Thanks for your reply, but I can not understand what you said.
Because, Mr/Ms enn0x (Sun Nov 13, 2011 5:18 am) answered as following
panda3d.org/forums/viewtopic … &start=450
My code just followed the code in the URL.
And more, from the source code;
panda3d.org/reference/1.8.0 … source.php
line 78-81
I can not find the wrong in my code ?