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 dis-
played). A programmer initializes a color-pair with the routine
init_pair. After it has been initialized, COLOR_PAIR(n), a macro de-
fined in <curses.h>, can be used as a new video attribute. If a termi-
nal is capable of redefining colors, the programmer can use the routine
init_color to change the definition of a color. The routines has_col-
ors 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 manipu-
lation 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 COL-
OR_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 ac-
tually whatever the terminal implements before color is initial-
ized. It cannot be modified by the application.
turns 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 facil-
itates writing terminal-independent programs. The color_content rou-
tine 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 col-
or. 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 com-
ponent). 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 com-
pletion.
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 fea-
ture, e.g., if the initialize_color capability is absent
parts of a window are blanked by erasing or scrolling operations, see
curs_bkgd(3X). 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 back-
ground 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 pa-
rameters when null.
SEE ALSO
curses(3X), curs_initscr(3X), curs_attr(3X), default_colors(3X)
curs_color(3X)
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