manpagez: man pages & more
man new_pair(3)
Home | html | info | man
new_pair(3)                                                      new_pair(3)




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  fore-
       ground/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 inde-
           pendently, 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  combina-
           tions,  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 appli-
           cation).

           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 back-
       ground color, and checks if that color combination is  already  associ-
       ated 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 allo-
           cated 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 capa-
       bility.  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.  Oth-
       erwise 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(3)

ncurses 6.0 - Generated Mon May 8 15:58:31 CDT 2017
© manpagez.com 2000-2018
Individual documents may contain additional copyright information.