assume_default_colors man page on Archlinux

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default_colors(3X)					    default_colors(3X)

       use_default_colors, assume_default_colors - use terminal's default col‐

       #include <curses.h>

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

       The  use_default_colors()  and  assume_default_colors()	functions  are
       extensions  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
       colors  to  paint for color pair 0.  This function recognizes a special
       color number -1, which denotes the default terminal color.

       The following are equivalent:

       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.

       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.

       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
       problem: support for applications which would use environment variables
       and  other  configuration  to  bypass  curses' notion of the terminal's
       default colors, setting specific values.

       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.

       curs_color(3X), ded(1).

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


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