Apparently, Creative has a patent on Carmack's Reverse, and they successfully forced Id to modify their techniques for the source drop, as well as to include EAX in Doom 3.

But Carmack's Reverse is discussed quite often and apparently it's a good choice for deferred shading, so it's presumably used in a lot of other high-budget productions too.

Even though it's unlikely that Creative would go after smaller companies, I'm wondering how the bigger studios get around this problem. Do they just cross their fingers and hope Creative doesn't troll them, or do they just not use Carmack's Reverse at all?

  • \$\begingroup\$ I don't really see how caramack's reverse ties into deferred shading really. It's a shadow volume technique to avoid bad things happening when the camera is in shadow. Also I don't think many companies use volume shadow techniques and therefore won't need to worry about the patent issue. If they do, most likely they just get a license to use it like with anything else patented. \$\endgroup\$ Jun 12, 2012 at 9:46
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    \$\begingroup\$ Also, looks like Carmack changed the offending code to not infringe on the patent in the GPL version of Doom 3 (which you should be able to look up). \$\endgroup\$
    – mrbinary
    Jun 12, 2012 at 9:53
  • \$\begingroup\$ @mrbinary They only ended up doing that before the source was released, from what I've read. Before that, Creative just threatened them into including EAX in Doom 3 for their own PR's sake, apparently. \$\endgroup\$ Jun 12, 2012 at 11:18

1 Answer 1


I'm wondering how the bigger studios get around this problem.

They get around it by not using stencil shadow volumes. It's really not a good technique, and it doesn't work very well with deferred rendering, which is the direction a lot of the industry is going in.

Yes, it's nice in that it's pixel accurate, unlike shadow maps. But the many downsides (performance among them) make it a less than attractive idea for game developers.


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