It's hard to say without seeing the whole project so here are a few ideas:
- Check if you have the project's paths properly set up - maybe a path to some library/header file is missing. Check the other project (the one which works) and compare. Make sure to adjust the paths/settings for the new project's location.
- Are you using the same version of library/ies that in the other project? If not maybe this version doesn't support
GL_TEXTURE_MAX_ANISOTROPY_EXT (I don't know if it should, just looking for possible explanations).
- Make sure you have necessary header file(s) included in the source file where you're trying to use
From what I gather, it seems that anisotropic filtering is still implemented as an extension and isn't included in
OpenGL Core. Therefore you have to use it like any other extension (if you don't know how, there are plenty of tutorials).
As for the value itself, the docs define it as:
#define GL_TEXTURE_MAX_ANISOTROPY_EXT 0x84FE
#define GL_MAX_TEXTURE_MAX_ANISOTROPY_EXT 0x84FF
If you don't want to define it by yourself or if need more
OpenGL extensions you should just use
glext.h or some other library like you used to.