curs_color(3) UNIX Programmer's Manual curs_color(3)
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);
Overview
curses support color attributes on terminals with that capa-
bility. 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 initialized, COLOR_PAIR(n), a
macro defined in <curses.h>, can be used as a new video at-
tribute. If a terminal is capable of redefining colors, the
programmer can use the routine init_color to change the de-
finition 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 program-
mer 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.
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 glo-
bal 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
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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 invoke 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 facili-
tates writing terminal-independent programs. For example, a
programmer can use it to decide whether to use color or some
other video attribute. 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 pro-
grammers a way to find the intensity of the red, green, and
blue (RGB) components in a color. It requires four argu-
ments: 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 argu-
ments are between 0 (no component) and 1000 (maximum amount
of component). 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 ad-
dresses of shorts for storing the foreground and the back-
ground 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.
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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
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 extension), or
use color pairs outside the range 0 to COLOR_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 returned from secondary func-
tions 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 ac-
tivation flag, color palette, color pairs table, and associ-
ated 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 back-
ground color used when parts of a window are blanked by
erasing or scrolling operations, see curs_bkgd(3). Several
caveats apply on 386 and 486 machines with VGA-compatible
graphics:
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- 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 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).
- Color RGB values are not settable.
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 ex-
tension, 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_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(3), curs_initscr(3), curs_attr(3), default_colors(3)
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