Direct Volume Rendering with C language

Hi my name is Giuseppe and i’m a ICT student from Italy.
During my Computer Graphics course my teacher gives me a task with openGL and in particular on Direct Volume Rendering.
I found many articles about it but all the code is written in CG (nVidia Language) and OpenGL Shading Language.
I’m searching for some C or C++ code that make some simple example of Direct Volume Rendering (Volume Ray casting or Splatting or Shear warp).

I hope that you can help me

Thank you!

volvis 1.1 is your best choice ,the souce code is very simple.
Not like VTK,very complicated!
When search volvis 1.1 with google,you will see"Download VolVis 1.1 with MSVC++ 6.0 Source Code - ZIP file, 106KB. Screenshot. "