NAME

       alloc_pair, find_pair, free_pair - new curses color-pair functions

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:

       •   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.

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.

SEE ALSO

       init_pair(3X).

AUTHOR

       Thomas Dickey.

                                                                                              new_pair(3NCURSES)