From a0710d941f653944ac04aeefa4b56160a8f29969 Mon Sep 17 00:00:00 2001
From: Alastair Hughes <hobbitalastair@gmail.com>
Date: Sat, 23 Apr 2016 07:54:05 +1200
Subject: [PATCH] Added an error message if the display can't be opened

---
 demo/x11/main.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/demo/x11/main.c b/demo/x11/main.c
index f58bb2e..46426ed 100644
--- a/demo/x11/main.c
+++ b/demo/x11/main.c
@@ -87,6 +87,8 @@ main(void)
     /* X11 */
     memset(&xw, 0, sizeof xw);
     xw.dpy = XOpenDisplay(NULL);
+    if (!xw.dpy) die("Could not open a display; perhaps $DISPLAY is not set?");
+
     xw.root = DefaultRootWindow(xw.dpy);
     xw.screen = XDefaultScreen(xw.dpy);
     xw.vis = XDefaultVisual(xw.dpy, xw.screen);