Refactor macOS trackpad gesture tracking

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

@@ -80,20 +80,25 @@
    */
   bool has_pending_exit = false;
 
+  /*
+   * Whether or not a kPanZoomStart has been sent since the last kAdd/kPanZoomEnd.
+   */
+  bool flutter_state_is_pan_zoom_started = false;
+
   /**
-   * Pan gesture is currently sending us events.
+   * State of pan gesture.
    */
-  bool pan_gesture_active = false;
+  NSEventPhase pan_gesture_phase = NSEventPhaseNone;
 
   /**
-   * Scale gesture is currently sending us events.
+   * State of scale gesture.
    */
-  bool scale_gesture_active = false;
+  NSEventPhase scale_gesture_phase = NSEventPhaseNone;
 
   /**
-   * Rotate gesture is currently sending use events.
+   * State of rotate gesture.
    */
-  bool rotate_gesture_active = false;
+  NSEventPhase rotate_gesture_phase = NSEventPhaseNone;
 
   /**
    * Time of last scroll momentum event.
@@ -108,6 +113,10 @@ void GestureReset() {
     delta_y = 0;
     scale = 0;
     rotation = 0;
+    flutter_state_is_pan_zoom_started = false;
+    pan_gesture_phase = NSEventPhaseNone;
+    scale_gesture_phase = NSEventPhaseNone;
+    rotate_gesture_phase = NSEventPhaseNone;
   }
 
   /**
@@ -679,32 +688,42 @@ - (void)dispatchMouseEvent:(NSEvent*)event phase:(FlutterPointerPhase)phase {
 
   // Multiple gesture recognizers could be active at once, we can't send multiple kPanZoomStart.
   // For example: rotation and magnification.
+  if (phase == kPanZoomStart || phase == kPanZoomEnd) {
+    if (event.type == NSEventTypeScrollWheel) {
+      _mouseState.pan_gesture_phase = event.phase;
+    } else if (event.type == NSEventTypeMagnify) {
+      _mouseState.scale_gesture_phase = event.phase;
+    } else if (event.type == NSEventTypeRotate) {
+      _mouseState.rotate_gesture_phase = event.phase;
+    }
+  }
   if (phase == kPanZoomStart) {
-    bool gestureAlreadyDown = _mouseState.pan_gesture_active || _mouseState.scale_gesture_active ||
-                              _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) {
-      _mouseState.rotate_gesture_active = true;
     }
-    if (gestureAlreadyDown) {
+    if (_mouseState.flutter_state_is_pan_zoom_started) {
+      // Already started on a previous gesture type
       return;
     }
+    _mouseState.flutter_state_is_pan_zoom_started = true;
   }
   if (phase == kPanZoomEnd) {
-    if (event.type == NSEventTypeScrollWheel) {
-      _mouseState.pan_gesture_active = false;
-    } else if (event.type == NSEventTypeMagnify) {
-      _mouseState.scale_gesture_active = false;
-    } else if (event.type == NSEventTypeRotate) {
-      _mouseState.rotate_gesture_active = false;
+    if (!_mouseState.flutter_state_is_pan_zoom_started) {
+      // NSEventPhaseCancelled is sometimes received at incorrect times in the state
+      // machine, just ignore it here if it doesn't make sense
+      // (we have no active gesture to cancel).
+      NSAssert(event.phase == NSEventPhaseCancelled,
+               @"Received gesture event with unexpected phase");
+      return;
     }
-    if (_mouseState.pan_gesture_active || _mouseState.scale_gesture_active ||
-        _mouseState.rotate_gesture_active) {
+    // NSEventPhase values are powers of two, we can use this to inspect merged phases.
+    NSEventPhase all_gestures_fields = _mouseState.pan_gesture_phase |
+                                       _mouseState.scale_gesture_phase |
+                                       _mouseState.rotate_gesture_phase;
+    NSEventPhase active_mask = NSEventPhaseBegan | NSEventPhaseChanged;
+    if ((all_gestures_fields & active_mask) != 0) {
+      // Even though this gesture type ended, a different type is still active.
       return;
     }
   }

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

@@ -995,6 +995,12 @@ - (bool)testTrackpadGesturesAreSentToFramework:(id)engineMock {
   EXPECT_EQ(last_event.device_kind, kFlutterPointerDeviceKindTrackpad);
   EXPECT_EQ(last_event.signal_kind, kFlutterPointerSignalKindNone);
 
+  // Test that stray NSEventPhaseCancelled event does not crash
+  called = false;
+  [viewController rotateWithEvent:flutter::testing::MockGestureEvent(NSEventTypeRotate,
+                                                                     NSEventPhaseCancelled, 0, 0)];
+  EXPECT_FALSE(called);
+
   return true;
 }