Fix inertia cancel event on macOS Ventura (flutter#37067)

* Fix inertia cancel event on macOS Ventura

* Increase allowed time delay on event to 50 ms

* Address feedback

Author: moffatman

shell/platform/darwin/macos/framework/Source/FlutterViewController.mm

@@ -28,6 +28,11 @@
 static constexpr int32_t kMousePointerDeviceId = 0;
 static constexpr int32_t kPointerPanZoomDeviceId = 1;
 
+// A trackpad touch following inertial scrolling should cause an inertia cancel
+// event to be issued. Use a window of 50 milliseconds after the scroll to account
+// for delays in event propagation observed in macOS Ventura.
+static constexpr double kTrackpadTouchInertiaCancelWindowMs = 0.050;
+
 /**
  * State tracking for mouse events, to adapt between the events coming from the system and the
  * events that the embedding API expects.
@@ -91,9 +96,9 @@
   bool rotate_gesture_active = false;
 
   /**
-   * System scroll inertia is currently sending us events.
+   * Time of last scroll momentum event.
    */
-  bool system_scroll_inertia_active = false;
+  NSTimeInterval last_scroll_momentum_changed_time = 0;
 
   /**
    * Resets all gesture state to default values.
@@ -521,11 +526,11 @@ - (void)dispatchGestureEvent:(nonnull NSEvent*)event {
   } else if (event.phase == NSEventPhaseNone && event.momentumPhase == NSEventPhaseNone) {
     [self dispatchMouseEvent:event phase:kHover];
   } else {
-    if (event.momentumPhase == NSEventPhaseBegan) {
-      _mouseState.system_scroll_inertia_active = true;
-    } else if (event.momentumPhase == NSEventPhaseEnded ||
-               event.momentumPhase == NSEventPhaseCancelled) {
-      _mouseState.system_scroll_inertia_active = false;
+    // Waiting until the first momentum change event is a workaround for an issue where
+    // touchesBegan: is called unexpectedly while in low power mode within the interval between
+    // momentum start and the first momentum change.
+    if (event.momentumPhase == NSEventPhaseChanged) {
+      _mouseState.last_scroll_momentum_changed_time = event.timestamp;
     }
     // Skip momentum update events, the framework will generate scroll momentum.
     NSAssert(event.momentumPhase != NSEventPhaseNone,
@@ -549,6 +554,8 @@ - (void)dispatchMouseEvent:(NSEvent*)event phase:(FlutterPointerPhase)phase {
                               _mouseState.rotate_gesture_active;
     if (event.type == NSEventTypeScrollWheel) {
       _mouseState.pan_gesture_active = true;
+      // Ensure scroll inertia cancel event is not sent afterwards.
+      _mouseState.last_scroll_momentum_changed_time = 0;
     } else if (event.type == NSEventTypeMagnify) {
       _mouseState.scale_gesture_active = true;
     } else if (event.type == NSEventTypeRotate) {
@@ -841,8 +848,9 @@ - (void)swipeWithEvent:(NSEvent*)event {
 - (void)touchesBeganWithEvent:(NSEvent*)event {
   NSTouch* touch = event.allTouches.anyObject;
   if (touch != nil) {
-    if (_mouseState.system_scroll_inertia_active) {
-      // The trackpad has been touched and a scroll gesture is still sending inertia events.
+    if ((event.timestamp - _mouseState.last_scroll_momentum_changed_time) <
+        kTrackpadTouchInertiaCancelWindowMs) {
+      // The trackpad has been touched following a scroll momentum event.
       // A scroll inertia cancel message should be sent to the framework.
       NSPoint locationInView = [self.flutterView convertPoint:event.locationInWindow fromView:nil];
       NSPoint locationInBackingCoordinates =
@@ -858,6 +866,8 @@ - (void)touchesBeganWithEvent:(NSEvent*)event {
       };
 
       [_engine sendPointerEvent:flutterEvent];
+      // Ensure no further scroll inertia cancel event will be sent.
+      _mouseState.last_scroll_momentum_changed_time = 0;
     }
   }
 }

shell/platform/darwin/macos/framework/Source/FlutterViewControllerTest.mm

@@ -541,17 +541,39 @@ - (bool)testTrackpadGesturesAreSentToFramework {
   [viewController scrollWheel:[NSEvent eventWithCGEvent:cgEventMomentumStart]];
   EXPECT_FALSE(called);
 
+  // Advance system momentum.
+  CGEventRef cgEventMomentumUpdate = CGEventCreateCopy(cgEventStart);
+  CGEventSetIntegerValueField(cgEventMomentumUpdate, kCGScrollWheelEventScrollPhase, 0);
+  CGEventSetIntegerValueField(cgEventMomentumUpdate, kCGScrollWheelEventMomentumPhase,
+                              kCGMomentumScrollPhaseContinue);
+
+  called = false;
+  [viewController scrollWheel:[NSEvent eventWithCGEvent:cgEventMomentumUpdate]];
+  EXPECT_FALSE(called);
+
   // Mock a touch on the trackpad.
   id touchMock = OCMClassMock([NSTouch class]);
   NSSet* touchSet = [NSSet setWithObject:touchMock];
-  id touchEventMock = OCMClassMock([NSEvent class]);
-  OCMStub([touchEventMock allTouches]).andReturn(touchSet);
+  id touchEventMock1 = OCMClassMock([NSEvent class]);
+  OCMStub([touchEventMock1 allTouches]).andReturn(touchSet);
   CGPoint touchLocation = {0, 0};
-  OCMStub([touchEventMock locationInWindow]).andReturn(touchLocation);
+  OCMStub([touchEventMock1 locationInWindow]).andReturn(touchLocation);
+  OCMStub([(NSEvent*)touchEventMock1 timestamp]).andReturn(0.150);  // 150 milliseconds.
+
+  // Scroll inertia cancel event should not be issued (timestamp too far in the future).
+  called = false;
+  [viewController touchesBeganWithEvent:touchEventMock1];
+  EXPECT_FALSE(called);
+
+  // Mock another touch on the trackpad.
+  id touchEventMock2 = OCMClassMock([NSEvent class]);
+  OCMStub([touchEventMock2 allTouches]).andReturn(touchSet);
+  OCMStub([touchEventMock2 locationInWindow]).andReturn(touchLocation);
+  OCMStub([(NSEvent*)touchEventMock2 timestamp]).andReturn(0.005);  // 5 milliseconds.
 
   // Scroll inertia cancel event should be issued.
   called = false;
-  [viewController touchesBeganWithEvent:touchEventMock];
+  [viewController touchesBeganWithEvent:touchEventMock2];
   EXPECT_TRUE(called);
   EXPECT_EQ(last_event.signal_kind, kFlutterPointerSignalKindScrollInertiaCancel);
   EXPECT_EQ(last_event.device_kind, kFlutterPointerDeviceKindTrackpad);
@@ -566,11 +588,6 @@ - (bool)testTrackpadGesturesAreSentToFramework {
   [viewController scrollWheel:[NSEvent eventWithCGEvent:cgEventMomentumEnd]];
   EXPECT_FALSE(called);
 
-  // Scroll inertia cancel event should not be issued after momentum has ended.
-  called = false;
-  [viewController touchesBeganWithEvent:touchEventMock];
-  EXPECT_FALSE(called);
-
   // May-begin and cancel are used while macOS determines which type of gesture to choose.
   CGEventRef cgEventMayBegin = CGEventCreateCopy(cgEventStart);
   CGEventSetIntegerValueField(cgEventMayBegin, kCGScrollWheelEventScrollPhase,