alloc_pair, find_pair, free_pair - dynamically allocate curses color pairs

       Thomas Dickey

       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 defaultcolors 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 whether 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 whether 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.

alloc_pair, find_pair, free_pair - dynamically allocate curses color pairs

       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.

       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.

color(3NCURSES)

ncurses 6.5                                        2025-01-18                                 new_pair(3NCURSES)

#include<curses.h>intalloc_pair(intfg,intbg);intfind_pair(intfg,intbg);intfree_pair(intpair);