Trouble with curses/scrolling: poor visual effect

[Lite Lin]

Hello,
  I have a question regarding the use of the curses library.  I am
working on a semester project, part of it requires a curses based, vi
style viewer.  When the cursor moves beyond the top/bottom of the
screen, I use repeated calls to addstr() to update the whole screen,
that causes quite visible and annoying glitches on the screen.  I am
not using scroll() because that allows me to scroll up the screen but
not the other way.  When vi does scrolling, the visual effect is so
much better, but I do not have access to the source code of vi, and I
do not even know whether vi is based on curses or termcap.
  I would be grateful if someone would kindly tell me what the problem
is and/or suggest a solution.
  Thank you,
	Lite