Creative pushes enforcement on Carmack's reverse
 

As I stumbled through the caffeine and sleep deprivation-induced haze at Quakecon, a tortured soul clandestinely whispered to me that Creative is actively working to exploit its patent on the "Carmack's reverse" rending technique used in DOOM 3. Word has it Creative has sent letters to at least eight other game developers about the issue. More may be on the way, because id Software has already licensed DOOM 3 technology to loads more development teams.

http://techreport.com/onearticle.x/7202