On Wayland, fix hiding cursors on GNOME

`wl_pointer::set_cursor` expects a serial number of the last
`wl_pointer::enter` event. However other calls expect latest
observed pointer serial, so this commit tracks both and
use them as required by specification.

Fixes #2273.

CHANGELOG.md

@@ -8,6 +8,7 @@ And please only add new entries to the top of this list, right below the `# Unre
 
 # Unreleased
 
+- On Wayland, fix bug where the cursor wouldn't hide in GNOME.
 - On macOS, Windows, and Wayland, add `set_cursor_hittest` to let the window ignore mouse events.
 - On Windows, added `WindowExtWindows::set_skip_taskbar` and `WindowBuilderExtWindows::with_skip_taskbar`.
 - On Windows, added `EventLoopBuilderExtWindows::with_msg_hook`.

src/platform_impl/linux/wayland/seat/pointer/data.rs

@@ -26,9 +26,12 @@ pub(super) struct PointerData {
 
     pub confined_pointer: Rc<RefCell<Option<ZwpConfinedPointerV1>>>,
 
-    /// A latest event serial.
+    /// Latest observed serial in pointer events.
     pub latest_serial: Rc<Cell<u32>>,
 
+    /// Latest observed serial in pointer enter events.
+    pub latest_enter_serial: Rc<Cell<u32>>,
+
     /// The currently accumulated axis data on a pointer.
     pub axis_data: AxisData,
 }
@@ -42,6 +45,7 @@ impl PointerData {
         Self {
             surface: None,
             latest_serial: Rc::new(Cell::new(0)),
+            latest_enter_serial: Rc::new(Cell::new(0)),
             confined_pointer,
             modifiers_state,
             pointer_constraints,

src/platform_impl/linux/wayland/seat/pointer/handlers.rs

@@ -42,6 +42,7 @@ pub(super) fn handle_pointer(
             ..
         } => {
             pointer_data.latest_serial.replace(serial);
+            pointer_data.latest_enter_serial.replace(serial);
 
             let window_id = wayland::make_wid(&surface);
             if !winit_state.window_map.contains_key(&window_id) {
@@ -61,6 +62,7 @@ pub(super) fn handle_pointer(
                 confined_pointer: Rc::downgrade(&pointer_data.confined_pointer),
                 pointer_constraints: pointer_data.pointer_constraints.clone(),
                 latest_serial: pointer_data.latest_serial.clone(),
+                latest_enter_serial: pointer_data.latest_enter_serial.clone(),
                 seat,
             };
             window_handle.pointer_entered(winit_pointer);
@@ -104,6 +106,7 @@ pub(super) fn handle_pointer(
                 confined_pointer: Rc::downgrade(&pointer_data.confined_pointer),
                 pointer_constraints: pointer_data.pointer_constraints.clone(),
                 latest_serial: pointer_data.latest_serial.clone(),
+                latest_enter_serial: pointer_data.latest_enter_serial.clone(),
                 seat,
             };
             window_handle.pointer_left(winit_pointer);

src/platform_impl/linux/wayland/seat/pointer/mod.rs

@@ -35,7 +35,11 @@ pub struct WinitPointer {
     confined_pointer: Weak<RefCell<Option<ZwpConfinedPointerV1>>>,
 
     /// Latest observed serial in pointer events.
+    /// used by Window::start_interactive_move()
     latest_serial: Rc<Cell<u32>>,
+    /// Latest observed serial in pointer enter events.
+    /// used by Window::set_cursor()
+    latest_enter_serial: Rc<Cell<u32>>,
 
     /// Seat.
     seat: WlSeat,
@@ -58,7 +62,9 @@ impl WinitPointer {
             Some(cursor_icon) => cursor_icon,
             None => {
                 // Hide the cursor.
-                (*self.pointer).set_cursor(self.latest_serial.get(), None, 0, 0);
+                // WlPointer::set_cursor() expects the serial of the last *enter*
+                // event (compare to to start_interactive_move()).
+                (*self.pointer).set_cursor(self.latest_enter_serial.get(), None, 0, 0);
                 return;
             }
         };
@@ -106,7 +112,7 @@ impl WinitPointer {
             CursorIcon::ZoomOut => &["zoom-out"],
         };
 
-        let serial = Some(self.latest_serial.get());
+        let serial = Some(self.latest_enter_serial.get());
         for cursor in cursors {
             if self.pointer.set_cursor(cursor, serial).is_ok() {
                 return;
@@ -151,6 +157,8 @@ impl WinitPointer {
     }
 
     pub fn drag_window(&self, window: &Window<FallbackFrame>) {
+        // WlPointer::setart_interactive_move() expects the last serial of *any*
+        // pointer event (compare to set_cursor()).
         window.start_interactive_move(&self.seat, self.latest_serial.get());
     }
 }