Chief id Software technomancer John Carmack is now writing new Doom 3 code to dodge legal issues surrounding the rendering technique which gave Doom 3 its lovely shadows, so the engine can be open-sourced.
Before it could release an open-source version of the Doom 3 engine code to all, id Software had to run it by the lawyers. But, their fierce eyes have spotted a slight problem. Chief id technomancer John Carmack is now writing new code to dodge legal issues surrounding the rendering technique, "Carmack's Reverse," which gave Doom 3 its lovely shadows.
"Lawyers are still skittish about the patent issue around 'Carmack's Reverse,' so I am going to write some new code for the Doom 3 release," he explained on Twitter yesterday.
Carmack has been saying for a while, most recently at at QuakeCon, that id would open-source the engine following the release of Rage, and pending legal approval.
"Carmack's Reverse" is a stencil shadowing technique invented independently by several people, including Carmack, but ultimately patented by Creative Labs. While id struck a deal to use it in Doom 3 without paying Creative, evidently the lawyers would err towards a safer, less potentially litigious solution.
Carmack mentioned back in 2004 that, if a deal hadn't been struck with Creative, "We were prepared to use a two-pass algorithm that gave equivalent results at a speed hit." Given how much faster today's computers are than those from 2004, that approach would certainly be less unattractive nowadays. Or perhaps Carmack has brewed up some fancy new rendering tricks over the past seven years.
Wikipedia has more technical details on the Reverse, if that's your bag.