SYNOPSIS:
    FILTB_NLG sx sy sz sw [fx] [fy] [fz]

DESCRIPTION:
    Do a nonlinear gaussian filtering into the backbuffer (B).

SEE ALSO:
    FILTB_NLC, FILTB_NLC2, FILTB_NLD, NLGS,
    backingstore, COPY_BACKTOGREY, XCHG_GREYANDBACK, ERASE_BACK
