Add mouse button support to the macOS shell (#9054)

Uses the new embedding API support for device type and buttons to pass
appropriate mouse button events, allowing for right click, middle click,
etc.

Also fixes some edge cases where macOS event delivery violated Flutter
requirements by tracking more data about the mouse event stream and
adjusting the sent events as necessary.

Author: stuartmorgan-g

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

@@ -16,6 +16,52 @@
 
 static const int kDefaultWindowFramebuffer = 0;
 
+namespace {
+
+/**
+ * State tracking for mouse events, to adapt between the events coming from the system and the
+ * events that the embedding API expects.
+ */
+struct MouseState {
+  /**
+   * Whether or not a kAdd event has been sent (or sent again since the last kRemove if tracking is
+   * enabled). Used to determine whether to send a kAdd event before sending an incoming mouse
+   * event, since Flutter expects pointers to be added before events are sent for them.
+   */
+  bool flutter_state_is_added = false;
+
+  /**
+   * Whether or not a kDown has been sent since the last kAdd/kUp.
+   */
+  bool flutter_state_is_down = false;
+
+  /**
+   * Whether or not mouseExited: was received while a button was down. Cocoa's behavior when
+   * dragging out of a tracked area is to send an exit, then keep sending drag events until the last
+   * button is released. If it was released inside the view, mouseEntered: is sent the next time the
+   * mouse moves. Flutter doesn't expect to receive events after a kRemove, so the kRemove for the
+   * exit needs to be delayed until after the last mouse button is released.
+   */
+  bool has_pending_exit = false;
+
+  /**
+   * The currently pressed buttons, as represented in FlutterPointerEvent.
+   */
+  int64_t buttons = 0;
+
+  /**
+   * Resets all state to default values.
+   */
+  void Reset() {
+    flutter_state_is_added = false;
+    flutter_state_is_down = false;
+    has_pending_exit = false;
+    buttons = 0;
+  }
+};
+
+}  // namespace
+
 #pragma mark - Private interface declaration.
 
 /**
@@ -34,12 +80,9 @@ @interface FLEViewController ()
 @property(nonatomic) NSTrackingArea* trackingArea;
 
 /**
- * Whether or not a kAdd event has been sent for the mouse (or sent again since
- * the last kRemove was sent if tracking is enabled). Used to determine whether
- * to send an Add event before sending an incoming mouse event, since Flutter
- * expects a pointers to be added before events are sent for them.
+ * The current state of the mouse and the sent mouse events.
  */
-@property(nonatomic) BOOL mouseCurrentlyAdded;
+@property(nonatomic) MouseState mouseState;
 
 /**
  * Updates |trackingArea| for the current tracking settings, creating it with
@@ -81,6 +124,13 @@ - (void)makeResourceContextCurrent;
  */
 - (void)handlePlatformMessage:(const FlutterPlatformMessage*)message;
 
+/**
+ * Calls dispatchMouseEvent:phase: with a phase determined by self.mouseState.
+ *
+ * mouseState.buttons should be updated before calling this method.
+ */
+- (void)dispatchMouseEvent:(nonnull NSEvent*)event;
+
 /**
  * Converts |event| to a FlutterPointerEvent with the given phase, and sends it to the engine.
  */
@@ -447,10 +497,24 @@ - (void)handlePlatformMessage:(const FlutterPlatformMessage*)message {
   }
 }
 
+- (void)dispatchMouseEvent:(nonnull NSEvent*)event {
+  FlutterPointerPhase phase = _mouseState.buttons == 0
+                                  ? (_mouseState.flutter_state_is_down ? kUp : kHover)
+                                  : (_mouseState.flutter_state_is_down ? kMove : kDown);
+  [self dispatchMouseEvent:event phase:phase];
+}
+
 - (void)dispatchMouseEvent:(NSEvent*)event phase:(FlutterPointerPhase)phase {
+  // There are edge cases where the system will deliver enter out of order relative to other
+  // events (e.g., drag out and back in, release, then click; mouseDown: will be called before
+  // mouseEntered:). Discard those events, since the add will already have been synthesized.
+  if (_mouseState.flutter_state_is_added && phase == kAdd) {
+    return;
+  }
+
   // If a pointer added event hasn't been sent, synthesize one using this event for the basic
   // information.
-  if (!_mouseCurrentlyAdded && phase != kAdd) {
+  if (!_mouseState.flutter_state_is_added && phase != kAdd) {
     // Only the values extracted for use in flutterEvent below matter, the rest are dummy values.
     NSEvent* addEvent = [NSEvent enterExitEventWithType:NSEventTypeMouseEntered
                                                location:event.locationInWindow
@@ -468,10 +532,13 @@ - (void)dispatchMouseEvent:(NSEvent*)event phase:(FlutterPointerPhase)phase {
   NSPoint locationInBackingCoordinates = [self.view convertPointToBacking:locationInView];
   FlutterPointerEvent flutterEvent = {
       .struct_size = sizeof(flutterEvent),
+      .device_kind = kFlutterPointerDeviceKindMouse,
       .phase = phase,
       .x = locationInBackingCoordinates.x,
       .y = -locationInBackingCoordinates.y,  // convertPointToBacking makes this negative.
       .timestamp = static_cast<size_t>(event.timestamp * NSEC_PER_MSEC),
+      // If a click triggered a synthesized kAdd, don't pass the buttons in that event.
+      .buttons = phase == kAdd ? 0 : _mouseState.buttons,
   };
 
   if (event.type == NSEventTypeScrollWheel) {
@@ -491,10 +558,19 @@ - (void)dispatchMouseEvent:(NSEvent*)event phase:(FlutterPointerPhase)phase {
   }
   FlutterEngineSendPointerEvent(_engine, &flutterEvent, 1);
 
-  if (phase == kAdd) {
-    _mouseCurrentlyAdded = YES;
+  // Update tracking of state as reported to Flutter.
+  if (phase == kDown) {
+    _mouseState.flutter_state_is_down = true;
+  } else if (phase == kUp) {
+    _mouseState.flutter_state_is_down = false;
+    if (_mouseState.has_pending_exit) {
+      [self dispatchMouseEvent:event phase:kRemove];
+      _mouseState.has_pending_exit = false;
+    }
+  } else if (phase == kAdd) {
+    _mouseState.flutter_state_is_added = true;
   } else if (phase == kRemove) {
-    _mouseCurrentlyAdded = NO;
+    _mouseState.Reset();
   }
 }
 
@@ -622,28 +698,62 @@ - (void)keyUp:(NSEvent*)event {
   }
 }
 
+- (void)mouseEntered:(NSEvent*)event {
+  [self dispatchMouseEvent:event phase:kAdd];
+}
+
+- (void)mouseExited:(NSEvent*)event {
+  if (_mouseState.buttons != 0) {
+    _mouseState.has_pending_exit = true;
+    return;
+  }
+  [self dispatchMouseEvent:event phase:kRemove];
+}
+
 - (void)mouseDown:(NSEvent*)event {
-  [self dispatchMouseEvent:event phase:kDown];
+  _mouseState.buttons |= kFlutterPointerButtonMousePrimary;
+  [self dispatchMouseEvent:event];
 }
 
 - (void)mouseUp:(NSEvent*)event {
-  [self dispatchMouseEvent:event phase:kUp];
+  _mouseState.buttons &= ~static_cast<uint64_t>(kFlutterPointerButtonMousePrimary);
+  [self dispatchMouseEvent:event];
 }
 
 - (void)mouseDragged:(NSEvent*)event {
-  [self dispatchMouseEvent:event phase:kMove];
+  [self dispatchMouseEvent:event];
 }
 
-- (void)mouseEntered:(NSEvent*)event {
-  [self dispatchMouseEvent:event phase:kAdd];
+- (void)rightMouseDown:(NSEvent*)event {
+  _mouseState.buttons |= kFlutterPointerButtonMouseSecondary;
+  [self dispatchMouseEvent:event];
 }
 
-- (void)mouseExited:(NSEvent*)event {
-  [self dispatchMouseEvent:event phase:kRemove];
+- (void)rightMouseUp:(NSEvent*)event {
+  _mouseState.buttons &= ~static_cast<uint64_t>(kFlutterPointerButtonMouseSecondary);
+  [self dispatchMouseEvent:event];
+}
+
+- (void)rightMouseDragged:(NSEvent*)event {
+  [self dispatchMouseEvent:event];
+}
+
+- (void)otherMouseDown:(NSEvent*)event {
+  _mouseState.buttons |= (1 << event.buttonNumber);
+  [self dispatchMouseEvent:event];
+}
+
+- (void)otherMouseUp:(NSEvent*)event {
+  _mouseState.buttons &= ~static_cast<uint64_t>(1 << event.buttonNumber);
+  [self dispatchMouseEvent:event];
+}
+
+- (void)otherMouseDragged:(NSEvent*)event {
+  [self dispatchMouseEvent:event];
 }
 
 - (void)mouseMoved:(NSEvent*)event {
-  [self dispatchMouseEvent:event phase:kHover];
+  [self dispatchMouseEvent:event];
 }
 
 - (void)scrollWheel:(NSEvent*)event {