macos: Add a hook to update stale modifiers

Sometimes, `ViewState` and `event` might have different values for their
stored `modifiers` flags.  These are internally stored as a bitmask in
the latter and an enum in the former.

We can check to see if they differ, and if they do, automatically
dispatch an event to update consumers of modifier state as well as the
stored `state.modifiers`.  That's what the hook does.

This hook is then called in the key_down, mouse_entered, mouse_exited,
mouse_click, scroll_wheel, and pressure_change_with_event callbacks,
which each will contain updated modifiers.

Signed-off-by: Kristofer Rye <[email protected]>

src/platform_impl/macos/view.rs

@@ -623,6 +623,18 @@ fn retrieve_keycode(event: id) -> Option<VirtualKeyCode> {
     })
 }
 
+// Update `state.modifiers` if `event` has something different
+fn update_potentially_stale_modifiers(state: &mut ViewState, event: id) {
+    if state.modifiers != event_mods(event) {
+        state.modifiers = event_mods(event);
+        trace!("Modifiers are stale; updating modifiers");
+        AppState::queue_event(EventWrapper::StaticEvent(Event::WindowEvent {
+            window_id: WindowId(get_window_id(state.ns_window)),
+            event: WindowEvent::ModifiersChanged(state.modifiers),
+        }));
+    }
+}
+
 extern "C" fn key_down(this: &Object, _sel: Sel, event: id) {
     trace!("Triggered `keyDown`");
     unsafe {
@@ -638,6 +650,8 @@ extern "C" fn key_down(this: &Object, _sel: Sel, event: id) {
 
         let is_repeat = msg_send![event, isARepeat];
 
+        update_potentially_stale_modifiers(state, event);
+
         #[allow(deprecated)]
         let window_event = Event::WindowEvent {
             window_id,
@@ -762,8 +776,6 @@ extern "C" fn flags_changed(this: &Object, _sel: Sel, event: id) {
             }));
         }
 
-        trace!("Queueing event with modifiers {:?}", state.modifiers);
-
         AppState::queue_event(EventWrapper::StaticEvent(Event::WindowEvent {
             // TODO Maybe memoize get_window_id if it's safe to reuse?
             window_id: WindowId(get_window_id(state.ns_window)),
@@ -834,6 +846,8 @@ fn mouse_click(this: &Object, event: id, button: MouseButton, button_state: Elem
         let state_ptr: *mut c_void = *this.get_ivar("winitState");
         let state = &mut *(state_ptr as *mut ViewState);
 
+        update_potentially_stale_modifiers(state, event);
+
         let window_event = Event::WindowEvent {
             window_id: WindowId(get_window_id(state.ns_window)),
             event: WindowEvent::MouseInput {
@@ -932,6 +946,8 @@ extern "C" fn mouse_entered(this: &Object, _sel: Sel, event: id) {
         let state_ptr: *mut c_void = *this.get_ivar("winitState");
         let state = &mut *(state_ptr as *mut ViewState);
 
+        update_potentially_stale_modifiers(state, event);
+
         let enter_event = Event::WindowEvent {
             window_id: WindowId(get_window_id(state.ns_window)),
             event: WindowEvent::CursorEntered {
@@ -945,12 +961,14 @@ extern "C" fn mouse_entered(this: &Object, _sel: Sel, event: id) {
     trace!("Completed `mouseEntered`");
 }
 
-extern "C" fn mouse_exited(this: &Object, _sel: Sel, _event: id) {
+extern "C" fn mouse_exited(this: &Object, _sel: Sel, event: id) {
     trace!("Triggered `mouseExited`");
     unsafe {
         let state_ptr: *mut c_void = *this.get_ivar("winitState");
         let state = &mut *(state_ptr as *mut ViewState);
 
+        update_potentially_stale_modifiers(state, event);
+
         let window_event = Event::WindowEvent {
             window_id: WindowId(get_window_id(state.ns_window)),
             event: WindowEvent::CursorLeft {
@@ -990,6 +1008,8 @@ extern "C" fn scroll_wheel(this: &Object, _sel: Sel, event: id) {
         let state_ptr: *mut c_void = *this.get_ivar("winitState");
         let state = &mut *(state_ptr as *mut ViewState);
 
+        update_potentially_stale_modifiers(state, event);
+
         let window_event = Event::WindowEvent {
             window_id: WindowId(get_window_id(state.ns_window)),
             event: WindowEvent::MouseWheel {
@@ -1012,6 +1032,8 @@ extern "C" fn pressure_change_with_event(this: &Object, _sel: Sel, event: id) {
         let state_ptr: *mut c_void = *this.get_ivar("winitState");
         let state = &mut *(state_ptr as *mut ViewState);
 
+        update_potentially_stale_modifiers(state, event);
+
         let pressure = event.pressure();
         let stage = event.stage();