Hi,

Can some one tell me, why we calculate Hlaf Vactor while we write any blinn shading model?

The half angle is a short cut that’s used instead of calculating the reflection vector. Jim Blinn came up with this method as an optimization over the Phong lighting model. In the case where you’re using a directional light source, the light vector and camera vector are constant for every pixel in the image and therefore the half angle only has to be calculated once for the entire frame instead of for every pixel. This optimization doesn’t work for point lights though.

In the Phong model, you have to use the surface normal to calculate the reflection vector and so the inputs are different for each pixel.

Does that help to answer your question?

Here’s an article that explains it better than I did:

-Ben

Yes Ben, this is the perfect answer 4 my question.

and thanks for giving reply.

i m just trying to write some hardware shader using FX Composer, before that i just wanted clear some of the basics of shading calculations.

Thanks:jayeshM