5
\$\begingroup\$

I am updating one of my shaders to a version of OpenGL/GLSL that doesn't automatically provide gl_NormalMatrix (for educational purposes; I'm not ripping out working code for the sake of it). Therefore, I need to compute my own normal matrix on the CPU and pass it in.

I understand that a separate normal matrix is used to avoid issues with non-uniform scaling affecting the direction of normals. However, I've noticed that in my code I never perform any scaling let alone a non-uniform one. So, I'm tempted to use the upper left 3x3 sub-matrix for transforming my normals and calling it a day (perhaps normalising them to allow for uniform scaling).

My program assumes that every mesh it loads is already at the correct size, with no scaling required.

Will I soon run into something that requires scaling (uniform or otherwise), or is there another reason for using a separate normal matrix that I haven't realised?

\$\endgroup\$
6
\$\begingroup\$

You're not missing anything.

The normal matrix exists in case the upper-left 3x3 of your regular model-view transformation is unsuitable for transforming normals (that is, contains non-uniform scale or other craziness).

If you know the upper-left 3x3 is always suitable for use in the transformation of normals, there's no reason to bother with a separate "normal matrix."

Most applications of 3D graphics for games can use the upper-left 3x3 just fine. It's broader, more general 3D graphics uses that more often have a need for a distinct normal matrix.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.