x11 backend: set window title

This makes windows identifiable in the window list

backend/x11/backend.c

@@ -221,11 +221,21 @@ static bool wlr_x11_backend_start(struct wlr_backend *backend) {
 
 	init_atom(x11, &x11->atoms.wm_protocols, 1, "WM_PROTOCOLS");
 	init_atom(x11, &x11->atoms.wm_delete_window, 0, "WM_DELETE_WINDOW");
+	init_atom(x11, &x11->atoms.net_wm_name, 1, "_NET_WM_NAME");
+	init_atom(x11, &x11->atoms.utf8_string, 0, "UTF8_STRING");
 
 	xcb_change_property(x11->xcb_conn, XCB_PROP_MODE_REPLACE, output->win,
 		x11->atoms.wm_protocols.reply->atom, XCB_ATOM_ATOM, 32, 1,
 		&x11->atoms.wm_delete_window.reply->atom);
 
+	char title[32];
+	if (snprintf(title, sizeof(title), "wlroots - %s", output->wlr_output.name)) {
+		xcb_change_property(x11->xcb_conn, XCB_PROP_MODE_REPLACE, output->win,
+			x11->atoms.net_wm_name.reply->atom,
+			x11->atoms.utf8_string.reply->atom, 8,
+			strlen(title), title);
+	}
+
 	xcb_map_window(x11->xcb_conn, output->win);
 	xcb_flush(x11->xcb_conn);
 	wlr_output_update_enabled(&output->wlr_output, true);

include/backend/x11.h

@@ -46,6 +46,8 @@ struct wlr_x11_backend {
 	struct {
 		struct wlr_x11_atom wm_protocols;
 		struct wlr_x11_atom wm_delete_window;
+		struct wlr_x11_atom net_wm_name;
+		struct wlr_x11_atom utf8_string;
 	} atoms;
 
 	// The time we last received an event