material.tangent

TANGENT

Calculates the tangents for the 3rd texture coordinate set (TEXCOORD2). This way tangents can be used for model or level geometry shaders.

on - third texture coordinate set is the tangent vector.
off - no tangents.

Flag (can only be set in a definition, but not during gameplay)

The binormal vector can be calculated by the vertex shader from the cross product of the vertex normal and the u tangent.
On animated models the tangents have to be recalculated every frame, affecting the frame rate. Use this flag with care.

material mat_bump3
{
   ...
   flags = TANGENT;
   ...
}