start_color,
has_colors,
can_change_color,
init_pair,
init_color,
init_extended_pair,
init_extended_color,
color_content,
pair_content,
extended_color_content,
extended_pair_content,
reset_color_pairs,
COLOR_PAIR,
PAIR_NUMBER -
curses color manipulation routines
#include <curses.h>
int start_color(void);
bool has_colors(void);
bool can_change_color(void);
int init_pair(short pair, short f, short
b );
int init_color(short color, short r, short
g, short b);
/* extensions */
int init_extended_pair(int pair, int f, int
b);
int init_extended_color(int color, int r, int
g, int b);
int color_content(short color, short *r, short
* g, short *b);
int pair_content(short pair, short *f, short
* b);
/* extensions */
int extended_color_content(int color, int *r, int
* g, int *b);
int extended_pair_content(int pair, int *f, int
* b);
/* extensions */
void reset_color_pairs(void);
int COLOR_PAIR(int n);
PAIR_NUMBER(attrs);
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) can be used to convert
the pair to a 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.
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.
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
Some terminals support more than the eight (8) “ANSI” colors.
There are no standard names for those additional colors.
is initialized by
start_color to the maximum number of colors the
terminal can support.
is initialized by
start_color to the maximum number of color pairs the
terminal can support.
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), using weights that depend upon the CGA/HLS
choice. For “ANSI” colors the weights are 680 or
0 depending on whether the corresponding red, green, or blue
component is used or not. That permits using 1000 to represent
bold/bright colors. After the initial eight colors (if the terminal
supports more than eight colors) the components are initialized using the
same pattern, but with weights of 1000. SVr4 uses a similar scheme,
but uses 1000 for the components of the initial eight colors.
-
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, (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(3X)).
- •
-
COLOR_PAIRS corresponds to the terminal database's
max_pairs capability, (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
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
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(3X)) 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(3X) routine, or to specify the use of default
colors (color number
-1) if you first invoke the
use_default_colors(3X) routine.
Because
init_pair uses signed
shorts for its parameters, that
limits color-pairs and color-values to 32767 on modern hardware. The extension
init_extended_pair uses
ints for the color-pair and color-value,
allowing a larger number of colors to be supported.
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.
Because
init_color uses signed
shorts for its parameters, that
limits color-values and their red, green, and blue components to 32767 on
modern hardware. The extension
init_extended_color uses
ints for
the color value and for setting the red, green, and blue components, allowing
a larger number of colors to be supported.
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.
Because
color_content uses signed
shorts for its parameters, that
limits color-values and their red, green, and blue components to 32767 on
modern hardware. The extension
extended_color_content uses
ints
for the color value and for returning the red, green, and blue components,
allowing a larger number of colors to be supported.
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.
Because
pair_content uses signed
shorts for its parameters, that
limits color-pair and color-values to 32767 on modern hardware. The extension
extended_pair_content uses
ints for the color pair and for
returning the foreground and background colors, allowing a larger number of
colors to be supported.
The extension
reset_color_pairs tells ncurses to discard all of the
color-pair information which was set with
init_pair. It also touches
the current- and standard-screens, allowing an application to switch color
palettes rapidly.
PAIR_NUMBER(attrs) extracts the color value from its
attrs
parameter and returns it as a color pair number.
Its inverse
COLOR_PAIR(n) converts a color pair number to
an attribute. Attributes can hold color pairs in the range 0 to 255. If you
need a color pair larger than that, you must use functions such as
attr_set (which pass the color pair as a separate parameter) rather
than the legacy functions such as
attrset.
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. SVr4 does document some error conditions
which apply in general:
- •
- 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.
- •
- SVr4 does much the same, except that it returns ERR
from pair_content if the pair was not initialized using
init_pairs and it returns ERR from color_content if
the terminal does not support changing colors.
- This implementation does not return ERR for either
case.
Specific functions make additional checks:
- 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.
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.
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 older x86 machines (e.g., i386, i486) 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.
SVr3.2 introduced color support to curses in 1987.
SVr4 made internal changes, e.g., moving the storage for the color state from
SP (the
SCREEN structure) to
cur_term (the
TERMINAL structure), but provided the same set of library functions.
SVr4 curses limits the number of color pairs to 64, reserving color pair zero
(0) as the terminal's initial uncolored state. This limit arises because the
color pair information is a bitfield in the
chtype data type (denoted
by
A_COLOR).
Other implementations of curses had different limits:
- •
- PCCurses (1987-1990) provided for only eight (8)
colors.
- •
- PDCurses (1992-present) inherited the 8-color limitation
from PCCurses, but changed this to 256 in version 2.5 (2001), along with
changing chtype from 16-bits to 32-bits.
- •
- X/Open Curses (1992-present) added a new structure
cchar_t to store the character, attributes and color-pair values,
allowing increased range of color-pairs. Both color-pairs and color-values
used a signed short, limiting values to 15 bits.
- •
- ncurses (1992-present) uses eight bits for A_COLOR
in chtype values.
- Version 5.3 provided a wide-character interface (2002), but
left color-pairs as part of the attributes-field.
- Since version 6 (2015), ncurses uses a separate int
for color-pairs in the cchar_t values. When those color-pair values
fit in 8 bits, ncurses allows color-pairs to be manipulated via the
functions using chtype values.
- •
- NetBSD curses used 6 bits from 2000 (when colors were first
supported) until 2004. At that point, NetBSD changed to use 10 bits. As of
2021, that size is unchanged. Like ncurses before version 6, the NetBSD
color-pair information is stored in the attributes field of
cchar_t, limiting the number of color-pairs by the size of the
bitfield.
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(3X) 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(3X)
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.
X/Open Curses does not specify a limit for the number of colors and color pairs
which a terminal can support. However, in its use of
short for the
parameters, it carries over SVr4's implementation detail for the compiled
terminfo database, which uses signed 16-bit numbers. This implementation
provides extended versions of those functions which use
short
parameters, allowing applications to use larger color- and pair-numbers.
The
reset_color_pairs function is an extension of ncurses.
ncurses(3NCURSES),
initscr(3NCURSES),
attr(3NCURSES),
curses_variables(3NCURSES),
default_colors(3NCURSES)