Disable cursor opacity animation on macOS, make iOS cursor animation discrete (flutter#104335)

Author: LongCatIsLooong

packages/flutter/lib/src/material/text_field.dart

@@ -1168,7 +1168,7 @@ class _TextFieldState extends State<TextField> with RestorationMixin implements
         forcePressEnabled = false;
         textSelectionControls ??= cupertinoDesktopTextSelectionControls;
         paintCursorAboveText = true;
-        cursorOpacityAnimates = true;
+        cursorOpacityAnimates = false;
         cursorColor = widget.cursorColor ?? selectionStyle.cursorColor ?? cupertinoTheme.primaryColor;
         selectionColor = selectionStyle.selectionColor ?? cupertinoTheme.primaryColor.withOpacity(0.40);
         cursorRadius ??= const Radius.circular(2.0);

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

@@ -52,10 +52,6 @@ typedef AppPrivateCommandCallback = void Function(String, Map<String, dynamic>);
 // to transparent, is twice this duration.
 const Duration _kCursorBlinkHalfPeriod = Duration(milliseconds: 500);
 
-// The time the cursor is static in opacity before animating to become
-// transparent.
-const Duration _kCursorBlinkWaitForStart = Duration(milliseconds: 150);
-
 // Number of cursor ticks during which the most recently entered character
 // is shown in an obscured text field.
 const int _kObscureShowLatestCharCursorTicks = 3;
@@ -301,6 +297,91 @@ class ToolbarOptions {
   final bool selectAll;
 }
 
+// A time-value pair that represents a key frame in an animation.
+class _KeyFrame {
+  const _KeyFrame(this.time, this.value);
+  // Values extracted from iOS 15.4 UIKit.
+  static const List<_KeyFrame> iOSBlinkingCaretKeyFrames = <_KeyFrame>[
+    _KeyFrame(0,       1),     // 0
+    _KeyFrame(0.5,     1),     // 1
+    _KeyFrame(0.5375,  0.75),  // 2
+    _KeyFrame(0.575,   0.5),   // 3
+    _KeyFrame(0.6125,  0.25),  // 4
+    _KeyFrame(0.65,    0),     // 5
+    _KeyFrame(0.85,    0),     // 6
+    _KeyFrame(0.8875,  0.25),  // 7
+    _KeyFrame(0.925,   0.5),   // 8
+    _KeyFrame(0.9625,  0.75),  // 9
+    _KeyFrame(1,       1),     // 10
+  ];
+
+  // The timing, in seconds, of the specified animation `value`.
+  final double time;
+  final double value;
+}
+
+class _DiscreteKeyFrameSimulation extends Simulation {
+  _DiscreteKeyFrameSimulation.iOSBlinkingCaret() : this._(_KeyFrame.iOSBlinkingCaretKeyFrames, 1);
+  _DiscreteKeyFrameSimulation._(this._keyFrames, this.maxDuration)
+    : assert(_keyFrames.isNotEmpty),
+      assert(_keyFrames.last.time <= maxDuration),
+      assert(() {
+        for (int i = 0; i < _keyFrames.length -1; i += 1) {
+          if (_keyFrames[i].time > _keyFrames[i + 1].time) {
+            return false;
+          }
+        }
+        return true;
+      }(), 'The key frame sequence must be sorted by time.');
+
+  final double maxDuration;
+
+  final List<_KeyFrame> _keyFrames;
+
+  @override
+  double dx(double time) => 0;
+
+  @override
+  bool isDone(double time) => time >= maxDuration;
+
+  // The index of the KeyFrame corresponds to the most recent input `time`.
+  int _lastKeyFrameIndex = 0;
+
+  @override
+  double x(double time) {
+    final int length = _keyFrames.length;
+
+    // Perform a linear search in the sorted key frame list, starting from the
+    // last key frame found, since the input `time` usually monotonically
+    // increases by a small amount.
+    int searchIndex;
+    final int endIndex;
+    if (_keyFrames[_lastKeyFrameIndex].time > time) {
+      // The simulation may have restarted. Search within the index range
+      // [0, _lastKeyFrameIndex).
+      searchIndex = 0;
+      endIndex = _lastKeyFrameIndex;
+    } else {
+      searchIndex = _lastKeyFrameIndex;
+      endIndex = length;
+    }
+
+    // Find the target key frame. Don't have to check (endIndex - 1): if
+    // (endIndex - 2) doesn't work we'll have to pick (endIndex - 1) anyways.
+    while (searchIndex < endIndex - 1) {
+      assert(_keyFrames[searchIndex].time <= time);
+      final _KeyFrame next = _keyFrames[searchIndex + 1];
+      if (time < next.time) {
+        break;
+      }
+      searchIndex += 1;
+    }
+
+    _lastKeyFrameIndex = searchIndex;
+    return _keyFrames[_lastKeyFrameIndex].value;
+  }
+}
+
 /// A basic text input field.
 ///
 /// This widget interacts with the [TextInput] service to let the user edit the
@@ -1597,7 +1678,14 @@ class EditableText extends StatefulWidget {
 /// State for a [EditableText].
 class EditableTextState extends State<EditableText> with AutomaticKeepAliveClientMixin<EditableText>, WidgetsBindingObserver, TickerProviderStateMixin<EditableText>, TextSelectionDelegate implements TextInputClient, AutofillClient {
   Timer? _cursorTimer;
-  bool _targetCursorVisibility = false;
+  AnimationController get _cursorBlinkOpacityController {
+    return _backingCursorBlinkOpacityController ??= AnimationController(
+      vsync: this,
+    )..addListener(_onCursorColorTick);
+  }
+  AnimationController? _backingCursorBlinkOpacityController;
+  late final Simulation _iosBlinkCursorSimulation = _DiscreteKeyFrameSimulation.iOSBlinkingCaret();
+
   final ValueNotifier<bool> _cursorVisibilityNotifier = ValueNotifier<bool>(true);
   final GlobalKey _editableKey = GlobalKey();
   final ClipboardStatusNotifier? _clipboardStatus = kIsWeb ? null : ClipboardStatusNotifier();
@@ -1608,8 +1696,6 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
   ScrollController? _internalScrollController;
   ScrollController get _scrollController => widget.scrollController ?? (_internalScrollController ??= ScrollController());
 
-  AnimationController? _cursorBlinkOpacityController;
-
   final LayerLink _toolbarLayerLink = LayerLink();
   final LayerLink _startHandleLayerLink = LayerLink();
   final LayerLink _endHandleLayerLink = LayerLink();
@@ -1637,10 +1723,6 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
   /// - Changing the selection using a physical keyboard.
   bool get _shouldCreateInputConnection => kIsWeb || !widget.readOnly;
 
-  // This value is an eyeball estimation of the time it takes for the iOS cursor
-  // to ease in and out.
-  static const Duration _fadeDuration = Duration(milliseconds: 250);
-
   // The time it takes for the floating cursor to snap to the text aligned
   // cursor position after the user has finished placing it.
   static const Duration _floatingCursorResetTime = Duration(milliseconds: 125);
@@ -1652,7 +1734,7 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
   @override
   bool get wantKeepAlive => widget.focusNode.hasFocus;
 
-  Color get _cursorColor => widget.cursorColor.withOpacity(_cursorBlinkOpacityController!.value);
+  Color get _cursorColor => widget.cursorColor.withOpacity(_cursorBlinkOpacityController.value);
 
   @override
   bool get cutEnabled => widget.toolbarOptions.cut && !widget.readOnly && !widget.obscureText;
@@ -1806,10 +1888,6 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
   @override
   void initState() {
     super.initState();
-    _cursorBlinkOpacityController = AnimationController(
-      vsync: this,
-      duration: _fadeDuration,
-    )..addListener(_onCursorColorTick);
     _clipboardStatus?.addListener(_onChangedClipboardStatus);
     widget.controller.addListener(_didChangeTextEditingValue);
     widget.focusNode.addListener(_handleFocusChanged);
@@ -1846,7 +1924,7 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
     if (_tickersEnabled != newTickerEnabled) {
       _tickersEnabled = newTickerEnabled;
       if (_tickersEnabled && _cursorActive) {
-        _startCursorTimer();
+        _startCursorBlink();
       } else if (!_tickersEnabled && _cursorTimer != null) {
         // Cannot use _stopCursorTimer because it would reset _cursorActive.
         _cursorTimer!.cancel();
@@ -1946,8 +2024,8 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
     assert(!_hasInputConnection);
     _cursorTimer?.cancel();
     _cursorTimer = null;
-    _cursorBlinkOpacityController?.dispose();
-    _cursorBlinkOpacityController = null;
+    _backingCursorBlinkOpacityController?.dispose();
+    _backingCursorBlinkOpacityController = null;
     _selectionOverlay?.dispose();
     _selectionOverlay = null;
     widget.focusNode.removeListener(_handleFocusChanged);
@@ -2026,8 +2104,8 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
     if (_hasInputConnection) {
       // To keep the cursor from blinking while typing, we want to restart the
       // cursor timer every time a new character is typed.
-      _stopCursorTimer(resetCharTicks: false);
-      _startCursorTimer();
+      _stopCursorBlink(resetCharTicks: false);
+      _startCursorBlink();
     }
   }
 
@@ -2548,8 +2626,8 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
 
     // To keep the cursor from blinking while it moves, restart the timer here.
     if (_cursorTimer != null) {
-      _stopCursorTimer(resetCharTicks: false);
-      _startCursorTimer();
+      _stopCursorBlink(resetCharTicks: false);
+      _startCursorBlink();
     }
   }
 
@@ -2703,14 +2781,14 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
   }
 
   void _onCursorColorTick() {
-    renderEditable.cursorColor = widget.cursorColor.withOpacity(_cursorBlinkOpacityController!.value);
-    _cursorVisibilityNotifier.value = widget.showCursor && _cursorBlinkOpacityController!.value > 0;
+    renderEditable.cursorColor = widget.cursorColor.withOpacity(_cursorBlinkOpacityController.value);
+    _cursorVisibilityNotifier.value = widget.showCursor && _cursorBlinkOpacityController.value > 0;
   }
 
   /// Whether the blinking cursor is actually visible at this precise moment
   /// (it's hidden half the time, since it blinks).
   @visibleForTesting
-  bool get cursorCurrentlyVisible => _cursorBlinkOpacityController!.value > 0;
+  bool get cursorCurrentlyVisible => _cursorBlinkOpacityController.value > 0;
 
   /// The cursor blink interval (the amount of time the cursor is in the "on"
   /// state or the "off" state). A complete cursor blink period is twice this
@@ -2725,83 +2803,69 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
   int _obscureShowCharTicksPending = 0;
   int? _obscureLatestCharIndex;
 
-  void _cursorTick(Timer timer) {
-    _targetCursorVisibility = !_targetCursorVisibility;
-    final double targetOpacity = _targetCursorVisibility ? 1.0 : 0.0;
-    if (widget.cursorOpacityAnimates) {
-      // If we want to show the cursor, we will animate the opacity to the value
-      // of 1.0, and likewise if we want to make it disappear, to 0.0. An easing
-      // curve is used for the animation to mimic the aesthetics of the native
-      // iOS cursor.
-      //
-      // These values and curves have been obtained through eyeballing, so are
-      // likely not exactly the same as the values for native iOS.
-      _cursorBlinkOpacityController!.animateTo(targetOpacity, curve: Curves.easeOut);
-    } else {
-      _cursorBlinkOpacityController!.value = targetOpacity;
-    }
-
-    if (_obscureShowCharTicksPending > 0) {
-      setState(() {
-        _obscureShowCharTicksPending = WidgetsBinding.instance.platformDispatcher.brieflyShowPassword
-          ? _obscureShowCharTicksPending - 1
-          : 0;
-      });
-    }
-  }
-
-  void _cursorWaitForStart(Timer timer) {
-    assert(_kCursorBlinkHalfPeriod > _fadeDuration);
-    assert(!EditableText.debugDeterministicCursor);
-    _cursorTimer?.cancel();
-    _cursorTimer = Timer.periodic(_kCursorBlinkHalfPeriod, _cursorTick);
-  }
-
   // Indicates whether the cursor should be blinking right now (but it may
   // actually not blink because it's disabled via TickerMode.of(context)).
   bool _cursorActive = false;
 
-  void _startCursorTimer() {
-    assert(_cursorTimer == null);
+  void _startCursorBlink() {
+    assert(!(_cursorTimer?.isActive ?? false) || !(_backingCursorBlinkOpacityController?.isAnimating ?? false));
     _cursorActive = true;
     if (!_tickersEnabled) {
       return;
     }
-    _targetCursorVisibility = true;
-    _cursorBlinkOpacityController!.value = 1.0;
+    _cursorTimer?.cancel();
+    _cursorBlinkOpacityController.value = 1.0;
     if (EditableText.debugDeterministicCursor) {
       return;
     }
     if (widget.cursorOpacityAnimates) {
-      _cursorTimer = Timer.periodic(_kCursorBlinkWaitForStart, _cursorWaitForStart);
+      _cursorBlinkOpacityController.animateWith(_iosBlinkCursorSimulation).whenComplete(_onCursorTick);
     } else {
-      _cursorTimer = Timer.periodic(_kCursorBlinkHalfPeriod, _cursorTick);
+      _cursorTimer = Timer.periodic(_kCursorBlinkHalfPeriod, (Timer timer) { _onCursorTick(); });
     }
   }
 
-  void _stopCursorTimer({ bool resetCharTicks = true }) {
+  void _onCursorTick() {
+    if (_obscureShowCharTicksPending > 0) {
+      _obscureShowCharTicksPending = WidgetsBinding.instance.platformDispatcher.brieflyShowPassword
+        ? _obscureShowCharTicksPending - 1
+        : 0;
+      if (_obscureShowCharTicksPending == 0) {
+        setState(() { });
+      }
+    }
+
+    if (widget.cursorOpacityAnimates) {
+      _cursorTimer?.cancel();
+      // Schedule this as an async task to avoid blocking tester.pumpAndSettle
+      // indefinitely.
+      _cursorTimer = Timer(Duration.zero, () => _cursorBlinkOpacityController.animateWith(_iosBlinkCursorSimulation).whenComplete(_onCursorTick));
+    } else {
+      if (!(_cursorTimer?.isActive ?? false) && _tickersEnabled) {
+        _cursorTimer = Timer.periodic(_kCursorBlinkHalfPeriod, (Timer timer) { _onCursorTick(); });
+      }
+      _cursorBlinkOpacityController.value = _cursorBlinkOpacityController.value == 0 ? 1 : 0;
+    }
+  }
+
+  void _stopCursorBlink({ bool resetCharTicks = true }) {
     _cursorActive = false;
-    _cursorTimer?.cancel();
-    _cursorTimer = null;
-    _targetCursorVisibility = false;
-    _cursorBlinkOpacityController!.value = 0.0;
+    _cursorBlinkOpacityController.value = 0.0;
     if (EditableText.debugDeterministicCursor) {
       return;
     }
+    _cursorBlinkOpacityController.value = 0.0;
     if (resetCharTicks) {
       _obscureShowCharTicksPending = 0;
     }
-    if (widget.cursorOpacityAnimates) {
-      _cursorBlinkOpacityController!.stop();
-      _cursorBlinkOpacityController!.value = 0.0;
-    }
   }
 
   void _startOrStopCursorTimerIfNeeded() {
     if (_cursorTimer == null && _hasFocus && _value.selection.isCollapsed) {
-      _startCursorTimer();
-    } else if (_cursorActive && (!_hasFocus || !_value.selection.isCollapsed)) {
-      _stopCursorTimer();
+      _startCursorBlink();
+    }
+    else if (_cursorActive && (!_hasFocus || !_value.selection.isCollapsed)) {
+      _stopCursorBlink();
     }
   }
 
@@ -3488,8 +3552,10 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
       String text = _value.text;
       text = widget.obscuringCharacter * text.length;
       // Reveal the latest character in an obscured field only on mobile.
+      // Newer verions of iOS (iOS 15+) no longer reveal the most recently
+      // entered character.
       const Set<TargetPlatform> mobilePlatforms = <TargetPlatform> {
-        TargetPlatform.android, TargetPlatform.iOS, TargetPlatform.fuchsia,
+        TargetPlatform.android, TargetPlatform.fuchsia,
       };
       final bool breiflyShowPassword = WidgetsBinding.instance.platformDispatcher.brieflyShowPassword
                                     && mobilePlatforms.contains(defaultTargetPlatform);