-Cube map texture, consisting of six square faces. All of the faces must be of
-the same size. A cube map texture is addressed by three-dimensional texture
-coordinates, with a principal range of [-1, 1]. The face is first selected
-according to the largest coordinate, and the remaining two coordinates are used
-to sample the face image. The images are oriented so that the cross product of
-the s and t axes will point into the cube.