diff --git a/rust-polytreewm/src/xbase.rs b/rust-polytreewm/src/xbase.rs
index 8514ae8..eca95f3 100644
--- a/rust-polytreewm/src/xbase.rs
+++ b/rust-polytreewm/src/xbase.rs
@@ -1,18 +1,26 @@
+use crate::geom;
+
 use std::os::raw::*;
 use std::ptr::null;
 
 use x11::xlib::{self, Display};
 
+pub type ErrorHandler =
+    unsafe extern "C" fn(*mut Display, *mut xlib::XErrorEvent) -> c_int;
+
 pub struct Xbase {
     program_title: String,
     x_display: *mut Display,
     x_screen: c_int,
     x_root: c_ulong,
+    screen_sizes: geom::Sizes,
+    x_error: Option<ErrorHandler>,
 }
 
 impl Xbase {
     pub fn new(
         program_title: String,
+        x_error_handler: ErrorHandler,
     ) -> Result<Self, Box<dyn std::error::Error>> {
         unsafe {
             if xlib::XSupportsLocale() == 0 {
@@ -27,12 +35,46 @@ impl Xbase {
             let x_screen = xlib::XDefaultScreen(x_display);
             let x_root = xlib::XRootWindow(x_display, x_screen);
 
+            let screen_sizes = geom::Sizes::new(
+                xlib::XDisplayWidth(x_display, x_screen),
+                xlib::XDisplayHeight(x_display, x_screen),
+            );
+
+            let x_error = xlib::XSetErrorHandler(Some(x_error_wm_check));
+
+            // TODO: XSetErrorHandler
+
+            xlib::XSelectInput(
+                x_display,
+                xlib::XDefaultRootWindow(x_display),
+                xlib::SubstructureRedirectMask,
+            );
+            xlib::XSync(x_display, xlib::False);
+            xlib::XSetErrorHandler(Some(x_error_handler));
+            // TODO: XSetErrorHandler
+            xlib::XSync(x_display, xlib::False);
+
             Ok(Self {
                 program_title,
                 x_display,
                 x_screen,
                 x_root,
+                screen_sizes,
+                x_error,
             })
         }
     }
 }
+
+impl Drop for Xbase {
+    fn drop(&mut self) {
+        unsafe { xlib::XCloseDisplay(self.x_display) };
+    }
+}
+
+unsafe extern "C" fn x_error_wm_check(
+    _display: *mut Display,
+    _x_error_event: *mut xlib::XErrorEvent,
+) -> c_int {
+    panic!("another window manager is already running");
+}