Sphere tangent seams

Create a sphere in scene and give it a material ShowTangent.
You will see the seams:

ShowTangent Material:

How to get seamless tangent?

Tangents are UV-Map related. You want to get rid of Tangent Seams? Unwrap the Mesh so there are no UV Seams or the UVs have the same orientation

Stock sphere has wrong tangents and binormals at UV seam.

I think the tangent seams which caused by uv seams should just happen at the triangles contain pole, or the longitude 0 and longitude 360.

But in figure 1, the tangent seams is radial.

And if use MikkT to calculate tangent, it should not have seams in longitude 0 and longitude 360.

And how to get no seams tangent?

This is the sphere uv, i’m a programmer, i can’t find the problem.


Can you upload a sphere fbx have correct uv?

The issue is not strictly UE4-specific. If you are letting UE4 recalculate tangents and bitangents, it is incapable of averaging them across UV seams. If however, you are exporting them, it is all about how exporter in question performs that.

It would be indeed nice if Epic implemented proper tangent and bit-tangent re-calculation across UV seams, but on practice, side effects of not doing so are minor to negligible.

A UV Map will NEVER be Continous. You see it at the top and the lower sides. The Triangles are disconnected.

Here you can see how the Tangent changes when the UV Layout changes:




If you want to get rid of Tangent Seams your
UV Seams need to have the same Orientation. Something not possible in a sphere.