
20.5 Bump Maps 917
Figure 20.13 The normal map for the bricks texture. This map was generated by the CreateNor-
malMap
tool.
is usually just called the tangent and the second vector is called the bitangent.
1
It is
important that the tangent and bitangent vary as smoothly as possible. For a surface
with the topolog y of a square, this is always possible. For a surface with the topology
of a sphere, it is impossible to guarantee global continuity.
2
If we can compute a
tangent T, the bitangent is computed using a cross product, B = N
.
T. The ordered
set {T, B, N} is a right-handed orthonormal set.
The negative of the light direction vector at the surface