newpad, subpad, prefresh, pnoutrefresh,
pechochar, pecho_wchar - create and display curses pads
#include <ncurses/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.
- The pminrow and pmincol parameters specify the upper
left-hand corner of the rectangle to be displayed in the pad.
- 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:
- These graphical pads could be much larger than the computer's
display.
- 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:
- •
- 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.
- •
- 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.
- •
- 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
- sets a flag in the WINDOW structure for newpad and
subpad,
- allows a subwin or derwin call to succeed having a pad
parent by forcing the subwindow to be a pad,
- checks in both wnoutrefresh and pnoutrefresh to ensure that
pads and windows are handled distinctly, and
- ensures that dupwin and getwin treat pads versus windows
consistently.