default_colors(3NCURSES) default_colors(3NCURSES)
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 de-
signed 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 as-
sign 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 de-
fault 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 as-
sume_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 en-
try could be constructed using nine colors, there was no mechanism pro-
vided 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
ded(1), color(3NCURSES).
AUTHOR
Thomas Dickey (from an analysis of the requirements for color xterm for
XFree86 3.1.2C, February 1996).
default_colors(3NCURSES)
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