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 capability. 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 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.
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, except that 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 background.
- 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 facilitates 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 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 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 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 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 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
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 capability is absent
from the terminal 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 associated 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 bkgd(3NCURSES).
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 maximums for COLORS
and COLOR_PAIRS.
The init_pair routine accepts negative values of foreground and
background color to support the use_default_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 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.
SEE ALSO
ncurses(3NCURSES), initscr(3NCURSES), attr(3NCURSES),
default_colors(3NCURSES)
color(3NCURSES)