curs_color(3x) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | CONSTANTS | VARIABLES | FUNCTIONS | RETURN VALUE | NOTES | PORTABILITY | SEE ALSO | COLOPHON

curs_color(3X)                                            curs_color(3X)

NAME         top

       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

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);
       PAIR_NUMBER(attrs);

DESCRIPTION         top

   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) 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.

             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.

VARIABLES         top

   COLORS
       is initialized by start_color to the maximum number of colors the
       terminal can support.

   COLOR_PAIRS
       is initialized by start_color to the maximum number of color
       pairs the terminal can support.

FUNCTIONS         top

   start_color
       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.

   has_colors
       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.

   can_change_color
       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.

   init_pair
       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.

   init_extended_pair
       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.

   init_color
       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.

   init_extended_color
       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.

   color_content
       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.

   extended_color_content
       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.

   pair_content
       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.

   extended_pair_content
       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.

   reset_color_pairs
       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
       PAIR_NUMBER(attrs) extracts the color value from its attrs
       parameter and returns it as a color pair number.

   COLOR_PAIR
       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.  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.

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
       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.

SEE ALSO         top

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

COLOPHON         top

       This page is part of the ncurses (new curses) project.
       Information about the project can be found at 
       ⟨https://www.gnu.org/software/ncurses/ncurses.html⟩.  If you have
       a bug report for this manual page, send it to
       bug-ncurses-request@gnu.org.  This page was obtained from the
       project's upstream Git mirror of the CVS repository
       ⟨git://ncurses.scripts.mit.edu/ncurses.git⟩ on 2021-04-01.  (At
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                                                          curs_color(3X)