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() 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.
SEE ALSO¶
color(3NCURSES),
ded(1).
AUTHOR¶
Thomas Dickey (from an analysis of the requirements for color xterm for XFree86
3.1.2C, February 1996).