gtk: make sure that window-decoration is honored on all paths (#4130)

Fix a regression from #4110 .

src/apprt/gtk/Window.zig

@@ -156,6 +156,9 @@ pub fn init(self: *Window, app: *App) !void {
     if (app.config.@"gtk-titlebar") {
         const header = HeaderBar.init(self);
 
+        // If we are not decorated then we hide the titlebar.
+        header.setVisible(app.config.@"window-decoration");
+
         {
             const btn = c.gtk_menu_button_new();
             c.gtk_widget_set_tooltip_text(btn, "Main Menu");
@@ -298,11 +301,6 @@ pub fn init(self: *Window, app: *App) !void {
         if (self.header) |header| {
             const header_widget = header.asWidget();
             c.adw_toolbar_view_add_top_bar(toolbar_view, header_widget);
-
-            // If we are not decorated then we hide the titlebar.
-            if (!app.config.@"window-decoration") {
-                c.gtk_widget_set_visible(header_widget, 0);
-            }
         }
 
         if (self.app.config.@"gtk-tabs-location" != .hidden) {
@@ -516,13 +514,19 @@ pub fn toggleWindowDecorations(self: *Window) void {
     const new_decorated = !old_decorated;
     c.gtk_window_set_decorated(self.window, @intFromBool(new_decorated));
 
+    // Fix any artifacting that may occur in window corners.
+    if (new_decorated) {
+        c.gtk_widget_add_css_class(@ptrCast(self.window), "without-window-decoration-and-with-titlebar");
+    } else {
+        c.gtk_widget_remove_css_class(@ptrCast(self.window), "without-window-decoration-and-with-titlebar");
+    }
+
     // If we have a titlebar, then we also show/hide it depending on the
     // decorated state. GTK tends to consider the titlebar part of the frame
     // and hides it with decorations, but libadwaita doesn't. This makes it
     // explicit.
-    if (self.header) |v| {
-        const widget = v.asWidget();
-        c.gtk_widget_set_visible(widget, @intFromBool(new_decorated));
+    if (self.header) |headerbar| {
+        headerbar.setVisible(new_decorated);
     }
 }
 

src/apprt/gtk/headerbar.zig

@@ -30,6 +30,10 @@ pub const HeaderBar = union(enum) {
         return .{ .gtk = @ptrCast(headerbar) };
     }
 
+    pub fn setVisible(self: HeaderBar, visible: bool) void {
+        c.gtk_widget_set_visible(self.asWidget(), @intFromBool(visible));
+    }
+
     pub fn asWidget(self: HeaderBar) *c.GtkWidget {
         return switch (self) {
             .adw => |headerbar| @ptrCast(@alignCast(headerbar)),