Ensure gtk apps only run on X11

dialog-gtk3/src/main.rs

@@ -77,6 +77,14 @@ fn main() -> anyhow::Result<()> {
     init_logging("BSCREENSAVER_DIALOG_GTK3_LOG");
     glib::log_set_default_handler(glib::rust_log_handler);
 
+    // Can't use the rust version as it requires gtk_init() to be
+    // called first, but the underlying C function requires that
+    // it hasn't.
+    let backends = CString::new("x11").unwrap();
+    unsafe {
+        gtk::gdk::ffi::gdk_set_allowed_backends(backends.as_ptr());
+    };
+
     let config = Configuration::load()?;
     let new_login_command =
         if config.new_login_command == NewLoginCommand::Disabled {

settings/src/main.rs

@@ -1,7 +1,7 @@
 use gtk::{glib, prelude::*};
 use glib::clone;
 use log::warn;
-use std::{env, process::exit, time::Duration};
+use std::{env, process::exit, time::Duration, ffi::CString};
 
 use bscreensaver_util::{init_logging, settings::Configuration, desktop::NewLoginCommand};
 
@@ -18,6 +18,14 @@ fn main() -> anyhow::Result<()> {
     init_logging("BSCREENSAVER_SETTINGS");
     let config = Configuration::load()?;
 
+    // Can't use the rust version as it requires gtk_init() to be
+    // called first, but the underlying C function requires that
+    // it hasn't.
+    let backends = CString::new("x11").unwrap();
+    unsafe {
+        gtk::gdk::ffi::gdk_set_allowed_backends(backends.as_ptr());
+    };
+
     let app = gtk::Application::builder()
         .application_id("org.spurint.bscreensaver-settings")
         .build();