GTK: Open the dialog window on the same GdkScreen as the parent (#145)

Setting the default GdkDisplay doesn't actually cause a newly opened dialog window to use it. The more correct way seems to be to make the dialog window use the same GdkScreen as the parent. Each GdkScreen maps to one GdkDisplay, so this guarantees that the dialog window uses the same GdkDisplay as the parent too.

src/nfd_gtk.cpp

@@ -384,9 +384,7 @@ gint RunDialogWithFocus(GtkDialog* dialog) {
 // Gets the GdkWindow from the given window handle.  This function might fail even if parentWindow
 // is set correctly, since it calls some failable GDK functions.  If it fails, it will return
 // nullptr.  The caller is responsible for freeing ths returned GdkWindow, if not nullptr.
-GdkWindow* GetAllocNativeWindowHandle(const nfdwindowhandle_t& parentWindow,
-                                      GdkDisplayManager*& outDisplayManager,
-                                      GdkDisplay*& outDisplay) {
+GdkWindow* GetAllocNativeWindowHandle(const nfdwindowhandle_t& parentWindow) {
     switch (parentWindow.type) {
 #if defined(GDK_WINDOWING_X11)
         case NFD_WINDOW_HANDLE_TYPE_X11: {
@@ -434,8 +432,6 @@ GdkWindow* GetAllocNativeWindowHandle(const nfdwindowhandle_t& parentWindow,
                 gdk_set_allowed_backends(NULL);
             }
             if (!x11_display) return nullptr;
-            outDisplayManager = display_manager;
-            outDisplay = x11_display;
             GdkWindow* gdk_window = gdk_x11_window_foreign_new_for_display(x11_display, x11_handle);
             return gdk_window;
         }
@@ -452,39 +448,29 @@ void RealizedSignalHandler(GtkWidget* window, void* userdata) {
 
 struct NativeWindowParenter {
     NativeWindowParenter(GtkWidget* widget, const nfdwindowhandle_t& parentWindow) noexcept
-        : widget(widget), displayManager(nullptr) {
-        GdkDisplay* new_display = nullptr;
-        parent = GetAllocNativeWindowHandle(parentWindow, displayManager, new_display);
+        : widget(widget) {
+        parent = GetAllocNativeWindowHandle(parentWindow);
 
         if (parent) {
-            /* set the handler to the realize signal to set the transient GDK parent */
+            // set the handler to the realize signal to set the transient GDK parent
             handlerID = g_signal_connect(G_OBJECT(widget),
                                          "realize",
                                          G_CALLBACK(RealizedSignalHandler),
                                          static_cast<void*>(parent));
 
-            /* Set the default display to a display that we know is X11 (so that realizing the file
-             * dialog will use it) */
-            /* Note: displayManager here must be non-null since parent is non-null */
-            originalDisplay = gdk_display_manager_get_default_display(displayManager);
-            gdk_display_manager_set_default_display(displayManager, new_display);
+            // make the dialog window use the same GtkScreen as the parent (so that parenting works)
+            gtk_window_set_screen(GTK_WINDOW(widget), gdk_window_get_screen(parent));
         }
     }
     ~NativeWindowParenter() {
         if (parent) {
-            /* Set the default display back to whatever it was, to be nice */
-            /* Note: displayManager here must be non-null since parent is non-null */
-            gdk_display_manager_set_default_display(displayManager, originalDisplay);
-
-            /* unset the handler and delete the parent GdkWindow */
+            // unset the handler and delete the parent GdkWindow
             g_signal_handler_disconnect(G_OBJECT(widget), handlerID);
             g_object_unref(parent);
         }
     }
     GtkWidget* const widget;
     GdkWindow* parent;
-    GdkDisplayManager* displayManager;
-    GdkDisplay* originalDisplay;
     gulong handlerID;
 };