When using a tangent space normal texture, the orientation of UV islands affects the normals even when using the Generated or Object Texture Coordinate. How can a UV map influence a texture that is NOT using any UV map ? How can tangent space itself be affected by the UV map ?
Here's the basic setup :
- a plane split in 2 faces, each one being rotated differently in the UV map
- a noise texture with generated mapping.
And here's how it looks :
See how turning one face by 180° in the UV map removes the seam, while the noise texture is using a generated mapping.