10.7 Bump Mapped Reflections

To the authors' knowledge, at least one hardware platform available at the time of writing supports a further embellishment to bump mapping: bump mapped reflections.

If the bump map is stored as displacements to the normal ( $\frac{\partial F}{\partial u}$ and $\frac{\partial F}{\partial u}$), rather than a height field, the displacements can be used as offsets added to the texture coordinates used in a second texture. This second texture represents the lighting environment, and can be the environment mapped approximation to phong lighting discussed in Section 10.1.1, or an environment map approximating reflections from the surface as discussed in Section 11.2.1.