Old news first, XNA C1 (OpenC1) blog was updated lately with a cool video depicting newly supported/updated features.
If you never heard about ENB series it is a DX9 hook which enables postprocessing effects such as bloom and occlusion. Combined to glide wrapper dgVoodoo it's possible to use it with C2. A pack is available at Road Reaction (under PC Tools) including configs by ChevyII, Hazardic and myself.
Our very Harmalarm made a new beta of his awesome mod available. Now including DD1 cars and tracks! Topic here.
The banger racing version of General Lee was updated to fit properly within the genre. Destined to SOD gamers, but will spread havoc within C2 all the same free of charge! Topic.
The Hawk II (from Splat Pack) was ported to C2. Using Reg materials to keep the unfiltered and full lit C1 rendering. Don't miss the readme. Topic.
[edit] Also keep an eye on the next XnView version. I've been in contact with the author to improve the BRender PIX format support. Things will be better in the next release thus. [/edit]
