Geometric meshes often must include surface information for lighting computations.
is defined as surface normal perpendicular to the mesh. Triangular meshes imply a
defined by the winding order of the vertices of the triangles (typically counter-clockwise, although clock-wise winding can also be used). For efficient rendering,
are used for rendering rather than face normals
and a bi-tangent
are gradient direction vectors along the surface of a mesh. Together with the
they describe a full 3-axis coordinate system useful for many advanced lighting techniques.