http://frictionalgames.blogspot.co.uk/2010/01/perception-of-000.html http://frictionalgames.blogspot.co.uk/2010/01/perception-of-... There's a reasonable introd

http://frictionalgames.blogspot.co.uk/2010/01/perception-of-000.html http://frictionalgames.blogspot.co.uk/2010/01/perception-of-... There's a reasonable introductory answer