOneWidget);
 
-    expect(expensiveWidgets, 17);
-    expect(cheapWidgets, 44);
-    expect(physics.count, 44 + 17);
+    expect(expensiveWidgets, 18);
+    expect(cheapWidgets, 40);
+    expect(physics.count, 40 + 18);
   });
 
   testWidgets('Can recommendDeferredLoadingForContext - override heuristic and always return true', (WidgetTester tester) async {
@@ -1004,7 +1004,7 @@ void main() {
     expect(find.byKey(const ValueKey<String>('Cheap box 52')), findsOneWidget);
 
     expect(expensiveWidgets, 0);
-    expect(cheapWidgets, 61);
+    expect(cheapWidgets, 58);
   });
 
   testWidgets('ensureVisible does not move PageViews', (WidgetTester tester) async {

packages/flutter/test/widgets/slivers_appbar_floating_pinned_test.dart

@@ -151,7 +151,7 @@ void main() {
     );
     expect(semantics, hasSemantics(expectedSemantics, ignoreTransform: true, ignoreId: true, ignoreRect: true));
 
-    await tester.fling(find.text('Tile 2'), const Offset(0, -600), 1950);
+    await tester.fling(find.text('Tile 2'), const Offset(0, -600), 2000);
     await tester.pumpAndSettle();
 
     expectedSemantics = TestSemantics.root(