How to run Cg vertex/fragment shader on CPU?

I'm playing about with some vertex and fragment shaders using Cg on my little netbook (running Linux). Clearly I'm going to frequently hit resource limits for my graphics controller, so was wondering if there's a nice way to run the shaders on the开发者_JS百科 CPU, just to test them. Something like D3D's refrast...

TIA

Andy

Opensource Opengl software Mesa has shader support : http://www.mesa3d.org/shading.html