man/curs_refresh.3x

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.\" $Id: curs_refresh.3x,v 1.46 2024/04/20 21:20:07 tom Exp $
.TH curs_refresh 3X 2024-04-20 "ncurses @NCURSES_MAJOR@.@NCURSES_MINOR@" "Library calls"
.ie \n(.g \{\
.ds `` \(lq
.ds '' \(rq
.\}
.el \{\
.ie t .ds `` ``
.el   .ds `` ""
.ie t .ds '' ''
.el   .ds '' ""
.\}
.
.de bP
.ie n  .IP \(bu 4
.el    .IP \(bu 2
..
.SH NAME
\fB\%doupdate\fP,
\fB\%redrawwin\fP,
\fB\%refresh\fP,
\fB\%wnoutrefresh\fP,
\fB\%wredrawln\fP,
\fB\%wrefresh\fP \-
refresh \fIcurses\fR windows or lines thereupon
.SH SYNOPSIS
.nf
\fB#include <curses.h>
.PP
\fBint refresh(void);
\fBint wrefresh(WINDOW *\fIwin\fP);
\fBint wnoutrefresh(WINDOW *\fIwin\fP);
\fBint doupdate(void);
.PP
\fBint redrawwin(WINDOW *\fIwin\fP);
\fBint wredrawln(WINDOW *\fIwin\fP, int \fIbeg_line\fP, int \fInum_lines\fP);
.fi
.SH DESCRIPTION
.SS "refresh, wrefresh"
The \fBrefresh\fP and \fBwrefresh\fP routines (or \fBwnoutrefresh\fP and
\fBdoupdate\fP) must be called to get actual output to the terminal,
as other routines merely manipulate data structures.
The routine \fBwrefresh\fP copies
the named window to the \fIphysical screen\fP,
taking into account what is already there to do optimizations.
The \fBrefresh\fP routine is the
same, using \fBstdscr\fP as the default window.
Unless \fBleaveok\fP(3X) has been
enabled, the physical cursor of the terminal is left at the location of the
cursor for that window.
.SS "wnoutrefresh, doupdate"
The \fBwnoutrefresh\fP and \fBdoupdate\fP routines allow multiple updates with
more efficiency than \fBwrefresh\fP alone.
In addition to all the window
structures, \fBcurses\fP keeps two data structures representing the terminal
screen:
.bP
a \fIphysical screen\fP,
describing what is actually on the screen, and
.bP
a \fIvirtual screen\fP,
describing what the programmer wants to have on the screen.
.PP
The routine \fBwrefresh\fP works by
.bP
first calling \fBwnoutrefresh\fP,
which copies the named window to the \fIvirtual screen\fP, and
.bP
then calling \fBdoupdate\fP, which compares
the \fIvirtual screen\fP to the \fIphysical screen\fP
and does the actual update.
.PP
If the programmer wishes to output several windows at once, a series
of calls to \fBwrefresh\fP results in alternating calls to \fBwnoutrefresh\fP
and \fBdoupdate\fP, causing several bursts of output to the screen.
By first
calling \fBwnoutrefresh\fP for each window, it is then possible to call
\fBdoupdate\fP once, resulting in only one burst of output, with fewer total
characters transmitted and less CPU time used.
.PP
If the \fIwin\fP argument to
\fBwrefresh\fP is the \fIphysical screen\fP
(i.e., the global variable \fBcurscr\fP),
the screen is immediately cleared and repainted from scratch.
.PP
The phrase \*(``copies the named window
to the virtual screen\*('' above is ambiguous.
What actually happens is that all \fItouched\fP (changed) lines in the window
are copied to the virtual screen.
This affects programs that use overlapping
windows; it means that if two windows overlap, you can refresh them in either
order and the overlap region will be modified only when it is explicitly
changed.
(But see the section on \fBPORTABILITY\fP below for a warning about
exploiting this behavior.)
.SS "wredrawln, redrawwin"
The \fBwredrawln\fP routine indicates to \fBcurses\fP that some screen lines
are corrupted and should be thrown away before anything is written over them.
It touches the indicated lines (marking them changed).
The routine \fBredrawwin\fP touches the entire window.
.SH RETURN VALUE
These routines return the integer \fBERR\fP upon failure and \fBOK\fP
(SVr4 specifies only
\*(``an integer value other than \fBERR\fP\*('')
upon successful completion.
.PP
X/Open Curses does not specify any error conditions.
In this implementation
.RS 3
.TP 5
\fBwnoutrefresh\fP
returns an error
if the window pointer is null, or
if the window is really a pad.
.TP 5
\fBwredrawln\fP
returns an error
if the associated call to \fBtouchln\fP returns an error.
.RE
.SH NOTES
Note that \fBrefresh\fP and \fBredrawwin\fP may be macros.
.SH PORTABILITY
X/Open Curses, Issue 4 describes these functions.
.PP
Whether \fBwnoutrefresh\fP copies to the virtual screen the entire contents
of a window or just its changed portions has never been well-documented in
historic curses versions (including SVr4).
It might be unwise to rely on
either behavior in programs that might have to be linked with other curses
implementations.
Instead, you can do an explicit \fBtouchwin\fP before the
\fBwnoutrefresh\fP call to guarantee an entire-contents copy anywhere.
.SH SEE ALSO
\fB\%curses\fP(3X),
\fB\%curs_outopts\fP(3X)
\fB\%curs_variables\fP(3X)