Another example, probably better explained:
The 3DS Max vertex data is upside down in my engine, and I'm guessing it's because the XYZ values in 3DS Max are left handed, and OpenGL is right handed right?
That's manageable, but the UV data is messed around too, and I noticed that the way I was even going on about mirroring textures is wrong because I was assuming a texture that covers the entire image, not just part of it.
I'm meaning that, in the example above, if I only put some texture color in the Purple area, and I mirror it horizontally with my current code, I'm just picking the UV values that correspond to the Red area in the texture, and that's wrong... I made this assuming 2D images and square textures and now that I'm loading directly from the FBX, it's not working for 3D models.
Using "1.0f - uv" values work for 2D planes, but not for 3D models...