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 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 ca-
pabilities and whether the programmer can change the col-
ors. The routine color_content allows a programmer to ex-
tract the amounts of red, green, and blue components in an
initialized color. The routine pair_content allows a pro-
grammer 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 applica-
tions:
- 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_col-
ors routine, or to specify the use of default colors (col-
or 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 re-
turns 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 argu-
ments. It returns TRUE if the terminal supports colors
and can change their definitions; other, it returns FALSE.
This routine facilitates writing terminal-independent pro-
grams. 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 ar-
gument 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 addresses of shorts for storing the fore-
ground 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 arguments 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 back-
ground 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 ma-
chines 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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