NAME
    GetVPModeID -- get the 32 bit DisplayID from a viewport. (v36)

SYNOPSIS
    modeID =  GetVPModeID( vp )
    d0                     a0

    ULONG GetVPModeID( struct viewport *);

FUNCTION
    returns the normal display modeID, if one is currently  associated
    with this viewport.

INPUTS
    vp -- pointer to a viewport structure.

RESULT

    modeID -- a 32 bit DisplayInfoRecord identifier associated with
              this viewport, or invalid_id.

NOTES
    Test the return value of this function against INVALID_ID, not NULL.
    (INVALID_ID is defined in graphics/displayinfo.h).

BUGS

SEE ALSO
    graphics/displayinfo.h, modenotavailable()