GitLab

When scrolling down a line, a full refresh of the edit window is only
needed when softwrap is on, because only then the movement is irregular.
When each file line takes up just one screen line (softwrap is off),
edit_scroll() is perfectly able to scroll and redraw only the necessary
lines.

(But... when doing a full refresh anyway with softwrap, why bother
scrolling at all?  Why not just adjust edittop and call refresh?)