// texture normal {} attribute
// create a texture that has a bumpiness corresponding to color index
// image maps into X-Y plane from <0,0,0> to <1,1,0>
bump_map { // uses image color or index as bumpiness
  png "plasma3.png" // the file to read (iff/tga/gif/png/jpeg/tiff/sys)
  map_type 0        // 0=planar, 1=spherical, 2=cylindrical, 5=torus
  interpolate 2     // 0=none, 1=linear, 2=bilinear, 4=normalized distance
  // once           // for no repetitive tiling
  // [use_color | use_index]
  bump_size 0.5     // 0...3
} // bump_map