# curs_color 3x

    curs_color(3x)                                           curs_color(3x)

## NAME

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

## SYNOPSIS

           # include <curses.h>

           int start_color(void);
           int init_pair(short pair, short f, short b);
           int init_color(short color, short r, short g, short b);
           bool has_colors(void);
           bool can_change_color(void);
           int  color_content(short  color, short *r, short *g, short
           *b);
           int pair_content(short pair, short *f, short *b);

## DESCRIPTION

       Overview
           curses support color attributes on terminals with that ca-
           pability.   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 charac-
           ters are displayed).  A programmer  initializes  a  color-
           pair  with  the routine init_pair.  After it has been ini-
           tialized, COLOR_PAIR(n), a macro  defined  in  <curses.h>,
           can be used as a new video attribute.

           If  a  terminal  is capable of redefining colors, the pro-
           grammer can use the routine init_color to change the defi-
           nition   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  col-
           or_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.

       Routine Descriptions
           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 initializes eight basic  colors  (black,  red,
           green,  yellow,  blue,  magenta, cyan, and white), and two
           global variables,  COLORS  and  COLOR_PAIRS  (respectively
           defining  the maximum number of colors and color-pairs the
           terminal can support).  It also restores the colors on the
           terminal to the values they had when the terminal was just
           turned on.

           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  value of the first argument must be between 1 and
               COLOR_PAIRS-1, except that 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.

           o   The  value  of  the second and third arguments must be
               between 0 and COLORS.  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.

           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 routine, or to  specify  the
           use  of  default colors (color number -1) if you first in-
           voke the use_default_colors routine.

           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 value of the first
           argument must be between 0 and COLORS.  (See  the  section
           Colors  for  the  default  color index.)  Each of the last
           three arguments must be a value between 0 and 1000.   When
           init_color  is  used, all occurrences of that color on the
           screen immediately change to the new definition.

           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  at-
           tribute.

           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 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 value of the first argument must be
           between 0 and COLORS.  The values that are stored  at  the
           addresses  pointed  to by the last three arguments are be-
           tween 0 (no component) and 1000 (maximum amount of  compo-
           nent).

           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  value of the first argument must be
           between 1 and COLOR_PAIRS-1.  The values that  are  stored
           at  the addresses pointed to by the second and third argu-
           ments are between 0 and COLORS.

       Colors
           In <curses.h> the following macros are defined.  These are
           the  default colors.  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

## 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.  This implementation
           will return ERR on attempts to use  color  values  outside
           the range 0 to COLORS-1 (except for the default colors ex-
           tension), or use color pairs outside the range 0  to  COL-
           OR_PAIRS-1.   Color  values  used in init_color must be in
           the range 0 to 1000.  An error is returned from all  func-
           tions  if the terminal has not been initialized.  An error
           is returned from secondary functions such as init_pair  if
           start_color was not called.

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

              start_color
                   returns  an error if the color table cannot be al-
                   located.

## NOTES

           In the ncurses implementation, there is a  separate  color
           activation flag, color palette, color pairs table, and as-
           sociated 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.

           Note that 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 386 and 486  machines  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 back-
               ground  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.

## PORTABILITY

           This  implementation  satisfies XSI Curses's minimum maxi-
           mums for COLORS and COLOR_PAIRS.

           The init_pair routine accepts  negative  values  of  fore-
           ground   and  background  color  to  support  the  use_de-
           fault_colors 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  as-
           sume_default_colors 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.

## SEE ALSO

           curses(3x),  curs_initscr(3x),  curs_attr(3x),  curs_vari-
           ables(3x), default_colors(3x)

                                                             curs_color(3x)