.\" Copyright (c) 1980 Regents of the University of California.
.\" All rights reserved.  The Berkeley software License Agreement
.\" specifies the terms and conditions for redistribution.
.\"
.\"	@(#)intro.3	6.1 (Berkeley) 4/23/86
.\"
.sh 1 Usage
.pp
This is a description of how to actually use the screen package.
In it, we assume all updating, reading, etc.
is applied to
.Vn stdscr .
All instructions will work on any window,
with changing the function name and parameters as mentioned above.
.sh 2 "Starting up"
.pp
In order to use the screen package,
the routines must know about terminal characteristics,
and the space for
.Vn curscr
and
.Vn stdscr
must be allocated.
These functions are performed by
.Fn initscr .
Since it must allocate space for the windows,
it can overflow core when attempting to do so.
On this rather rare occasion,
.Fn initscr
returns ERR.
.Fn initscr
must
.bi always
be called before any of the routines which affect windows are used.
If it is not,
the program will core dump as soon as either
.Vn curscr
or
.Vn stdscr
are referenced.
However, it is usually best to wait to call it
until after you are sure you will need it,
like after checking for startup errors.
Terminal status changing routines
like
.Fn nl
and
.Fn cbreak
should be called after
.Fn initscr .
.pp
Now that the screen windows have been allocated,
you can set them up for the run.
If you want to, say, allow the window to scroll,
use
.Fn scrollok .
If you want the cursor to be left after the last change, use
.Fn leaveok .
If this isn't done,
.Fn refresh
will move the cursor to the window's current \*y after updating it.
New windows of your own can be created, too, by using the functions
.Fn newwin
and
.Fn subwin .
.Fn delwin
will allow you to get rid of old windows.
If you wish to change the official size of the terminal by hand,
just set the variables
.Vn LINES
and
.Vn COLS
to be what you want,
and then call
.Fn initscr .
This is best done before,
but can be done either before or after,
the first call to
.Fn initscr ,
as it will always delete any existing
.Vn stdscr
and/or
.Vn curscr
before creating new ones.
.pp
.sh 2 "The Nitty-Gritty"
.sh 3 Output
.pp
Now that we have set things up,
we will want to actually update the terminal.
The basic functions
used to change what will go on a window are
.Fn addch
and
.Fn move .
.Fn addch
adds a character at the current \*y,
returning ERR if it would cause the window to illegally scroll,
.i i.e. ,
printing a character in the lower right-hand corner
of a terminal which automatically scrolls
if scrolling is not allowed.
.Fn move
changes the current \*y to whatever you want them to be.
It returns ERR if you try to move off the window when scrolling is not allowed.
As mentioned above, you can combine the two into
.Fn mvaddch
to do both things in one fell swoop.
.pp
The other output functions,
such as
.Fn addstr
and
.Fn printw ,
all call
.Fn addch
to add characters to the window.
.pp
After you have put on the window what you want there,
when you want the portion of the terminal covered by the window
to be made to look like it,
you must call
.Fn refresh .
In order to optimize finding changes,
.Fn refresh
assumes that any part of the window not changed
since the last
.Fn refresh
of that window has not been changed on the terminal,
.i i.e. ,
that you have not refreshed a portion of the terminal
with an overlapping window.
If this is not the case,
the routines
.Fn touchwin ,
.Fn touchline ,
and
.Fn touchoverlap
are provided to make it look like a desired part of window has been changed,
thus forcing
.Fn refresh
check that whole subsection of the terminal for changes.
.pp
If you call
.Fn wrefresh
with
.Vn curscr ,
it will make the screen look like
.Vn curscr
thinks it looks like.
This is useful for implementing a command
which would redraw the screen in case it get messed up.
.sh 3 Input
.pp
Input is essentially a mirror image of output.
The complementary function to
.Fn addch
is
.Fn getch
which,
if echo is set,
will call
.Fn addch
to echo the character.
Since the screen package needs to know what is on the terminal at all times,
if characters are to be echoed,
the tty must be in raw or cbreak mode.
If it is not,
.Fn getch
sets it to be cbreak,
and then reads in the character.
.sh 3 Miscellaneous
.pp
All sorts of fun functions exists for maintaining and changing information
about the windows.
For the most part,
the descriptions in section 5.4. should suffice.
.sh 2 "Finishing up"
.pp
In order to do certain optimizations,
and,
on some terminals,
to work at all,
some things must be done
before the screen routines start up.
These functions are performed in
.Fn getttmode
and
.Fn setterm ,
which are called by
.Fn initscr .
In order to clean up after the routines,
the routine
.Fn endwin
is provided.
It restores tty modes to what they were
when
.Fn initscr
was first called.
Thus,
anytime after the call to initscr,
.Fn endwin
should be called before exiting.
