Mmmm: http://www.tomshardw...ml#xtor=RSS-181 During DOOM 3's development, Carmack independently discovered and publicized a shading process later dubbed as "Carmack's Reverse," but Creative Labs had already filed for a patent on the technique back in 1999. Carmack said he created a separate shading method that got around the patent issues, but that meant a significant "speed hit" in DOOM 3's performance. Thus, the studio had no choice but to license the "depth fail" patent from Creative and move on. "The Doom 3 GPL source code release does not include functionality enabling rendering of stencil shadows via the 'depth fail' method, a functionality commonly known as 'Carmack's Reverse,'" states the source code notes. So there's the old performance issue Carmack talked about?