With all the 3D frenzy for home entertainment systems going on, ioquake3 did not want to fall behind, so as of the latest SVN revision ioquake3 officially supports rendering of stereoscopic images. Actually, we’re not quite sure whether this works for quad buffer based rendering methods for shutter glasses as we lack the hardware (can someone give us a heads-up on this? Any SGI fanboys here?), but rendering of anaglyph images definitely does.
You need to have red-cyan glasses to view these images in their full glory. As always, the cvars and switches needed to turn on this new functionality can be found in the changes to the README. I have also written up an extensive information page about the techniques behind stereo rendering on ioquake3’s wiki to get you going on stereoscopic ioquake3.