curs_color(3x) curs_color(3x)
start_color, init_pair, init_color, has_colors,
can_change_color, color_content, pair_content, COLOR_PAIR
- curses color manipulation routines
# 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);
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.
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 does this:
o It initializes two global variables, COLORS and COL-
OR_PAIRS (respectively defining the maximum number of
colors and color-pairs the terminal can support).
o It initializes the special color pair 0 to the default
foreground and background colors. No other color
pairs are initialized.
o It restores the colors on the terminal to the values
they had when the terminal was just turned on.
o If the terminal supports the initc (initialize_color)
capability, start_color initializes its internal table
representing the red, green and blue components of the
color palette.
The components depend on whether the terminal uses CGA
(aka "ANSI") or HLS (i.e., the hls (hue_lightness_sat-
uration) capability is set). The table is initialized
first for eight basic colors (black, red, green, yel-
low, blue, magenta, cyan, and white), and after that
(if the terminal supports more than eight colors) the
components are initialized to 1000.
start_color does not attempt to set the terminal's
color palette to match its built-in table. An appli-
cation may use init_color to alter the internal table
along with the terminal's color.
These limits apply to color values and color pairs. Val-
ues outside these limits are not legal, and may result in
a runtime error:
o COLORS corresponds to the terminal database's max_col-
ors capability, which is typically a signed 16-bit in-
teger (see terminfo(5)).
o color values are expected to be in the range 0 to COL-
ORS-1, inclusive (including 0 and COLORS-1).
o a special color value -1 is used in certain extended
functions to denote the default color (see use_de-
fault_colors).
o COLOR_PAIRS corresponds to the terminal database's
max_pairs capability, which is typically a signed
16-bit integer (see terminfo(5)).
o legal color pair values are in the range 1 to COL-
OR_PAIRS-1, inclusive.
o color pair 0 is special; it denotes "no color".
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 applica-
tion.
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:
o The first argument must be a legal color pair value.
If default colors are used (see use_default_colors)
the upper limit is adjusted to allow for extra pairs
which use a default color in foreground and/or back-
ground.
o The second and third arguments must be legal color
values.
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 first argument must
be a legal color value; default colors are not allowed
here. (See the section Colors for the default color in-
dex.) Each of the last three arguments must be a value in
the range 0 through 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 first argument must be a legal color
value, i.e., 0 through COLORS-1, inclusive. The values
that are stored at the addresses pointed to by the last
three arguments are in the range 0 (no component) through
1000 (maximum amount of component), inclusive.
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 first argument must be a legal color
value, i.e., in the range 1 through COLOR_PAIRS-1, inclu-
sive. The values that are stored at the addresses pointed
to by the second and third arguments are in the range 0
through COLORS, inclusive.
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
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_PAIRS-1. Color values used in init_color must be in
the range 0 to 1000. An error is returned from all func-
tions if the terminal has not been initialized. An error
is returned from secondary functions such as init_pair if
start_color was not called.
init_color
returns an error if the terminal does not support
this feature, e.g., if the initialize_color capa-
bility is absent from the terminal description.
start_color
returns an error if the color table cannot be al-
located.
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:
o COLOR_YELLOW is actually brown. To get yellow, use
COLOR_YELLOW combined with the A_BOLD attribute.
o The A_BLINK attribute should in theory cause the back-
ground 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).
o Color RGB values are not settable.
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.
curses(3x), curs_initscr(3x), curs_attr(3x), curs_vari-
ables(3x), default_colors(3x)
curs_color(3x)