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curs_color(3)                   Library calls                  curs_color(3)


NAME

       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

       #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);


DESCRIPTION

   Overview
       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.

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

       o   curses character attributes, as from waddch(3X) or wadd_wch(3X)

       o   window attributes, as from wattrset(3X) or wattr_set(3X)

       o   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:

       o   If the parameter passed to waddch is blank, and it uses the special
           color pair 0,

           o   curses next checks the window attribute.

           o   If the window attribute does not use color pair 0, curses uses
               the color pair from the window attribute.

           o   Otherwise, curses uses the background character.

       o   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

       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

   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.  Often, its value is the product COLORS x COLORS,
       but this is not always true.

       o   A few terminals use the HLS color space (see start_color below),
           ignoring this rule; and

       o   terminals supporting a large number of colors are limited to the
           number of color pairs that a signed short value can represent.


FUNCTIONS

   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:

       o   It initializes two global variables, COLORS and COLOR_PAIRS
           (respectively defining the maximum number of colors and color pairs
           the terminal can support).

       o   It initializes the special color pair 0 to the default foreground
           and background colors.  No other color pairs are initialized.

       o   It restores the colors on the terminal to the values they had when
           the terminal was just turned on.

       o   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:

       o   COLORS corresponds to the terminal database's max_colors
           capability, (see terminfo(5)).

       o   color values are expected to be in the range 0 to COLORS-1,
           inclusive (including 0 and COLORS-1).

       o   a special color value -1 is used in certain extended functions to
           denote the default color (see use_default_colors(3X)).

       o   COLOR_PAIRS corresponds to the terminal database's max_pairs
           capability, (see terminfo(5)).

       o   valid color pair values are in the range 1 to COLOR_PAIRS-1,
           inclusive.

       o   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:

       o   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.

       o   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.

   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).

       o   The first argument must be a valid color value; default colors are
           not allowed here.  (See the section Colors for the default color
           index.)

       o   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.

       o   The first argument must be a valid color value, i.e., 0 through
           COLORS-1, inclusive.

       o   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.

       o   The first argument must be a valid color value, i.e., in the range
           1 through COLOR_PAIRS-1, inclusive.

       o   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.

   COLOR_PAIR
       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
       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.


RETURN VALUE

       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:

       o   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.

       o   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

       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:

       o   COLOR_YELLOW is actually brown.  To get yellow, use COLOR_YELLOW
           combined with the A_BOLD attribute.

       o   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).

       o   Color RGB values are not settable.


EXTENSIONS

       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.


PORTABILITY

       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.


HISTORY

       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:

       o   PCCurses (1987-1990) provided for only eight (8) colors.

       o   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.

       o   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.

       o   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.

       o   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.


SEE ALSO

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

ncurses 6.5                       2024-04-20                    curs_color(3)

ncurses 6.5 - Generated Wed May 1 12:40:51 CDT 2024
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