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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
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