Bug 1652220 [Linux] Create titlebar style from actual widget, r=jhorak

Differential Revision: https://phabricator.services.mozilla.com/D98597

widget/gtk/WidgetStyleCache.cpp

@@ -437,25 +437,37 @@ static GtkWidget* CreateNotebookWidget() {
   return widget;
 }
 
-static void CreateHeaderBarWidget(WidgetNodeType aAppearance) {
-  MOZ_ASSERT(sWidgetStorage[aAppearance] == nullptr,
-             "Header bar widget is already created!");
-
-  static auto sGtkHeaderBarNewPtr =
-      (GtkWidget * (*)()) dlsym(RTLD_DEFAULT, "gtk_header_bar_new");
-
-  GtkWidget* headerbar = sGtkHeaderBarNewPtr();
-  sWidgetStorage[aAppearance] = headerbar;
-
-  GtkWidget* window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
+void GtkWindowSetTitlebar(GtkWindow* aWindow, GtkWidget* aWidget) {
   static auto sGtkWindowSetTitlebar = (void (*)(GtkWindow*, GtkWidget*))dlsym(
       RTLD_DEFAULT, "gtk_window_set_titlebar");
-  MOZ_ASSERT(sGtkWindowSetTitlebar,
-             "Missing gtk_window_set_titlebar(), old Gtk+ library?");
-  sGtkWindowSetTitlebar(GTK_WINDOW(window), headerbar);
-  gtk_widget_realize(window);
+  sGtkWindowSetTitlebar(aWindow, aWidget);
+}
 
+GtkWidget* GtkHeaderBarNew() {
+  static auto sGtkHeaderBarNewPtr =
+      (GtkWidget * (*)()) dlsym(RTLD_DEFAULT, "gtk_header_bar_new");
+  return sGtkHeaderBarNewPtr();
+}
+
+bool IsSolidCSDStyleUsed() {
+  static bool isSolidCSDStyleUsed = []() {
+    GtkWidget* window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
+    GtkWindowSetTitlebar(GTK_WINDOW(window), GtkHeaderBarNew());
+    gtk_widget_realize(window);
+    GtkStyleContext* windowStyle = gtk_widget_get_style_context(window);
+    bool ret = gtk_style_context_has_class(windowStyle, "solid-csd");
+    gtk_widget_destroy(window);
+    return ret;
+  }();
+  return isSolidCSDStyleUsed;
+}
+
+static void CreateHeaderBarWidget(WidgetNodeType aAppearance) {
+  sWidgetStorage[aAppearance] = GtkHeaderBarNew();
+
+  GtkWidget* window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
   GtkStyleContext* style = gtk_widget_get_style_context(window);
+
   if (aAppearance == MOZ_GTK_HEADER_BAR_MAXIMIZED) {
     gtk_style_context_add_class(style, "maximized");
     MOZ_ASSERT(sWidgetStorage[MOZ_GTK_HEADERBAR_WINDOW_MAXIMIZED] == nullptr,
@@ -467,8 +479,17 @@ static void CreateHeaderBarWidget(WidgetNodeType aAppearance) {
     sWidgetStorage[MOZ_GTK_HEADERBAR_WINDOW] = window;
   }
 
+  // Headerbar has to be placed to window with csd or solid-csd style
+  // to properly draw the decorated.
+  gtk_style_context_add_class(style,
+                              IsSolidCSDStyleUsed() ? "solid-csd" : "csd");
+
+  GtkWidget* fixed = gtk_fixed_new();
+  gtk_container_add(GTK_CONTAINER(window), fixed);
+  gtk_container_add(GTK_CONTAINER(fixed), sWidgetStorage[aAppearance]);
+
   // Emulate what create_titlebar() at gtkwindow.c does.
-  style = gtk_widget_get_style_context(headerbar);
+  style = gtk_widget_get_style_context(sWidgetStorage[aAppearance]);
   gtk_style_context_add_class(style, "titlebar");
 
   // TODO: Define default-decoration titlebar style as workaround

widget/gtk/WidgetStyleCache.h

@@ -52,6 +52,8 @@ GtkStyleContext* CreateStyleContextWithStates(
 
 void ResetWidgetCache(void);
 
+bool IsSolidCSDStyleUsed();
+
 void StyleContextSetScale(GtkStyleContext* style, gint aScaleFactor);
 
 #endif  // WidgetStyleCache_h