The Cg Tutorial: The Definitive Guide to Programmable Real-Time Graphics I will write the shader code with DirectX or OpenGL. The book "The Cg Tutorial" is worthy for me to buy and learn the shader code? I have many books about the shader code in DirectX. But now I will use OpenGL. Cg,GLSL, which is better to write the shader code in OpenGL? Could Somebody suggest me some books of shader using in OpenGL?

My opinion is that The Cg Tutorial is a good book. However, one thing you will find is that a lot of OpenGL code on the internet is done in GLSL. So i would advise you to learn both. It is a valuable skill to know what a GLSL program is doing so you can do it in Cg. Nvidia's SDK has lots of Cg examples too, which will help you to integrate your Cg into OpenGL.

Good Luck

I couldnt help but reply to this i have the Cg Book open by my laptop haha.

I agree, learn GLSL first, then go ahead with Cg.