gtkwindow: Use window-manager-side window menus

This avoids a bunch of policy problems with deciding how to lay
out the window menu under different WMs.

For now, we use the special event _GTK_SHOW_WINDOW_MENU, but we
hope to have this standardized in wm-spec quite soon, as KDE wants
it as well.

gdk/gdkwindow.c

@@ -10921,3 +10921,36 @@ gdk_window_set_shadow_width (GdkWindow *window,
   if (impl_class->set_shadow_width)
     impl_class->set_shadow_width (window, left, right, top, bottom);
 }
+
+/**
+ * gdk_window_show_window_menu:
+ * @window: a #GdkWindow
+ * @event: a #GdkEvent to show the menu for
+ *
+ * Asks the window menu to show the window menu. The window menu is
+ * the menu shown when right-clicking the titlebar on traditional
+ * windows managed by the window manager. This is useful for windows
+ * using client-side decorations, activating it with a right-click
+ * on the window decorations.
+ *
+ * Returns: %TRUE if the window menu was shown by the window
+ * manager and %FALSE otherwise.
+ *
+ * Since: 3.14
+ */
+gboolean
+gdk_window_show_window_menu (GdkWindow *window,
+                             GdkEvent  *event)
+{
+  GdkWindowImplClass *impl_class;
+
+  g_return_val_if_fail (GDK_IS_WINDOW (window), FALSE);
+  g_return_val_if_fail (!GDK_WINDOW_DESTROYED (window), FALSE);
+
+  impl_class = GDK_WINDOW_IMPL_GET_CLASS (window->impl);
+
+  if (impl_class->show_window_menu)
+    return impl_class->show_window_menu (window, event);
+  else
+    return FALSE;
+}

gdk/gdkwindow.h

@@ -1100,6 +1100,9 @@ void       gdk_window_set_shadow_width         (GdkWindow      *window,
                                                 gint            right,
                                                 gint            top,
                                                 gint            bottom);
+GDK_AVAILABLE_IN_3_14
+gboolean  gdk_window_show_window_menu          (GdkWindow      *window,
+                                                GdkEvent       *event);
 
 G_END_DECLS
 

gdk/gdkwindowimpl.h

@@ -301,6 +301,8 @@ struct _GdkWindowImplClass
                                            gint            right,
                                            gint            top,
                                            gint            bottom);
+  gboolean     (* show_window_menu)       (GdkWindow      *window,
+                                           GdkEvent       *event);
 };
 
 /* Interface Functions */

gdk/x11/gdkwindow-x11.c

@@ -5702,6 +5702,47 @@ gdk_x11_window_set_opaque_region (GdkWindow      *window,
     g_free (data);
 }
 
+static gboolean
+gdk_x11_window_show_window_menu (GdkWindow *window,
+                                 GdkEvent  *event)
+{
+  GdkDisplay *display = GDK_WINDOW_DISPLAY (window);
+  GdkDevice *device;
+  int device_id;
+  XClientMessageEvent xclient = { 0 };
+
+  switch (event->type)
+    {
+    case GDK_BUTTON_PRESS:
+    case GDK_BUTTON_RELEASE:
+      break;
+    default:
+      return FALSE;
+    }
+
+  if (!gdk_x11_screen_supports_net_wm_hint (GDK_WINDOW_SCREEN (window),
+                                            gdk_atom_intern_static_string ("_GTK_SHOW_WINDOW_MENU")))
+    return FALSE;
+
+  device = gdk_event_get_device (event);
+
+  g_object_get (G_OBJECT (device),
+                "device-id", &device_id,
+                NULL);
+
+  xclient.type = ClientMessage;
+  xclient.window = GDK_WINDOW_XID (window);
+  xclient.message_type = gdk_x11_get_xatom_by_name_for_display (display, "_GTK_SHOW_WINDOW_MENU");
+  xclient.data.l[0] = device_id;
+  xclient.format = 32;
+
+  XSendEvent (GDK_DISPLAY_XDISPLAY (display), GDK_WINDOW_XROOTWIN (window), False,
+              SubstructureRedirectMask | SubstructureNotifyMask,
+              (XEvent *)&xclient);
+
+  return TRUE;
+}
+
 static void
 gdk_window_impl_x11_class_init (GdkWindowImplX11Class *klass)
 {
@@ -5791,4 +5832,5 @@ gdk_window_impl_x11_class_init (GdkWindowImplX11Class *klass)
   impl_class->get_scale_factor = gdk_x11_window_get_scale_factor;
   impl_class->set_opaque_region = gdk_x11_window_set_opaque_region;
   impl_class->set_shadow_width = gdk_x11_window_set_shadow_width;
+  impl_class->show_window_menu = gdk_x11_window_show_window_menu;
 }