The Check for Occlusion routine checks to see whether a virtual
    display is covered (occluded) by another virtual display.

    Format

      SMG$CHECK_FOR_OCCLUSION  display-id ,pasteboard-id

                               ,occlusion-state

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

    Specifies the virtual display to be checked. The display-id
    argument is the address of an unsigned longword that contains
    the display identifier.

    The display identifier is returned by SMG$CREATE_VIRTUAL_DISPLAY.

 pasteboard-id

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

    Specifies the pasteboard to be checked. The pasteboard-id
    argument is the address of an unsigned longword that contains
    the pasteboard identifier.

    The pasteboard identifier is returned by SMG$CREATE_PASTEBOARD.

 occlusion-state

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

    Receives the value denoting whether the display is occluded. The
    occlusion-state argument is the address of a signed longword into
    which the occlusion state is written. Occlusion-state is set to
    1 if the display is occluded or set to 0 if the display is not
    occluded on the specified pasteboard. If the procedure does not
    return SS$_NORMAL, the contents of occlusion-state are undefined.