default_colors(3) UNIX Programmer's Manual default_colors(3)NAME
use_default_colors, assume_default_colors - use terminal's
default colors
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() func-
tions 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 back-
ground, 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 implementa-
tions, 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
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default_colors(3) UNIX Programmer's Manual default_colors(3)
painted to match the assumption. If your application does
not use either use_default_colors() or
assume_default_colors() ncurses will paint a white fore-
ground (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 found, this causes an error as
well.
NOTES
Associated with this extension, the init_pair(3) 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) pro-
vides a background color which does not necessarily
correspond to any of the ANSI colors. While a special ter-
minfo 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 sup-
ported on Version 7, BSD or System V implementations. It is
recommended that any code depending on them be conditioned
using NCURSES_VERSION.
SEE ALSOcurs_color(3), ded(1).
AUTHOR
Thomas Dickey (from an analysis of the requirements for
color xterm for XFree86 3.1.2C, February 1996).
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