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?