curs_color
Section: Miscellaneous Library Functions (3X)
Updated:
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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 supports 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.
Color Rendering
The
curses library combines these inputs to produce the
actual foreground and background colors shown on the screen:
- *
-
per-character video attributes (e.g., via waddch),
- *
-
the window attribute (e.g., by wattrset), and
- *
-
the background character (e.g., wbkgdset).
Per-character and window attributes are usually set by a parameter containing
video attributes including a COLOR_PAIR value.
Some functions such as wattr_set use a separate parameter which
is the color pair number.
The background character is a special case: it includes a character value,
just as if it were passed to waddch.
The curses library does the actual work of combining these color
pairs in an internal function called from waddch:
- *
-
If the parameter passed to waddch is blank,
and it uses the special color pair 0,
-
- *
-
curses next checks the window attribute.
- *
-
If the window attribute does not use color pair 0,
curses uses the color pair from the window attribute.
- *
-
Otherwise, curses uses the background character.
- *
-
If the parameter passed to waddch is not blank,
or it does not use the special color pair 0,
curses prefers the color pair from the parameter,
if it is nonzero.
Otherwise, it tries the window attribute next, and finally the
background character.
Some curses functions such as wprintw call waddch.
Those do not combine its parameter with a color pair.
Consequently those calls use only the window attribute or
the background character.
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 does this:
- *
-
It initializes two global variables, COLORS and
COLOR_PAIRS (respectively defining the maximum number of colors
and color-pairs the terminal can support).
- *
-
It initializes the special color pair 0 to the default foreground
and background colors.
No other color pairs are initialized.
- *
-
It restores the colors on the terminal to the values
they had when the terminal was just turned on.
- *
-
If the terminal supports the initc (initialize_color) capability,
start_color
initializes its internal table representing the
red, green and blue components of the color palette.
-
The components depend on whether the terminal uses
CGA (aka "ANSI") or
HLS (i.e., the hls (hue_lightness_saturation) capability is set).
The table is initialized first for eight basic colors
(black, red, green, yellow, blue, magenta, cyan, and white),
and after that (if the terminal supports more than eight colors)
the components are initialized to 1000.
-
start_color does not attempt to set the terminal's color palette
to match its built-in table.
An application may use init_color to alter the internal table
along with the terminal's color.
These limits apply to color values and color pairs.
Values outside these limits are not legal, and may result in a runtime error:
- *
-
COLORS corresponds to the terminal database's max_colors capability,
which is typically a signed 16-bit integer (see terminfo(5)).
- *
-
color values are expected to be in the range 0 to COLORS-1,
inclusive (including 0 and COLORS-1).
- *
-
a special color value -1 is used in certain extended functions
to denote the default color (see use_default_colors).
- *
-
COLOR_PAIRS corresponds to the terminal database's max_pairs capability,
which is typically a signed 16-bit integer (see terminfo(5)).
- *
-
legal color pair values are in the range 1 to COLOR_PAIRS-1,
inclusive.
- *
-
color pair 0 is special; it denotes ``no color''.
-
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.
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 first argument must be a legal color pair value.
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 second and third arguments must be legal color values.
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 first argument must be a legal color value;
default colors are not allowed here.
(See the section Colors for the default color index.)
Each of the last three arguments
must be a value in the range 0 through 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 first argument must be a legal color value, i.e.,
0 through COLORS-1, inclusive.
The values that are stored at the addresses pointed to by the
last three arguments are in the range
0 (no component) through 1000 (maximum amount of component), inclusive.
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 first argument must be a legal color value,
i.e., in the range 1 through COLOR_PAIRS-1, inclusive.
The values that are stored at the addresses pointed
to by the second and third arguments are in the
range 0 through COLORS, inclusive.
Colors
In
<curses.h> the following macros are defined.
These are the standard colors (ISO-6429).
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 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 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
curses(3X),
curs_initscr(3X),
curs_attr(3X),
curs_variables(3X),
default_colors(3X)
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- Overview
-
- Color Rendering
-
- Routine Descriptions
-
- Colors
-
- RETURN VALUE
-
- NOTES
-
- PORTABILITY
-
- SEE ALSO
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