the local expert on shadow casting is Shawn Swift. He has put together a fully featured Shadow System available for purchase for use in your games. See here:
http://www.blitzbasic.com/logs/userlog.php?user=963
Also, shadows have been discussed pretty thoroughly, here are some threads you might want to read:
http://www.blitzbasic.com/bbs/posts.php?topic=21055
"A really easy way to do real-time shadows that is applicable for actual game use"
"Update for my shadow system coming soon."
http://www.blitzbasic.com/bbs/posts.php?topic=21283
"Major shadow rendering techniques"
http://www.blitzbasic.com/bbs/posts.php?topic=20372
I hope that helps! ^_^
http://www.blitzbasic.com/logs/userlog.php?user=963
Also, shadows have been discussed pretty thoroughly, here are some threads you might want to read:
http://www.blitzbasic.com/bbs/posts.php?topic=21055
"A really easy way to do real-time shadows that is applicable for actual game use"
"Update for my shadow system coming soon."
http://www.blitzbasic.com/bbs/posts.php?topic=21283
"Major shadow rendering techniques"
http://www.blitzbasic.com/bbs/posts.php?topic=20372
I hope that helps! ^_^