curs_color 3x
curs_color(3x) curs_color(3x)
NAME
start_color, init_pair, init_color, has_colors,
can_change_color, color_content, pair_content, COLOR_PAIR
- curses color manipulation routines
SYNOPSIS
# include <curses.h>
int start_color(void);
int init_pair(short pair, short f, short b);
int init_color(short color, short r, short g, short b);
bool has_colors(void);
bool can_change_color(void);
int color_content(short color, short *r, short *g, short
*b);
int pair_content(short pair, short *f, short *b);
DESCRIPTION
Overview
curses support color attributes on terminals with that ca-
pability. To use these routines start_color must be
called, usually right after initscr. Colors are always
used in pairs (referred to as color-pairs). A color-pair
consists of a foreground color (for characters) and a
background color (for the blank field on which the charac-
ters are displayed). A programmer initializes a color-
pair with the routine init_pair. After it has been ini-
tialized, COLOR_PAIR(n), a macro defined in <curses.h>,
can be used as a new video attribute.
If a terminal is capable of redefining colors, the pro-
grammer can use the routine init_color to change the defi-
nition of a color. The routines has_colors and
can_change_color return TRUE or FALSE, depending on
whether the terminal has color capabilities and whether
the programmer can change the colors. The routine col-
or_content allows a programmer to extract the amounts of
red, green, and blue components in an initialized color.
The routine pair_content allows a programmer to find out
how a given color-pair is currently defined.
Routine Descriptions
The start_color routine requires no arguments. It must be
called if the programmer wants to use colors, and before
any other color manipulation routine is called. It is
good practice to call this routine right after initscr.
start_color initializes eight basic colors (black, red,
green, yellow, blue, magenta, cyan, and white), and two
global variables, COLORS and COLOR_PAIRS (respectively
defining the maximum number of colors and color-pairs the
terminal can support). It also restores the colors on the
terminal to the values they had when the terminal was just
turned on.
The init_pair routine changes the definition of a color-
pair. It takes three arguments: the number of the color-
pair to be changed, the foreground color number, and the
background color number. For portable applications:
- The value of the first argument must be between 1 and
COLOR_PAIRS-1.
- The value of the second and third arguments must be
between 0 and COLORS. Color pair 0 is assumed to be
white on black, but is actually whatever the terminal
implements before color is initialized. It cannot be
modified by the application.
If the color-pair was previously initialized, the screen
is refreshed and all occurrences of that color-pair are
changed to the new definition.
As an extension, ncurses allows you to set color pair 0
via the assume_default_colors routine, or to specify the
use of default colors (color number -1) if you first in-
voke the use_default_colors routine.
The init_color routine changes the definition of a color.
It takes four arguments: the number of the color to be
changed followed by three RGB values (for the amounts of
red, green, and blue components). The value of the first
argument must be between 0 and COLORS. (See the section
Colors for the default color index.) Each of the last
three arguments must be a value between 0 and 1000. When
init_color is used, all occurrences of that color on the
screen immediately change to the new definition.
The has_colors routine requires no arguments. It returns
TRUE if the terminal can manipulate colors; otherwise, it
returns FALSE. This routine facilitates writing terminal-
independent programs. For example, a programmer can use
it to decide whether to use color or some other video at-
tribute.
The can_change_color routine requires no arguments. It
returns TRUE if the terminal supports colors and can
change their definitions; other, it returns FALSE. This
routine facilitates writing terminal-independent programs.
The color_content routine gives programmers a way to find
the intensity of the red, green, and blue (RGB) components
in a color. It requires four arguments: the color number,
and three addresses of shorts for storing the information
about the amounts of red, green, and blue components in
the given color. The value of the first argument must be
between 0 and COLORS. The values that are stored at the
addresses pointed to by the last three arguments are be-
tween 0 (no component) and 1000 (maximum amount of compo-
nent).
The pair_content routine allows programmers to find out
what colors a given color-pair consists of. It requires
three arguments: the color-pair number, and two addresses
of shorts for storing the foreground and the background
color numbers. The value of the first argument must be
between 1 and COLOR_PAIRS-1. The values that are stored
at the addresses pointed to by the second and third argu-
ments are between 0 and COLORS.
Colors
In <curses.h> the following macros are defined. These are
the default colors. curses also assumes that COLOR_BLACK
is the default background color for all terminals.
COLOR_BLACK
COLOR_RED
COLOR_GREEN
COLOR_YELLOW
COLOR_BLUE
COLOR_MAGENTA
COLOR_CYAN
COLOR_WHITE
RETURN VALUE
The routines can_change_color() and has_colors() return
TRUE or FALSE.
All other routines return the integer ERR upon failure and
an OK (SVr4 specifies only "an integer value other than
ERR") upon successful completion.
X/Open defines no error conditions. This implementation
will return ERR on attempts to use color values outside
the range 0 to COLORS-1 (except for the default colors ex-
tension), or use color pairs outside the range 0 to COL-
OR_PAIR-1. Color values used in init_color must be in the
range 0 to 1000. An error is returned from all functions
if the terminal has not been initialized. An error is re-
turned from secondary functions such as init_pair if
start_color was not called.
init_color
returns an error if the terminal does not sup-
port this feature, e.g., if the initial-
ize_color capability is absent from the termi-
nal description.
start_color
returns an error If the color table cannot be
allocated.
NOTES
In the ncurses implementation, there is a separate color
activation flag, color palette, color pairs table, and as-
sociated COLORS and COLOR_PAIRS counts for each screen;
the start_color function only affects the current screen.
The SVr4/XSI interface is not really designed with this in
mind, and historical implementations may use a single
shared color palette.
Note that setting an implicit background color via a color
pair affects only character cells that a character write
operation explicitly touches. To change the background
color used when parts of a window are blanked by erasing
or scrolling operations, see curs_bkgd(3x).
Several caveats apply on 386 and 486 machines with VGA-
compatible graphics:
- COLOR_YELLOW is actually brown. To get yellow, use
COLOR_YELLOW combined with the A_BOLD attribute.
- The A_BLINK attribute should in theory cause the
background to go bright. This often fails to work,
and even some cards for which it mostly works (such
as the Paradise and compatibles) do the wrong thing
when you try to set a bright "yellow" background (you
get a blinking yellow foreground instead).
- Color RGB values are not settable.
PORTABILITY
This implementation satisfies XSI Curses's minimum maxi-
mums for COLORS and COLOR_PAIRS.
The init_pair routine accepts negative values of fore-
ground and background color to support the use_de-
fault_colors extension, but only if that routine has been
first invoked.
The assumption that COLOR_BLACK is the default background
color for all terminals can be modified using the as-
sume_default_colors extension.
This implementation checks the pointers, e.g., for the
values returned by color_content and pair_content, and
will treat those as optional parameters when null.
SEE ALSO
curses(3x), curs_initscr(3x), curs_attr(3x), default_col-
ors(3x)
curs_color(3x)
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