is available through the Roughness input on the Diffuse BSDF.
http://wiki.blender.org/index.php/Doc:2.6/Manual/Render/Cycles/Nodes/Shaders#Diffuse
Patch by Yasuhiro Fujii, thanks!
modifications and build instructions will follow later.
Cycles uses code from some great open source projects, many thanks them:
* BVH building and traversal code from NVidia's "Understanding the Efficiency of Ray Traversal on GPUs":
http://code.google.com/p/understanding-the-efficiency-of-ray-traversal-on-gpus/
* Open Shading Language for a large part of the shading system:
http://code.google.com/p/openshadinglanguage/
* Blender for procedural textures and a few other nodes.
* Approximate Catmull Clark subdivision from NVidia Mesh tools:
http://code.google.com/p/nvidia-mesh-tools/
* Sobol direction vectors from:
http://web.maths.unsw.edu.au/~fkuo/sobol/
* Film response functions from:
http://www.cs.columbia.edu/CAVE/software/softlib/dorf.php