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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | PORTABILITY | SEE ALSO | AUTHOR | COLOPHON |
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new_pair(3X) new_pair(3X)
alloc_pair, find_pair, free_pair - new curses color-pair
functions
#include <curses.h>
int alloc_pair(int fg, int bg);
int find_pair(int fg, int bg);
int free_pair(int pair);
These functions are an extension to the curses library. They
permit an application to dynamically allocate a color pair using
the foreground/background colors rather than assign a fixed color
pair number, and return an unused pair to the pool.
The number of colors may be related to the number of possible
color pairs for a given terminal, or it may not:
• While almost all terminals allow setting the color attributes
independently, it is unlikely that your terminal allows you
to modify the attributes of a given character cell without
rewriting it. That is, the foreground and background colors
are applied as a pair.
• Color pairs are the curses library's way of managing a color
palette on a terminal. If the library does not keep track of
the combinations of colors which are displayed, it will be
inefficient.
• For simple terminal emulators with only a few dozen color
combinations, it is convenient to use the maximum number of
combinations as the limit on color pairs:
COLORS * COLORS
• Terminals which support default colors distinct from “ANSI
colors” add to the possible combinations, producing this
total:
( COLORS + 1 ) * ( COLORS + 1 )
• An application might use up to a few dozen color pairs to
implement a predefined color scheme.
Beyond that lies in the realm of programs using the
foreground and background colors for “ASCII art” (or some
other non-textual application).
Also beyond those few dozen pairs, the required size for a
table to represent the combinations grows rapidly with an
increasing number of colors.
These functions allow a developer to let the screen library
manage color pairs.
alloc_pair
The alloc_pair function accepts parameters for foreground and
background color, and checks if that color combination is already
associated with a color pair.
• If the combination already exists, alloc_pair returns the
existing pair.
• If the combination does not exist, alloc_pair allocates a new
color pair and returns that.
• If the table fills up, alloc_pair discards the least-recently
allocated entry using free_pair and allocates a new color
pair.
All of the color pairs are allocated from a table of possible
color pairs. The size of the table is determined by the terminfo
pairs capability. The table is shared with init_pair; in fact
alloc_pair calls init_pair after updating the ncurses library's
fast index to the colors versus color pairs.
find_pair
The find_pair function accepts parameters for foreground and
background color, and checks if that color combination is already
associated with a color pair, returning the pair number if it has
been allocated. Otherwise it returns -1.
free_pair
Marks the given color pair as unused, i.e., like color pair 0.
The alloc_pair function returns a color pair number in the range
1 through COLOR_PAIRS-1, unless it encounters an error updating
its fast index to the color pair values, preventing it from
allocating a color pair. In that case, it returns -1.
The find_pair function returns a color pair number if the given
color combination has been associated with a color pair, or -1 if
not.
Likewise, free_pair returns OK unless it encounters an error
updating the fast index or if no such color pair is in use.
These routines are specific to ncurses. They were not supported
on Version 7, BSD or System V implementations. It is recommended
that any code depending on them be conditioned using
NCURSES_VERSION.
curs_color(3X).
Thomas Dickey.
This page is part of the ncurses (new curses) project.
Information about the project can be found at
⟨https://www.gnu.org/software/ncurses/ncurses.html⟩. If you have
a bug report for this manual page, send it to
bug-ncurses-request@gnu.org. This page was obtained from the
project's upstream Git mirror of the CVS repository
⟨https://github.com/mirror/ncurses.git⟩ on 2024-06-14. (At that
time, the date of the most recent commit that was found in the
repository was 2023-03-12.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
new_pair(3X)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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