default_colors(3X)               Library calls              default_colors(3X)

NAME

     use_default_colors, assume_default_colors - use terminal's default colors
     in curses

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 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 foreground 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:
            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 successful
     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 necessarily
     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.

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.

AUTHORS

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

SEE ALSO

     ded(1), curs_color(3X)

ncurses 6.6                       2024-04-13                default_colors(3X)