Manual Pages  — curs_color

 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,  COLORS,  COLOR_PAIRS,  COLOR_BLACK,  COLOR_RED,  COLOR_GREEN,  COLOR_YELLOW,  COLOR_BLUE,  COLOR_MAGENTA,  COLOR_CYAN,  COLOR_WHITE - manipulate terminal colors with curses

SYNOPSIS DESCRIPTION Overview Rendering CONSTANTS VARIABLES COLORS COLOR_PAIRS FUNCTIONS start_color has_colors can_change_color init_pair init_extended_pair init_color init_extended_color color_content extended_color_content pair_content extended_pair_content reset_color_pairs COLOR_PAIR PAIR_NUMBER RETURN VALUE NOTES EXTENSIONS PORTABILITY HISTORY SEE ALSO

#include <curses.h>

/* variables */
int COLOR_PAIRS;
int COLORS;

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);

/* extension */
void reset_color_pairs(void);

int COLOR_PAIR(int n);
PAIR_NUMBER(int attr);

curses supports color attributes on terminals with that capability. Call  start_color (typically right after  initscr(3X)) to enable this feature. Colors are always used in pairs. A color pair couples a foreground color for characters with a background color for the blank field on which characters are rendered.  init_pair initializes a color pair. The macro  COLOR_PAIR(n) can then convert the pair to a video attribute.

If a terminal has the relevant capability,  init_color permits (re)definition of a color.  has_colors and  can_change_color return TRUE or FALSE, depending on whether the terminal has color capability and whether the programmer can change the colors.  color_content permits extraction of the red, green, and blue components of an initialized color.  pair_content permits discovery of a color pair's current definition.

curses combines the following data to render a character cell. Any of them can include color information.

»	curses character attributes, as from  waddch(3X) or  wadd_wch(3X)
»	window attributes, as from  wattrset(3X) or  wattr_set(3X)
»	window background character attributes, as from  wbkgdset(3X) or  wbkgrndset(3X)

Per-character and window attributes are usually set through a function parameter containing attributes including a color pair value. Some functions, such as  wattr_set, use a separate color pair number parameter.

The background character is a special case: it includes a character code, 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. Often, its value is the product  COLORS &#181;  COLORS, but this is not always true.

»	A few terminals use the HLS color space (see  start_color below), ignoring this rule; and
»	terminals supporting a large number of colors are limited to the number of color pairs that a signed short value can represent.

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 valid, 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)).
»	valid 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 valid 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 valid 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 valid 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 valid 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 valid 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.

 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.

 PAIR_NUMBER(attr) extracts the color information from its attr parameter and returns it as a color pair number; it is the inverse operation of  COLOR_PAIR.

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  curs_bkgd(3X).

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.

The functions marked as extensions were designed for  ncurses(3X), and are not found in SVr4 curses, 4.4BSD curses, or any other previous curses implementation.

Applications employing  ncurses extensions should condition their use on the visibility of the  NCURSES_VERSION preprocessor macro.

This implementation satisfies X/Open 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.

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.

 curses(3X),  curs_attr(3X),  curs_initscr(3X),  curs_variables(3X),  default_colors(3X)