SYNOPSIS:
    FILTB_NLD_POSADD sx sy sz sw [fx] [fy] [fz] [fw]

DESCRIPTION:
    Do nonlinear difference filtering into the backbuffer (B),
    adding the result (amplified by fw) to the original values,
    if the result is positive.
    The nonlinearity is introduced by using sw as a dead zone.

SEE ALSO:
    FILTB_NLC, FILTB_NLG, FILTB_NLD, FILTB_NLD_ADD,
    FILTB_NLD_NEGADD, NLGS,
    backingstore, COPY_BACKTOGREY, XCHG_GREYANDBACK, ERASE_BACK
