What parts of the 4x4 Modelview transformation get applied to normals?

[mfr...@gmail.com]

I am capturing data from my OpenGL applications by listening to
function calls on the other side of the OpenGL library. The goal is to
generate 3D model files (ie. .obj) that represent the rendered geometry
in eye/view coordinates. that is, after the Modelview transformation,
but before projection or perspective.

By applying the current 4x4 ModelView matrix to all vertices, I am able
to reconstitute my geometries no problem. But now I am trying to add in
the vertex normals to my output, and have a question:

does the entire 4x4 ModelView matrix get applied to the initial [u,v,w]
values for normals to produce the final [u,v,w] values? it would seem
that since normals are only directional, you might only want to apply
the Rotation (and possibly Scale) components of the ModelView matrix to
the normals.

Any thoughts?

thanks,
mike

[fungus]

mfr...@gmail.com wrote:
>
> does the entire 4x4 ModelView matrix get applied to the initial [u,v,w]
> values for normals to produce the final [u,v,w] values?

No.

> it would seem
> that since normals are only directional, you might only want to apply
> the Rotation (and possibly Scale) components of the ModelView matrix to
> the normals.
>

Correct.

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