fix: linux titlebar height on non-GNOME DEs

linux/runner/my_application.cc

@@ -1,10 +1,6 @@
 #include "my_application.h"
 
 #include <flutter_linux/flutter_linux.h>
-#ifdef GDK_WINDOWING_X11
-#include <gdk/gdkx.h>
-#endif
-
 #include "flutter/generated_plugin_registrant.h"
 #include "mpv/mpv_plugin.h"
 
@@ -22,23 +18,12 @@ static void my_application_activate(GApplication* application) {
   GtkWindow* window =
       GTK_WINDOW(gtk_application_window_new(GTK_APPLICATION(application)));
 
-  // Use a header bar when running in GNOME as this is the common style used
-  // by applications and is the setup most users will be using (e.g. Ubuntu
-  // desktop).
-  // If running on X and not using GNOME then just use a traditional title bar
-  // in case the window manager does more exotic layout, e.g. tiling.
-  // If running on Wayland assume the header bar will work (may need changing
-  // if future cases occur).
-  gboolean use_header_bar = TRUE;
-#ifdef GDK_WINDOWING_X11
-  GdkScreen* screen = gtk_window_get_screen(window);
-  if (GDK_IS_X11_SCREEN(screen)) {
-    const gchar* wm_name = gdk_x11_screen_get_window_manager_name(screen);
-    if (g_strcmp0(wm_name, "GNOME Shell") != 0) {
-      use_header_bar = FALSE;
-    }
+  // Default to traditional titlebar. Set GTK_CSD=1 to use a header bar.
+  gboolean use_header_bar = FALSE;
+  const gchar* gtk_csd = g_getenv("GTK_CSD");
+  if (gtk_csd != nullptr && g_strcmp0(gtk_csd, "1") == 0) {
+    use_header_bar = TRUE;
   }
-#endif
   if (use_header_bar) {
     GtkHeaderBar* header_bar = GTK_HEADER_BAR(gtk_header_bar_new());
     gtk_widget_show(GTK_WIDGET(header_bar));