Mesh.tangents

Description

The tangents of the mesh.

Tangents are mostly used in bump-mapped shaders. A tangent is a unit length vector that follows mesh surface along horizontal (U) texture direction. Tangents in Unity are represented as Vector4, with x,y,z components defining the vector, and w used to flip the binormal if needed.

Unity calculates the other surface vector (binormal) by taking a cross product between normal and tangent, and multiplying result by tangent.w. Thus w should always be 1 or -1.

You should calculate tangents yourself if you plan to use bump-mapped shaders on the mesh. Assign tangents after assigning normals or using RecalculateNormals.

Note: To make changes to the tangents it is important to copy the tangents from the Mesh. Once the tangents have been copied and changed the normals can be reassigned back to the Mesh.