# curs_color 3x 2023-12-30 ncurses 6.4 Library calls

    curs_color(3x)                   Library calls                  curs_color(3x)

## 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 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.

## 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 6.4                       2023-12-30                    curs_color(3x)