When operating in ViewText Mode, UIPACK by default maintains a small (3 line)
scroll region at the base of the terminal screen for prompts and for normal
FORTRAN output. However this region
is erased each time a text Viewport is updated (this being a consequence of the
VAX/VMS Screen Managment Package) so that multiple viewport operations are
relatively inefficient. The Application Programmer may set this scroll region
size to zero, thus inhibiting its update, but having the side-effect that normal
FORTRAN output to the screen may corrupt the screen image.
Normally any Text Viewports defined by the User are prevented by UIPACK from
extending into this scroll region, but by setting the scroll region size to
zero this prevention may be bypassed. Note however, that later setting a
non-zero scroll region will cause this portion of any Viewports to be
obscured by the scroll region. Note also that it is the Application Programmers
responsibility to ensure that the Viewport for input prompts and echoing is
not obscured.
In ViewCursor Mode of operation, the Scroll Region is always set to be zero
and an error will be reported if an attempt is made to make it non-zero.