curs_color(3x) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | CONSTANTS | VARIABLES | FUNCTIONS | RETURN VALUE | NOTES | HISTORY | 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 capabili‐
       ty.   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  ini‐
       tialized,  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 parame‐
       ter 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 charac‐
       ter 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 col‐
           or-pairs the terminal can support).

       •   It initializes the special color pair 0 to the default fore‐
           ground and background colors.  No other color pairs are ini‐
           tialized.

       •   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) capa‐
           bility, start_color initializes its internal table represent‐
           ing 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) ca‐
           pability 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 termi‐
           nal's color.

       These limits apply to color values and color pairs.  Values out‐
       side these limits are not legal, and may result in a runtime er‐
       ror:

       •   COLORS corresponds to the terminal database's max_colors ca‐
           pability, (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 func‐
           tions to denote the default color (see use_default_col‐
           ors(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 defini‐
       tions; 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 de‐
           fault colors are used (see use_default_colors(3X)) the upper
           limit is adjusted to allow for extra pairs which use a de‐
           fault 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 re‐
       freshed 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 de‐
       fault colors (color number -1) if you first invoke the use_de‐
       fault_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 fol‐
       lowed by three RGB values (for the amounts of red, green, and
       blue components).

       •   The first argument must be a legal color value; default col‐
           ors 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 in‐
       tensity 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 col‐
       ors 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 applica‐
       tion to switch color palettes rapidly.

   PAIR_NUMBER
       PAIR_NUMBER(attrs) extracts the color value from its attrs para‐
       meter and returns it as a color pair number.

   COLOR_PAIR
       Its inverse COLOR_PAIR(n) converts a color pair number to an at‐
       tribute.  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 parame‐
       ter) 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 suc‐
       cessful completion.

       X/Open defines no error conditions.  SVr4 does document some er‐
       ror 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 de‐
           fault 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 ab‐
               sent 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 activa‐
       tion flag, color palette, color pairs table, and associated COL‐
       ORS and COLOR_PAIRS counts for each screen; the start_color func‐
       tion only affects the current screen.  The SVr4/XSI interface is
       not really designed with this in mind, and historical implementa‐
       tions may use a single shared color palette.

       Setting an implicit background color via a color pair affects on‐
       ly 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 COL‐
           OR_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 compati‐
           bles) do the wrong thing when you try to set a bright “yel‐
           low” background (you get a blinking yellow foreground in‐
           stead).

       •   Color RGB values are not settable.

HISTORY         top

       SVr3.2 introduced color support to curses in 1987.

       SVr4 made internal changes, e.g., moving the storage for the col‐
       or 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 bit‐
       field 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, allow‐
           ing 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 col‐
           or-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.

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_col‐
       ors(3X) extension.

       This implementation checks the pointers, e.g., for the values re‐
       turned 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 implemen‐
       tation 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.  Informa‐
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       a bug report for this manual page, send it to
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       ⟨https://github.com/mirror/ncurses.git⟩ on 2024-06-14.  (At that
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                                                          curs_color(3X)