I am studying computer graphics with opengl and d3d and I am looking for a game engine that allows low level tinkering. For example I should be able to implement my own lighting solution.

I tested many engines and I know that I can create my own shaders in unity and udk. I also know that unity offers a good amount of shader access, someone recently implemented voxel based global illumination.

Do you know if the same thing is possible in UDK? I am not sure how far I can go with the material editor.

Maybe there are other quality game engines like unity or udk that allow low level programming?