plgvpd: Get viewport limits in normalized
device coordinates 

DESCRIPTION:

    Get viewport limits in normalized device coordinates. 

SYNOPSIS:

plgvpd(p_xmin, p_xmax, p_ymin, p_ymax)

ARGUMENTS:

    p_xmin (PLFLT *, output) :      Lower viewport limit of the normalized
    device coordinate in x. 

    p_xmax (PLFLT *, output) :      Upper viewport limit of the normalized
    device coordinate in x. 

    p_ymin (PLFLT *, output) :      Lower viewport limit of the normalized
    device coordinate in y. 

    p_ymax (PLFLT *, output) :      Upper viewport limit of the normalized
    device coordinate in y.