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default_colors 3x

default_colors(3x)                                          default_colors(3x)




NAME

       use_default_colors, assume_default_colors - use terminal's default col-
       ors


SYNOPSIS

       #include <curses.h>

       int use_default_colors(void);
       int assume_default_colors(int fg, int bg);


DESCRIPTION

       The use_default_colors and assume_default_colors functions  are  exten-
       sions to the curses library.  They are used with terminals that support
       ISO 6429 color, or equivalent.  These terminals allow  the  application
       to  reset  color  to an unspecified default value (e.g., with SGR 39 or
       SGR 49).

       Applications that paint a colored background over the whole  screen  do
       not  take  advantage  of  SGR  39  and  SGR  49.  Some applications are
       designed to work with the default background,  using  colors  only  for
       text.  For example, there are several implementations of the ls program
       which use colors to denote different file types or permissions.   These
       "color  ls"  programs  do  not necessarily modify the background color,
       typically using only the setaf terminfo capability  to  set  the  fore-
       ground  color.   Full-screen  applications  that use default colors can
       achieve similar visual effects.

       The first function, use_default_colors  tells  the  curses  library  to
       assign  terminal  default  foreground/background colors to color number
       -1. So init_pair(x,COLOR_RED,-1) will  initialize  pair  x  as  red  on
       default  background and init_pair(x,-1,COLOR_BLUE) will initialize pair
       x as default foreground on blue.

       The other, assume_default_colors is a refinement which tells which col-
       ors  to  paint  for  color  pair 0.  This function recognizes a special
       color number -1, which denotes the default terminal color.

       The following are equivalent:
              use_default_colors();
              assume_default_colors(-1,-1);

       These are ncurses extensions.  For other curses implementations,  color
       number -1 does not mean anything, just as for ncurses before a success-
       ful call of use_default_colors or assume_default_colors.

       Other curses implementations do not  allow  an  application  to  modify
       color  pair  0.  They assume that the background is COLOR_BLACK, but do
       not ensure that the color pair 0 is painted to  match  the  assumption.
       If   your   application  does  not  use  either  use_default_colors  or
       assume_default_colors ncurses will paint a white foreground (text) with
       black background for color pair 0.


RETURN VALUE

       These  functions return the integer ERR upon failure and OK on success.
       They will fail if either the terminal does not support the orig_pair or
       orig_colors  capability.   If  the  initialize_pair  capability  is not
       found, this causes an error as well.


NOTES

       Associated with this extension, the init_pair function accepts negative
       arguments to specify default foreground or background colors.

       The  use_default_colors  function  was added to support ded.  This is a
       full-screen application which uses curses to manage only  part  of  the
       screen.  The bottom portion of the screen, which is of adjustable size,
       is left uncolored to display the results from shell commands.  The  top
       portion  of  the screen colors filenames using a scheme like the "color
       ls" programs.  Attempting to manage the background color of the  screen
       for this application would give unsatisfactory results for a variety of
       reasons.  This extension was devised after noting that color xterm (and
       similar  programs) provides a background color which does not necessar-
       ily correspond to any of the ANSI colors.   While  a  special  terminfo
       entry  could  be  constructed using nine colors, there was no mechanism
       provided within  curses  to  account  for  the  related  orig_pair  and
       back_color_erase capabilities.

       The assume_default_colors function was added to solve a different prob-
       lem: support for applications which would use environment variables and
       other  configuration to bypass curses' notion of the terminal's default
       colors, setting specific values.


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

       curs_color(3x), ded(1).


AUTHOR

       Thomas Dickey (from an analysis of the requirements for color xterm for
       XFree86 3.1.2C, February 1996).



                                                            default_colors(3x)