The ilActiveMipmap function sets the active mipmap level.

Number

Mipmap level to select as current.

ilActiveMipmap sets a mipmap of the image as the current mipmap. Currently, the only way to generate mipmaps is by calling iluBuildMipmaps. If neither function has been called for the current image, no mipmaps exist for it. If Number is 0, then the current base image is set.

IL_ILLEGAL_OPERATION - IL_ILLEGAL_OPERATION - There is currently no image bound. Use ilGenImages and ilBindImage before calling this function, or Number is too high.
IL_INTERNAL_ERROR - *Big* problem with DevIL. E-mail Denton with the conditions leading up to the error and pray. =]

ilGenImages, ilBindImage, ilActiveImage, ilActiveLayer, iluBuildMipmaps