man/curs_pad.3x

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.\" $Id: curs_pad.3x,v 1.61 2024/04/27 17:55:43 tom Exp $
.TH curs_pad 3X 2024-04-27 "ncurses @NCURSES_MAJOR@.@NCURSES_MINOR@" "Library calls"
.ie \n(.g \{\
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.de bP
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..
.SH NAME
\fB\%newpad\fP,
\fB\%subpad\fP,
\fB\%prefresh\fP,
\fB\%pnoutrefresh\fP,
\fB\%pechochar\fP,
\fB\%pecho_wchar\fP \-
create and display \fIcurses\fR pads
.SH SYNOPSIS
.nf
\fB#include <curses.h>
.PP
\fBWINDOW *newpad(int \fInlines\fP, int \fIncols\fP);
\fBWINDOW *subpad(WINDOW *\fIparent\fP, int \fInlines\fP, int \fIncols\fP,
      \fBint \fIbegin_y\fB, int \fIbegin_x\fB);\fR
.PP
\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
\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
.PP
\fBint pechochar(WINDOW *\fIpad\fB, chtype \fIch\fB);\fR
\fBint pecho_wchar(WINDOW *\fIpad\fB, const cchar_t *\fIwch\fB);\fR
.fi
.SH DESCRIPTION
A
.I curses
.I 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,
only part of which is to be visible on the screen.
Pads are not automatically refreshed by scrolling or input-echoing
operations.
.PP
Pads cannot be refreshed with \fB\%wrefresh\fP(3X);
use
.B \%prefresh
or
.B \%pnoutrefresh
instead.
.SS newpad
\fB\%newpad\fP creates and returns a pointer to a new pad data structure
with the given number of lines,
.IR nlines ,
and columns,
.IR ncols .
.SS subpad
.B \%subpad
creates and returns a pointer to a subwindow within a pad
with the given number of lines,
.IR nlines ,
and columns,
.IR ncols .
Unlike \fB\%subwin\fP(3X),
which uses screen coordinates,
the new pad is placed at position
.RI ( begin_y ,
.IR begin_x )
relative to its parent.
Thus,
changes made to one pad can affect both.
When operating on a subpad,
it is often necessary to call \fB\%touchwin\fP(3X) or
\fB\%touchline\fP(3X) on
.I parent
before calling
.BR \%prefresh .
.SS "prefresh, pnoutrefresh"
.B \%prefresh\fP
and
.B \%pnoutrefresh
are analogous to \fB\%wrefresh\fP(3X) and \fB\%wnoutrefresh\fP(3X)
except that they operate on pads rather than windows.
They require additional parameters are needed to indicate what portions
of the pad and screen are involved.
.bP
.I pminrow
and
.I pmincol
specify the upper left-hand corner of a rectangular view of the pad.
.bP
.IR sminrow ,
.IR smincol ,
.IR smaxrow ,
and
.I smaxcol
specify the vertices 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.
.I curses
treats
negative values of any of these parameters as zero.
.SS pechochar
.B \%pechochar
is functionally equivalent to calling \fB\%waddch\fP(3X) followed by
.BR \%prefresh .
It suggests to the
.I curses
optimizer that only a single character is being output;
a considerable performance benefit may be thus enjoyed.
The location of the character
.I ch
written to the pad is used to populate the arguments to
.BR \%prefresh .
.SS pecho_wchar
.B \%pecho_wchar\fP
is functionally equivalent to calling \fB\%wadd_wch\fP(3X) followed by
.BR \%prefresh .
It suggests to the
.I curses
optimizer that only a single wide character is being output;
a considerable performance benefit may be thus enjoyed.
The location of the character
.I wch
written to the pad is used to populate the arguments to
.BR \%prefresh .
.SH RETURN VALUE
Functions that return an integer return \fBERR\fP upon failure and
\fBOK\fP
(SVr4 specifies only
\*(``an integer value other than \fBERR\fP\*('')
upon successful completion.
.PP
Functions that return pointers return \fBNULL\fP on error,
and set \fB\%errno\fP to \fB\%ENOMEM\fP.
.PP
X/Open Curses does not specify any error conditions.
In this implementation
.RS 3
.TP 5
\fB\%prefresh\fP and \fB\%pnoutrefresh\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 \fB\%wechochar\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 \fB\%wecho_wchar\fP returns an error.
.RE
.SH NOTES
\fB\%pechochar\fP may be a macro.
.SH PORTABILITY
BSD \fIcurses\fP has no \fIpad\fP feature.
.PP
SVr2 \fIcurses\fP (1986) provided the \fB\%newpad\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
X/Open Curses, Issue 4 describes these functions,
without significant change from the SVr3 documentation.
It describes no error conditions.
The behavior of \fB\%subpad\fP if the parent window is not
a pad is undocumented,
and is not checked by the vendor Unix implementations:
.bP
SVr4 \fIcurses\fP sets a flag in the \fI\%WINDOW\fP structure in
\fB\%newpad\fP which tells if the window is a \fIpad\fP.
.IP
However, it uses this information only in
\fB\%waddch\fP (to decide if it should call \fB\%wrefresh\fP) and
\fB\%wscrl\fP (to avoid scrolling a pad),
and does not check in \fB\%wrefresh\fP to ensure that the pad
is refreshed properly.
.bP
Solaris \fI\%xcurses\fP checks whether a window is a pad in
\fB\%wnoutrefresh\fP,
returning \fBERR\fP in that case.
.IP
However,
it only sets the flag for subwindows if the parent window is a pad.
Its \fB\%newpad\fP function does not set this information.
Consequently, the check will never fail.
.IP
It makes no comparable check in \fB\%pnoutrefresh\fP,
though interestingly enough, a comment in the source code
states that the lack of a check was an MKS extension.
.bP
NetBSD 7 \fIcurses\fP
sets a flag in the \fI\%WINDOW\fP structure
for \fB\%newpad\fP and \fB\%subpad\fP,
using this to help with the distinction between \fB\%wnoutrefresh\fP
and \fB\%pnoutrefresh\fP.
.IP
It does not check for the case where a subwindow is created in
a pad using \fB\%subwin\fP or \fB\%derwin\fP.
.IP
The \fB\%dupwin\fP function returns a regular window when duplicating a pad.
Likewise, \fB\%getwin\fP always returns a window, even if the saved
data was from a pad.
.PP
This implementation
.bP
sets a flag in the \fI\%WINDOW\fP structure
for \fB\%newpad\fP and \fB\%subpad\fP,
.bP
allows a \fB\%subwin\fP or \fB\%derwin\fP call to succeed having a pad parent by
forcing the subwindow to be a pad,
.bP
checks in both \fB\%wnoutrefresh\fP and \fB\%pnoutrefresh\fP to ensure
that pads and windows are handled distinctly, and
.bP
ensures that \fB\%dupwin\fP and \fB\%getwin\fP treat
pads versus windows consistently.
.SH SEE ALSO
\fB\%curses\fP(3X),
\fB\%curs_addch\fP(3X),
\fB\%curs_refresh\fP(3X),
\fB\%curs_touch\fP(3X)