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_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.
- 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),
curses_variables(3NCURSES),
default_colors(3NCURSES)