From 2dc7f60b59756f1b73c182b33c84c965c3e54f9a Mon Sep 17 00:00:00 2001
From: rkrolib <rkrolib@7f0cb862-5218-0410-a997-914c9d46530a>
Date: Sat, 11 Oct 2003 07:44:02 +0000
Subject: [PATCH] Check the glutDisplayFunc() callback for being a NULL
 pointer.  This is illegal and is disallowed in GLUT 3.0+, so we disallow it
 too in freeglut 2.0.1+

git-svn-id: https://svn.code.sf.net/p/freeglut/code/trunk@221 7f0cb862-5218-0410-a997-914c9d46530a
---
 freeglut/freeglut/src/freeglut_callbacks.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/freeglut/freeglut/src/freeglut_callbacks.c b/freeglut/freeglut/src/freeglut_callbacks.c
index 90baf10..da06283 100644
--- a/freeglut/freeglut/src/freeglut_callbacks.c
+++ b/freeglut/freeglut/src/freeglut_callbacks.c
@@ -48,6 +48,9 @@
  */
 void FGAPIENTRY glutDisplayFunc( void (* callback)( void ) )
 {
+    if( !callback )
+	fgError ("Fatal error in program.  NULL display callback not "
+	    "permitted in GLUT 3.0+ or freeglut 2.0.1+\n");
     SET_CALLBACK( Display );
 
     /*