What is Eye vector and half vector? // calculate half angle vector float3 eyeVec = float3(0.0, 0.0, 1.0); float3 halfVec = normalize(lightVec + eyeVec);

The eye vector (also named camera vector) is a synonyme for the position of a virtual observer. (However, in your post above it is the vector from a point on a surface to the observer.)

A "halfway vector" (if you mean that by "half vector") is the unit vector at the half angle between two other vectors. Normally the halfway vector occurs in an alternative formulation of Phong's illumination model, where it is computed between the vector to the viewer v and the light source l:
h := ( v + l ) / || v + l ||

[Edited by - haegarr on November 26, 2005 9:57:59 AM]