--- a/demos/render_nff.py	Thu May 15 19:15:57 2008 +0200
+++ b/demos/render_nff.py	Mon May 19 22:59:04 2008 +0200
@@ -1,8 +1,12 @@
 #!/usr/bin/python
 
-# read nff data from standart input and render image to render_nff.png
-# see http://tog.acm.org/resources/SPD/
-# cylinders are not implemented
+# Usage: render_nff.py [scene.nff] [output.png]
+# reads scene from nff file and render it to PNG file
+# if no output file name is given, it makes one from input name
+# reads from stdin by default
+
+# see http://tog.acm.org/resources/SPD/ for nff format description
+# cylinders are currently not implemented
 
 from pyrit import *
 from math import pi