new_pair(3) Library calls new_pair(3)
NAME
alloc_pair, find_pair, free_pair - dynamically allocate curses color
pairs
SYNOPSIS
#include <curses.h>
int alloc_pair(int fg, int bg);
int find_pair(int fg, int bg);
int free_pair(int pair);
DESCRIPTION
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:
o 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.
o 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.
o 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
o Terminals which support default colors distinct from "ANSI colors"
add to the possible combinations, producing this total:
( COLORS + 1 ) * ( COLORS + 1 )
o 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.
o If the combination already exists, alloc_pair returns the existing
pair.
o If the combination does not exist, alloc_pair allocates a new color
pair and returns that.
o 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.
RETURN VALUE
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.
PORTABILITY
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.
AUTHORS
Thomas Dickey
SEE ALSO
curs_color(3X)
ncurses 6.5 2024-03-16 new_pair(3)
ncurses 6.5 - Generated Sat May 4 07:00:56 CDT 2024