Fix menu positioning to use pointer window coordinates

Menu positioning now uses the window under the pointer to avoid coordinate space mismatches. This ensures the menu appears at the correct location relative to the user's cursor, improving reliability across different GTK versions.

Author: lijy91

src/platform/linux/menu_linux.cpp

@@ -682,18 +682,31 @@ bool Menu::Open(const PositioningStrategy& strategy, Placement placement) {
 
   // Calculate position based on strategy type
   if (strategy.GetType() == PositioningStrategy::Type::CursorPosition) {
-    // Use mouse position
-    GdkDevice* mouse_device;
+    // Position relative to the window under the pointer to avoid coord space mismatches
+    int x = 0, y = 0;
+    GdkWindow* pointer_window = nullptr;
 #if GTK_CHECK_VERSION(3, 20, 0)
-    GdkSeat* seat = gdk_display_get_default_seat(gdk_display_get_default());
-    mouse_device = gdk_seat_get_pointer(seat);
+    GdkDisplay* display = gdk_display_get_default();
+    GdkSeat* seat = display ? gdk_display_get_default_seat(display) : nullptr;
+    GdkDevice* pointer = seat ? gdk_seat_get_pointer(seat) : nullptr;
+    if (pointer) {
+      pointer_window = gdk_device_get_window_at_position(pointer, &x, &y);
+    }
 #else
-    GdkDeviceManager* devman =
-        gdk_display_get_device_manager(gdk_display_get_default());
-    mouse_device = gdk_device_manager_get_client_pointer(devman);
+    GdkDeviceManager* devman = gdk_display_get_device_manager(gdk_display_get_default());
+    GdkDevice* pointer = gdk_device_manager_get_client_pointer(devman);
+    if (pointer) {
+      GdkScreen* screen = nullptr;
+      gdk_device_get_position(pointer, &screen, &x, &y);  // screen coords
+      pointer_window = gdk_get_default_root_window();
+    }
 #endif
-    int x, y;
-    gdk_window_get_device_position(gdk_window, mouse_device, &x, &y, nullptr);
+    if (pointer_window) {
+      gdk_window = pointer_window;  // ensure rect coords match this window
+    } else if (!gdk_window) {
+      gdk_window = gdk_get_default_root_window();
+    }
+
     rectangle.x = x;
     rectangle.y = y;
     rectangle.width = 1;