curs_pad(3x) Library calls curs_pad(3x)
newpad, subpad, prefresh, pnoutrefresh, pechochar, pecho_wchar - create
and display curses pads
#include <curses.h>
WINDOW *newpad(int nlines, int ncols);
WINDOW *subpad(WINDOW *orig, int nlines, int ncols,
int begin_y, int begin_x);
int prefresh(WINDOW *pad, int pminrow, int pmincol,
int sminrow, int smincol, int smaxrow, int smaxcol);
int pnoutrefresh(WINDOW *pad, int pminrow, int pmincol,
int sminrow, int smincol, int smaxrow, int smaxcol);
int pechochar(WINDOW *pad, chtype ch);
int pecho_wchar(WINDOW *pad, const cchar_t *wch);
The newpad routine creates and returns a pointer to a new pad data
structure with the given number of lines, nlines, and columns, ncols.
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.
It is not legal to call wrefresh with a pad as an argument; the
routines prefresh or pnoutrefresh 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.
The subpad routine creates and returns a pointer to a subwindow within
a pad with the given number of lines, nlines, and columns, ncols.
Unlike subwin, which uses screen coordinates, the window is at position
(begin_x, begin_y) on the pad. The window is made in the middle of the
window orig, so that changes made to one window affect both windows.
During the use of this routine, it will often be necessary to call
touchwin or touchline on orig before calling prefresh.
The prefresh and pnoutrefresh routines are analogous to wrefresh and
wnoutrefresh 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.
o The pminrow and pmincol parameters specify the upper left-hand
corner of the rectangle to be displayed in the pad.
o The sminrow, smincol, smaxrow, and smaxcol parameters specify the
edges of the rectangle to be displayed on the screen.
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 pminrow, pmincol, sminrow,
or smincol are treated as if they were zero.
The pechochar routine is functionally equivalent to a call to addch
followed by a call to refresh(3x), a call to waddch followed by a call
to wrefresh, or a call to waddch followed by a call to prefresh. 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 pechochar, the last location of the pad on
the screen is reused for the arguments to prefresh.
The pecho_wchar function is the analogous wide-character form of
pechochar. It outputs one character to a pad and immediately refreshes
the pad. It does this by a call to wadd_wch followed by a call to
prefresh.
Routines that return an integer return ERR upon failure and OK (SVr4
only specifies "an integer value other than ERR") upon successful
completion.
Routines that return pointers return NULL on error, and set errno to
ENOMEM.
X/Open does not define any error conditions. In this implementation
prefresh and pnoutrefresh
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.
pechochar
returns an error if the window is not really a pad, and the
associated call to wechochar returns an error.
pecho_wchar
returns an error if the window is not really a pad, and the
associated call to wecho_wchar returns an error.
Note that pechochar may be a macro.
BSD curses has no pad feature.
SVr2 curses (1986) provided the newpad and related functions,
documenting them in a single line each. SVr3 (1987) provided more
extensive documentation.
The documentation does not explain the term pad. However, the Apollo
Aegis workstation operating system supported a graphical pad feature:
o These graphical pads could be much larger than the computer's
display.
o The read-only output from a command could be scrolled back to
inspect, and select text from the pad.
The two uses may be related.
The XSI Curses standard, Issue 4 describes these functions, without
significant change from the SVr3 documentation. It describes no error
conditions. The behavior of subpad if the parent window is not a pad
is undocumented, and is not checked by the vendor Unix implementations:
o SVr4 curses sets a flag in the WINDOW structure in newpad which
tells if the window is a pad.
However, it uses this information only in waddch (to decide if it
should call wrefresh) and wscrl (to avoid scrolling a pad), and
does not check in wrefresh to ensure that the pad is refreshed
properly.
o Solaris X/Open Curses checks if a window is a pad in wnoutrefresh,
returning ERR in that case.
However, it only sets the flag for subwindows if the parent window
is a pad. Its newpad function does not set this information.
Consequently, the check will never fail.
It makes no comparable check in pnoutrefresh, though interestingly
enough, a comment in the source code states that the lack of a
check was an MKS extension.
o NetBSD 7 curses sets a flag in the WINDOW structure for newpad and
subpad, using this to help with the distinction between
wnoutrefresh and pnoutrefresh.
It does not check for the case where a subwindow is created in a
pad using subwin or derwin.
The dupwin function returns a regular window when duplicating a
pad. Likewise, getwin always returns a window, even if the saved
data was from a pad.
This implementation
o sets a flag in the WINDOW structure for newpad and subpad,
o allows a subwin or derwin call to succeed having a pad parent by
forcing the subwindow to be a pad,
o checks in both wnoutrefresh and pnoutrefresh to ensure that pads
and windows are handled distinctly, and
o ensures that dupwin and getwin treat pads versus windows
consistently.
curses(3x), curs_addch(3x), curs_refresh(3x), curs_touch(3x)
ncurses 6.4 2023-11-11 curs_pad(3x)