.\" $OpenBSD: curs_pad.3,v 1.10 2023/10/17 09:52:08 nicm Exp $
.\"
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.\" Copyright 2018-2022,2023 Thomas E. Dickey                                *
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.\" $Id: curs_pad.3,v 1.10 2023/10/17 09:52:08 nicm Exp $
.de bP
.ie n  .IP \(bu 4
.el    .IP \(bu 2
..
.TH curs_pad 3 2023-07-01 "ncurses 6.4" "Library calls"
.na
.hy 0
.SH NAME
\fBnewpad\fP,
\fBsubpad\fP,
\fBprefresh\fP,
\fBpnoutrefresh\fP,
\fBpechochar\fP,
\fBpecho_wchar\fP \- create and display \fBcurses\fP pads
.ad
.hy
.SH SYNOPSIS
\fB#include <curses.h>\fP
.sp
\fBWINDOW *newpad(int \fInlines\fB, int \fIncols\fB);\fR
.br
\fBWINDOW *subpad(WINDOW *\fIorig\fB, int \fInlines\fB, int \fIncols\fB,\fR
      \fBint \fIbegin_y\fB, int \fIbegin_x\fB);\fR
.br
\fBint prefresh(WINDOW *\fIpad\fB, int \fIpminrow\fB, int \fIpmincol\fB,\fR
      \fBint \fIsminrow\fB, int \fIsmincol\fB, int \fIsmaxrow\fB, int \fIsmaxcol\fB);\fR
.br
\fBint pnoutrefresh(WINDOW *\fIpad\fB, int \fIpminrow\fB, int \fIpmincol\fB,\fR
      \fBint \fIsminrow\fB, int \fIsmincol\fB, int \fIsmaxrow\fB, int \fIsmaxcol\fB);\fR
.br
\fBint pechochar(WINDOW *\fIpad\fB, chtype \fIch\fB);\fR
.br
\fBint pecho_wchar(WINDOW *\fIpad\fB, const cchar_t *\fIwch\fB);\fR
.SH DESCRIPTION
.SS newpad
The \fBnewpad\fP routine creates and returns a pointer to a new pad data
structure with the given number of lines, \fInlines\fP, and columns,
\fIncols\fP.
A pad is like a window, except that it is not restricted by the
screen size, and is not necessarily associated with a particular part of the
screen.
Pads can be used when a large window is needed, and only a part of the
window will be on the screen at one time.
Automatic refreshes of pads
(e.g., from scrolling or echoing of input) do not occur.
.PP
It is not
legal to call \fBwrefresh\fP with a \fIpad\fP as an argument; the routines
\fBprefresh\fP or \fBpnoutrefresh\fP should be called instead.
Note that these
routines require additional parameters to specify the part of the pad to be
displayed and the location on the screen to be used for the display.
.SS subpad
The \fBsubpad\fP routine creates and returns a pointer to a subwindow within a
pad with the given number of lines, \fInlines\fP, and columns, \fIncols\fP.
Unlike \fBsubwin\fP, which uses screen coordinates, the window is at position
(\fIbegin\fR_\fIx\fB,\fR \fIbegin\fR_\fIy\fR) on the pad.
The window is
made in the middle of the window \fIorig\fP, so that changes made to one window
affect both windows.
During the use of this routine, it will often be
necessary to call \fBtouchwin\fP or \fBtouchline\fP on \fIorig\fP before
calling \fBprefresh\fP.
.SS prefresh, pnoutrefresh
The \fBprefresh\fP and \fBpnoutrefresh\fP routines are analogous to
\fBwrefresh\fP and \fBwnoutrefresh\fP except that they relate to pads instead
of windows.
The additional parameters are needed to indicate what part of the
pad and screen are involved.
.bP
The \fIpminrow\fP and \fIpmincol\fP parameters specify the upper
left-hand corner of the rectangle to be displayed in the pad.
.bP
The \fIsminrow\fP,
\fIsmincol\fP, \fIsmaxrow\fP, and \fIsmaxcol\fP
parameters specify the edges of the
rectangle to be displayed on the screen.
.PP
The lower right-hand corner of the
rectangle to be displayed in the pad is calculated from the screen coordinates,
since the rectangles must be the same size.
Both rectangles must be entirely
contained within their respective structures.
Negative values of
\fIpminrow\fP, \fIpmincol\fP, \fIsminrow\fP, or \fIsmincol\fP are treated as if
they were zero.
.SS pechochar
The \fBpechochar\fP routine is functionally equivalent to a call to \fBaddch\fP
followed by a call to \fBrefresh\fP(3),
a call to \fBwaddch\fP followed by a call
to \fBwrefresh\fP, or a call to \fBwaddch\fP followed by a call to
\fBprefresh\fP.
The knowledge that only a single character is being output is
taken into consideration and, for non-control characters, a considerable
performance gain might be seen by using these routines instead of their
equivalents.
In the case of \fBpechochar\fP, the last location of the pad on
the screen is reused for the arguments to \fBprefresh\fP.
.SS pecho_wchar
The \fBpecho_wchar\fP function is the analogous wide-character
form of \fBpechochar\fP.
It outputs one character to a pad and immediately refreshes the pad.
It does this by a call to \fBwadd_wch\fP followed by a call to \fBprefresh\fP.
.SH RETURN VALUE
Routines that return an integer return \fBERR\fP upon failure and \fBOK\fP
(SVr4 only specifies "an integer value other than \fBERR\fP") upon successful
completion.
.PP
Routines that return pointers return \fBNULL\fP on error, and set \fBerrno\fP
to \fBENOMEM\fP.
.PP
X/Open does not define any error conditions.
In this implementation
.RS 3
.TP 5
\fBprefresh\fP and \fBpnoutrefresh\fP
return an error
if the window pointer is null, or
if the window is not really a pad or
if the area to refresh extends off-screen or
if the minimum coordinates are greater than the maximum.
.TP 5
\fBpechochar\fP
returns an error
if the window is not really a pad, and the associated call
to \fBwechochar\fP returns an error.
.TP 5
\fBpecho_wchar\fP
returns an error
if the window is not really a pad, and the associated call
to \fBwecho_wchar\fP returns an error.
.RE
.SH NOTES
Note that \fBpechochar\fP may be a macro.
.SH PORTABILITY
BSD curses has no \fIpad\fP feature.
.PP
SVr2 curses (1986) provided the \fBnewpad\fP and related functions,
documenting them in a single line each.
SVr3 (1987) provided more extensive documentation.
.PP
The documentation does not explain the term \fIpad\fP.
However, the Apollo \fIAegis\fP workstation operating system
supported a graphical \fIpad\fP feature:
.bP
These graphical pads could be much larger than the computer's display.
.bP
The read-only output from a command could be scrolled back to inspect,
and select text from the pad.
.PP
The two uses may be related.
.PP
The XSI Curses standard, Issue 4 describes these functions,
without significant change from the SVr3 documentation.
It describes no error conditions.
The behavior of \fBsubpad\fP if the parent window is not
a pad is undocumented,
and is not checked by the vendor Unix implementations:
.bP
SVr4 curses sets a flag in the \fBWINDOW\fP structure in \fBnewpad\fP
which tells if the window is a \fIpad\fP.
.IP
However, it uses this information only in
\fBwaddch\fP (to decide if it should call \fBwrefresh\fP) and
\fBwscrl\fP (to avoid scrolling a pad),
and does not check in \fBwrefresh\fP to ensure that the pad
is refreshed properly.
.bP
Solaris X/Open Curses checks if a window is a pad in \fBwnoutrefresh\fP,
returning \fBERR\fP in that case.
.IP
However, it only sets the flag for subwindows if the parent window is a pad.
Its \fBnewpad\fP function does not set this information.
Consequently, the check will never fail.
.IP
It makes no comparable check in \fBpnoutrefresh\fP,
though interestingly enough, a comment in the source code
states that the lack of a check was an MKS extension.
.bP
NetBSD 7 curses
sets a flag in the \fBWINDOW\fP structure for \fBnewpad\fP and \fBsubpad\fP,
using this to help with the distinction between \fBwnoutrefresh\fP
and \fBpnoutrefresh\fP.
.IP
It does not check for the case where a subwindow is created in
a pad using \fBsubwin\fP or \fBderwin\fP.
.IP
The \fBdupwin\fP function returns a regular window when duplicating a pad.
Likewise, \fBgetwin\fP always returns a window, even if the saved
data was from a pad.
.PP
This implementation
.bP
sets a flag in the \fBWINDOW\fP structure for \fBnewpad\fP and \fBsubpad\fP,
.bP
allows a \fBsubwin\fP or \fBderwin\fP call to succeed having a pad parent by
forcing the subwindow to be a pad,
.bP
checks in both \fBwnoutrefresh\fP and \fBpnoutrefresh\fP to ensure
that pads and windows are handled distinctly, and
.bP
ensures that \fBdupwin\fP and \fBgetwin\fP treat
pads versus windows consistently.
.SH SEE ALSO
\fBcurses\fP(3),
\fBcurs_refresh\fP(3),
\fBcurs_touch\fP(3),
\fBcurs_addch\fP(3).