fix: resolve Linux window close handler to prevent app hang (#1795)

- Add delete-event callback that properly quits the application when window is closed

linux/CMakeLists.txt

@@ -1,6 +1,6 @@
 # Project-level configuration.
 cmake_minimum_required(VERSION 3.13)
-project(runner LANGUAGES CXX)
+project(runner LANGUAGES C CXX)
 
 # The name of the executable created for the application. Change this to change
 # the on-disk name of your application.

linux/runner/my_application.cc

@@ -20,6 +20,18 @@ static void first_frame_cb(MyApplication* self, FlView *view)
   gtk_widget_show(gtk_widget_get_toplevel(GTK_WIDGET(view)));
 }
 
+// Called when window is requested to be closed.
+static gboolean window_delete_event_cb(GtkWidget *widget, GdkEvent *event,
+                                       gpointer data) {
+  // Get the application and quit it.
+  GtkApplication *app = gtk_window_get_application(GTK_WINDOW(widget));
+  if (app != nullptr) {
+    g_application_quit(G_APPLICATION(app));
+  }
+  // Return TRUE to prevent further processing of the delete event.
+  return TRUE;
+}
+
 // Implements GApplication::activate.
 static void my_application_activate(GApplication* application) {
   MyApplication* self = MY_APPLICATION(application);
@@ -71,6 +83,9 @@ static void my_application_activate(GApplication* application) {
   g_signal_connect_swapped(view, "first-frame", G_CALLBACK(first_frame_cb), self);
   gtk_widget_realize(GTK_WIDGET(view));
 
+  // Connect the delete-event signal to handle window close.
+  g_signal_connect(window, "delete-event", G_CALLBACK(window_delete_event_cb), NULL);
+
   fl_register_plugins(FL_PLUGIN_REGISTRY(view));
 
   gtk_widget_grab_focus(GTK_WIDGET(view));