.\"	$NetBSD: curses_screen.3,v 1.23.4.1 2018/10/04 10:20:12 martin Exp $
.\"
.\" Copyright (c) 2002
.\"	Brett Lymn (blymn@NetBSD.org, brett_lymn@yahoo.com.au)
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.\" This code is donated to the NetBSD Foundation by the Author.
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.Dd October 2, 2018
.Dt CURSES_SCREEN 3
.Os
.Sh NAME
.Nm curses_screen ,
.Nm filter ,
.Nm ripoffline ,
.Nm use_env ,
.Nm newterm ,
.Nm set_term ,
.Nm delscreen ,
.Nm endwin ,
.Nm initscr ,
.Nm isendwin ,
.Nm is_term_resized ,
.Nm resize_term ,
.Nm resizeterm ,
.Nm setterm ,
.Nm set_tabsize
.Nd curses terminal and screen routines
.Sh LIBRARY
.Lb libcurses
.Sh SYNOPSIS
.In curses.h
.Ft void
.Fn filter "void"
.Ft int
.Fn ripoffline "int line" "int (*init)(WINDOW *win, int cols)"
.Ft void
.Fn use_env "bool value"
.Ft SCREEN *
.Fn newterm "char *type" "FILE *outfd" "FILE *infd"
.Ft SCREEN *
.Fn set_term "SCREEN *screen"
.Ft void
.Fn delscreen "SCREEN *screen"
.Ft int
.Fn endwin "void"
.Ft WINDOW *
.Fn initscr "void"
.Ft bool
.Fn isendwin "void"
.Ft bool
.Fn is_term_resized "int lines" "int cols"
.Ft int
.Fn resize_term "int lines" "int cols"
.Ft int
.Fn resizeterm "int lines" "int cols"
.Ft int
.Fn setterm "char *name"
.Ft int
.Fn set_tabsize "int value"
.Pp
.Va extern int LINES ;
.Pp
.Va extern int COLS ;
.Sh DESCRIPTION
These functions initialize terminals and screens.
.Pp
The
.Fn newterm
function initialises the curses data structures and pointers ready for
use by curses.
The
.Fa type
argument points to a
.Xr terminfo 5
entry, or it may be
.Dv NULL
in which case the TERM environment variable is used.
The
.Fa outfd
and
.Fa infd
are the output and input file descriptors for the terminal.
The
.Fn newterm
function must only be called once  per terminal.
.Pp
The
.Fn set_term
function can be used to switch between the screens defined by calling
.Fn newterm ,
a pointer to the previous screen structure that was in use will be
returned on success.
.Pp
Calling
.Fn delscreen
will destroy the given screen and free all allocated resources.
.Pp
Calling
.Fn endwin
will end the curses session and restore the saved terminal settings.
.Pp
The curses session must be initialised by calling
.Fn initscr
which saves the current terminal state and sets up the terminal and
internal data structures to support the curses application.
This
function call must be, with few exceptions, the first Curses library
call made.
The exception to this rule is the
.Fn newterm
call which may be called prior to
.Fn initscr .
The size of the curses screen is determined by checking the
.Xr tty 4
size and then the
.Xr terminfo 5
entries for the terminal type.
If the environment variables
.Ev LINES
or
.Ev COLUMNS
are set, then these will be used instead.
.Pp
When either
.Fn newterm
or
.Fn initscr
are called, the Curses library sets up signal handlers for
.Dv SIGTSTP
and
.Dv SIGWINCH .
If a signal handler is already installed for
.Dv SIGWINCH ,
this will also be called when the Curses library handler is called.
.Pp
The
.Fn isendwin
function can be used to determine whether or not a refresh of the
screen has occurred since the last call to
.Fn endwin .
.Pp
The size of the screen may be changed by calling
.Fn resize_term
with the updated number of lines and columns.
This will resize the curses internal data structures to accommodate the
changed terminal geometry.
The
.Dv curscr
and
.Dv stdscr
windows and any of their subwindows will be resized to fit the new
screen size.
The application must redraw the screen after a call to
.Fn resize_term .
The
.Fn resizeterm
function is a wrapper for
.Fn resize_term
and adjusts other structure data that handles window dimensions.
The
.Fn is_term_resized
function tests if either of the above functions need to be called.
.Pp
The
.Fn setterm
function sets the terminal type for the current screen to the one
passed, initialising all the curses internal data structures with
information related to the named terminal.
The
.Fa name
argument must be a valid name or alias in the
.Xr terminfo 5
database for this function to succeed.
.Pp
The
.Fn filter
function changes the way the terminal is initialised.
A subsequent call to
.Fn initscr
or
.Fn newterm
performs the following additonal actions:
.Bl -bullet -compact
.It
Disable use of clear, cud, cud1, cup, cuu, cuu1 and vpa.
.It
Set the value of the home string to the value of the cr string.
.It
Set lines equal to 1.
.El
.Pp
The
.Fn ripoffline
function will rip a line from
.Dv stdscr
at the top if
.Fa line
is positive, or at the bottom if negative.
When
.Fn initscr
or
.Fn newterm
is called, a window will be created for each line ripped and passed
to the
.Fa init
function pointer alongwith the number of columns in the window.
This init function cannot use the
.Dv LINES
or
.Dv COLS
variables and cannot call
.Xr wrefresh 3
or
.Xr doupdate 3 ,
but may call
.Xr wnoutrefresh 3 .
.Fn ripoffline
can be called up to five times.
.Pp
The
.Fn use_env
function determines whether the environment variables
.Ev LINES
and
.Ev COLUMNS
override the normal values.
The default is true.
Any call to
.Fn use_env
must precede calls to
.Fn initscr ,
.Fn newterm ,
or
.Fn setupterm .
.Pp
The
.Fn set_tabsize
function will set
.Va TABSIZE
of the current screen to
.Va tabsize .
.Sh RETURN VALUES
Functions returning pointers will return
.Dv NULL
if an error is detected.
The functions that return an int will return one of the following
values:
.Pp
.Bl -tag -width ERR -compact
.It Er OK
The function completed successfully.
.It Er ERR
An error occurred in the function.
.El
.Sh SEE ALSO
.Xr curses_window 3 ,
.Xr tty 4 ,
.Xr terminfo 5 ,
.Xr signal 7
.Sh STANDARDS
The
.Nx
Curses library complies with the X/Open Curses specification, part of the
Single Unix Specification.
.Sh HISTORY
The Curses package appeared in
.Bx 4.0 .
The
.Fn resizeterm
function is a
.Em ncurses
extension to the Curses library and was added in
.Nx 1.6 .
The
.Fn is_term_resized ,
.Fn resize_term
and
.Fn set_tabsize
functions are
.Em ncurses
extension to the Curses library and was added in
.Nx 8.0 .
.Sh BUGS
There is currently an issue with cursor movement in a 1 line sized window
which causes the screen to scroll up.
This can obviously be seen when using
.Fn ripoffline .