Oliver McFadden, the developer that wrote the Radeon Revenge reverse-engineering utility, was thinking about writing an open-source BIOS for Radeon GPUs, and brought ioquake3 to the Nokia N900, decided to write a new GL Shading Language (GLSL) renderer back-end for the id Tech 4 engine.
There's already been some GLSL renderers available for Doom 3, but none that had worked on McFadden's i965 hardware nor did they render correctly (or produced pixel errors), so he wrote a new back-end that would work.
McFadden's new GLSL renderer for Doom 3 is working but not yet fully complete. He talks about the work on his blog.
ioDoom3 or any other code-base yet.
what's going on with ioDoom3, there is one GLSL renderer already being worked on in ioDoom3. From its merge request:
This merge request includes a new GLSL backend, which can be used to replace the current ARB2 backend. Should come in handy for many mod teams due to id software not including the actual shader files themeselves in the source archive.However, in terms of commits to the official ioDoom3 Git repository, there's sadly been no commits since last December... The ioDoom3 mailing list has also been light on activity. However, there has been commits to various branches/forks as illustrated on this Gitorious page.
Right now, only the interaction, ambient interaction, and stencil shadow shaders have been rewritten to GLSL. It's definatly not 100% equivalent, since I am not using the normalization cubemap or the specular lookup table, but should be around the same speed wise (if not faster in some areas) and look a lot better.
The heathaze, glass, and environment shaders still need to be done.
I also fixed two-sided stencil shadowing by using the vendor neutral OpenGL 2.0 glStencilOpSeparate functionality and removed the unused nvidia and ati extensions. This gives a nice performance increase in heavily shadowed areas.
There is also another open-source Doom 3 engine fork called DHEWM3 and can be found on GitHub. This code has sadly not been touched since the middle of January.