curs_color(3X)                                                curs_color(3X)

NAME         top

       start_color, has_colors, can_change_color, init_pair, init_color,
       color_content, pair_content, reset_color_pairs, COLOR_PAIR,
       PAIR_NUMBER - curses color manipulation routines

SYNOPSIS         top

       #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);

DESCRIPTION         top

       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.

   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.

CONSTANTS         top

       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.


       Some terminals support more than the eight (8) “ANSI” colors.  There
       are no standard names for those additional colors.

VARIABLES         top

       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.

FUNCTIONS         top

       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, (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, (see terminfo(5)).

       ·   legal color pair values are in the range 1 to COLOR_PAIRS-1,

       ·   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) 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

       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.

       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.

       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

       ·   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 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,

       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.

RETURN VALUE         top

       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.

               returns an error if the terminal does not support this
               feature, e.g., if the initialize_color capability is absent
               from the terminal description.

               returns an error if the color table cannot be allocated.

NOTES         top

       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.

PORTABILITY         top

       This implementation satisfies XSI Curses's minimum maximums for

       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)

       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.

SEE ALSO         top

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

COLOPHON         top

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