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NAME | SYNOPSIS | DESCRIPTION | CONSTANTS | VARIABLES | FUNCTIONS | RETURN VALUE | NOTES | HISTORY | PORTABILITY | SEE ALSO | COLOPHON |
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curs_color(3X) curs_color(3X)
start_color, has_colors, can_change_color, init_pair, init_color,
init_extended_pair, init_extended_color, color_content,
pair_content, extended_color_content, extended_pair_content,
reset_color_pairs, COLOR_PAIR, PAIR_NUMBER - curses color
manipulation routines
#include <curses.h>
int start_color(void);
bool has_colors(void);
bool can_change_color(void);
int init_pair(short pair, short f, short b);
int init_color(short color, short r, short g, short b);
/* extensions */
int init_extended_pair(int pair, int f, int b);
int init_extended_color(int color, int r, int g, int b);
int color_content(short color, short *r, short *g, short *b);
int pair_content(short pair, short *f, short *b);
/* extensions */
int extended_color_content(int color, int *r, int *g, int *b);
int extended_pair_content(int pair, int *f, int *b);
/* extensions */
void reset_color_pairs(void);
int COLOR_PAIR(int n);
PAIR_NUMBER(attrs);
Overview
curses supports color attributes on terminals with that capabili‐
ty. 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 characters are displayed). A programmer initializes a
color-pair with the routine init_pair. After it has been ini‐
tialized, COLOR_PAIR(n) can be used to convert the pair to a
video attribute.
If a terminal is capable of redefining colors, the programmer can
use the routine init_color to change the definition 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
color_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.
Color Rendering
The curses library combines these inputs to produce the actual
foreground and background colors shown on the screen:
• per-character video attributes (e.g., via waddch),
• the window attribute (e.g., by wattrset), and
• the background character (e.g., wbkgdset).
Per-character and window attributes are usually set by a parame‐
ter containing video attributes including a color pair value.
Some functions such as wattr_set use a separate parameter which
is the color pair number.
The background character is a special case: it includes a charac‐
ter value, just as if it were passed to waddch.
The curses library does the actual work of combining these color
pairs in an internal function called from waddch:
• If the parameter passed to waddch is blank, and it uses the
special color pair 0,
• curses next checks the window attribute.
• If the window attribute does not use color pair 0, curses
uses the color pair from the window attribute.
• Otherwise, curses uses the background character.
• If the parameter passed to waddch is not blank, or it does
not use the special color pair 0, curses prefers the color
pair from the parameter, if it is nonzero. Otherwise, it
tries the window attribute next, and finally the background
character.
Some curses functions such as wprintw call waddch. Those do not
combine its parameter with a color pair. Consequently those
calls use only the window attribute or the background character.
In <curses.h> the following macros are defined. These are the
standard colors (ISO-6429). 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
Some terminals support more than the eight (8) “ANSI” colors.
There are no standard names for those additional colors.
COLORS
is initialized by start_color to the maximum number of colors the
terminal can support.
COLOR_PAIRS
is initialized by start_color to the maximum number of color
pairs the terminal can support.
start_color
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:
• It initializes two global variables, COLORS and COLOR_PAIRS
(respectively defining the maximum number of colors and col‐
or-pairs the terminal can support).
• It initializes the special color pair 0 to the default fore‐
ground and background colors. No other color pairs are ini‐
tialized.
• It restores the colors on the terminal to the values they had
when the terminal was just turned on.
• If the terminal supports the initc (initialize_color) capa‐
bility, start_color initializes its internal table represent‐
ing 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_saturation) ca‐
pability is set). The table is initialized first for eight
basic colors (black, red, green, yellow, blue, magenta, cyan,
and white), using weights that depend upon the CGA/HLS
choice. For “ANSI” colors the weights are 680 or 0 depending
on whether the corresponding red, green, or blue component is
used or not. That permits using 1000 to represent
bold/bright colors. After the initial eight colors (if the
terminal supports more than eight colors) the components are
initialized using the same pattern, but with weights of 1000.
SVr4 uses a similar scheme, but uses 1000 for the components
of the initial eight colors.
start_color does not attempt to set the terminal's color
palette to match its built-in table. An application may use
init_color to alter the internal table along with the termi‐
nal's color.
These limits apply to color values and color pairs. Values out‐
side these limits are not legal, and may result in a runtime er‐
ror:
• COLORS corresponds to the terminal database's max_colors ca‐
pability, (see terminfo(5)).
• color values are expected to be in the range 0 to COLORS-1,
inclusive (including 0 and COLORS-1).
• a special color value -1 is used in certain extended func‐
tions to denote the default color (see use_default_col‐
ors(3X)).
• COLOR_PAIRS corresponds to the terminal database's max_pairs
capability, (see terminfo(5)).
• legal color pair values are in the range 1 to COLOR_PAIRS-1,
inclusive.
• 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 application.
has_colors
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 attribute.
can_change_color
The can_change_color routine requires no arguments. It returns
TRUE if the terminal supports colors and can change their defini‐
tions; other, it returns FALSE. This routine facilitates writing
terminal-independent programs.
init_pair
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 first argument must be a legal color pair value. If de‐
fault colors are used (see use_default_colors(3X)) the upper
limit is adjusted to allow for extra pairs which use a de‐
fault color in foreground and/or background.
• The second and third arguments must be legal color values.
If the color-pair was previously initialized, the screen is re‐
freshed 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(3X) routine, or to specify the use of de‐
fault colors (color number -1) if you first invoke the use_de‐
fault_colors(3X) routine.
init_extended_pair
Because init_pair uses signed shorts for its parameters, that
limits color-pairs and color-values to 32767 on modern hardware.
The extension init_extended_pair uses ints for the color-pair and
color-value, allowing a larger number of colors to be supported.
init_color
The init_color routine changes the definition of a color. It
takes four arguments: the number of the color to be changed fol‐
lowed by three RGB values (for the amounts of red, green, and
blue components).
• The first argument must be a legal color value; default col‐
ors are not allowed here. (See the section Colors for the
default color index.)
• 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.
init_extended_color
Because init_color uses signed shorts for its parameters, that
limits color-values and their red, green, and blue components to
32767 on modern hardware. The extension init_extended_color uses
ints for the color value and for setting the red, green, and blue
components, allowing a larger number of colors to be supported.
color_content
The color_content routine gives programmers a way to find the in‐
tensity 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.
extended_color_content
Because color_content uses signed shorts for its parameters, that
limits color-values and their red, green, and blue components to
32767 on modern hardware. The extension extended_color_content
uses ints for the color value and for returning the red, green,
and blue components, allowing a larger number of colors to be
supported.
pair_content
The pair_content routine allows programmers to find out what col‐
ors 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, inclusive.
• The values that are stored at the addresses pointed to by the
second and third arguments are in the range 0 through COLORS,
inclusive.
extended_pair_content
Because pair_content uses signed shorts for its parameters, that
limits color-pair and color-values to 32767 on modern hardware.
The extension extended_pair_content uses ints for the color pair
and for returning the foreground and background colors, allowing
a larger number of colors to be supported.
reset_color_pairs
The extension reset_color_pairs tells ncurses to discard all of
the color-pair information which was set with init_pair. It also
touches the current- and standard-screens, allowing an applica‐
tion to switch color palettes rapidly.
PAIR_NUMBER
PAIR_NUMBER(attrs) extracts the color value from its attrs para‐
meter and returns it as a color pair number.
COLOR_PAIR
Its inverse COLOR_PAIR(n) converts a color pair number to an at‐
tribute. Attributes can hold color pairs in the range 0 to 255.
If you need a color pair larger than that, you must use functions
such as attr_set (which pass the color pair as a separate parame‐
ter) rather than the legacy functions such as attrset.
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 suc‐
cessful completion.
X/Open defines no error conditions. SVr4 does document some er‐
ror conditions which apply in general:
• This implementation will return ERR on attempts to use color
values outside the range 0 to COLORS-1 (except for the de‐
fault colors extension), or use color pairs outside the range
0 to COLOR_PAIRS-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 returned from secondary functions such as
init_pair if start_color was not called.
• SVr4 does much the same, except that it returns ERR from
pair_content if the pair was not initialized using init_pairs
and it returns ERR from color_content if the terminal does
not support changing colors.
This implementation does not return ERR for either case.
Specific functions make additional checks:
init_color
returns an error if the terminal does not support this
feature, e.g., if the initialize_color capability is ab‐
sent from the terminal description.
start_color
returns an error if the color table cannot be allocated.
In the ncurses implementation, there is a separate color activa‐
tion flag, color palette, color pairs table, and associated COL‐
ORS and COLOR_PAIRS counts for each screen; the start_color func‐
tion only affects the current screen. The SVr4/XSI interface is
not really designed with this in mind, and historical implementa‐
tions may use a single shared color palette.
Setting an implicit background color via a color pair affects on‐
ly 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 older x86 machines (e.g., i386, i486)
with VGA-compatible graphics:
• COLOR_YELLOW is actually brown. To get yellow, use COL‐
OR_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 compati‐
bles) do the wrong thing when you try to set a bright “yel‐
low” background (you get a blinking yellow foreground in‐
stead).
• Color RGB values are not settable.
SVr3.2 introduced color support to curses in 1987.
SVr4 made internal changes, e.g., moving the storage for the col‐
or state from SP (the SCREEN structure) to cur_term (the TERMINAL
structure), but provided the same set of library functions.
SVr4 curses limits the number of color pairs to 64, reserving
color pair zero (0) as the terminal's initial uncolored state.
This limit arises because the color pair information is a bit‐
field in the chtype data type (denoted by A_COLOR).
Other implementations of curses had different limits:
• PCCurses (1987-1990) provided for only eight (8) colors.
• PDCurses (1992-present) inherited the 8-color limitation from
PCCurses, but changed this to 256 in version 2.5 (2001),
along with changing chtype from 16-bits to 32-bits.
• X/Open Curses (1992-present) added a new structure cchar_t to
store the character, attributes and color-pair values, allow‐
ing increased range of color-pairs. Both color-pairs and
color-values used a signed short, limiting values to 15 bits.
• ncurses (1992-present) uses eight bits for A_COLOR in chtype
values.
Version 5.3 provided a wide-character interface (2002), but
left color-pairs as part of the attributes-field.
Since version 6 (2015), ncurses uses a separate int for col‐
or-pairs in the cchar_t values. When those color-pair values
fit in 8 bits, ncurses allows color-pairs to be manipulated
via the functions using chtype values.
• NetBSD curses used 6 bits from 2000 (when colors were first
supported) until 2004. At that point, NetBSD changed to use
10 bits. As of 2021, that size is unchanged. Like ncurses
before version 6, the NetBSD color-pair information is stored
in the attributes field of cchar_t, limiting the number of
color-pairs by the size of the bitfield.
This implementation satisfies XSI Curses's minimum maximums for
COLORS and COLOR_PAIRS.
The init_pair routine accepts negative values of foreground and
background color to support the use_default_colors(3X) 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 assume_default_col‐
ors(3X) extension.
This implementation checks the pointers, e.g., for the values re‐
turned by color_content and pair_content, and will treat those as
optional parameters when null.
X/Open Curses does not specify a limit for the number of colors
and color pairs which a terminal can support. However, in its
use of short for the parameters, it carries over SVr4's implemen‐
tation detail for the compiled terminfo database, which uses
signed 16-bit numbers. This implementation provides extended
versions of those functions which use short parameters, allowing
applications to use larger color- and pair-numbers.
The reset_color_pairs function is an extension of ncurses.
curses(3X), curs_initscr(3X), curs_attr(3X), curs_variables(3X),
default_colors(3X)
This page is part of the ncurses (new curses) project. Informa‐
tion about the project can be found at
⟨https://www.gnu.org/software/ncurses/ncurses.html⟩. If you have
a bug report for this manual page, send it to
[email protected]. This page was obtained from the
project's upstream Git mirror of the CVS repository
⟨https://github.com/mirror/ncurses.git⟩ on 2024-06-14. (At that
time, the date of the most recent commit that was found in the
repository was 2023-03-12.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
curs_color(3X)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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