The Scroll a Display Under a Viewport routine scrolls a virtual
    display under its associated viewport.

    Format

      SMG$SCROLL_VIEWPORT  display-id [,direction] [,count]

1  –  Returns

    OpenVMS usage:cond_value
    type:         longword (unsigned)
    access:       write only
    mechanism:    by value

2  –  Arguments

 display-id

    OpenVMS usage:identifier
    type:         longword (unsigned)
    access:       read only
    mechanism:    by reference

    Display identifier of the virtual display to be scrolled. The
    display-id argument is the address of an unsigned longword
    containing this identifier.

 direction

    OpenVMS usage:mask_longword
    type:         longword (unsigned)
    access:       read only
    mechanism:    by reference

    Optional direction specifier. The direction argument is the
    address of a longword bit mask that contains the direction code
    specifying the scrolling direction. The optional count argument
    can be used to specify the number of lines to scroll in the
    specified direction. Valid values for direction are as follows:

    SMG$M_UP       Scroll count lines upward.
    SMG$M_DOWN     Scroll count lines downward.
    SMG$M_RIGHT    Scroll count columns to the right.
    SMG$M_LEFT     Scroll count columns to the left.

    SMG$M_UP is the default.

 count

    OpenVMS usage:longword_signed
    type:         longword (signed)
    access:       read only
    mechanism:    by reference

    Optional number of rows or columns to be scrolled. The default is
    1.