# 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 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 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.

### Color Rendering

           The curses library combines these inputs  to  produce  the
           actual  foreground  and  background  colors  shown  on the
           screen:

           o   per-character video attributes (e.g., via waddch),

           o   the window attribute (e.g., by wattrset), and

           o   the background character (e.g., wbkgdset).

           Per-character and window attributes are usually set  by  a
           parameter  containing  video  attributes  including a COL-
           OR_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:

           o   If the parameter passed to waddch is blank, and it us-
               es 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 at-
                   tribute.

               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 fi-
               nally the background character.

           Some curses functions such as wprintw call waddch.   Those
           do  not  combine  its parameter with a color pair.  Conse-
           quently those calls use only the window attribute  or  the
           background character.

### 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 does this:

           o   It  initializes  two global variables, COLORS and COL-
               OR_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_sat-
               uration) capability is set).  The table is initialized
               first for eight basic colors (black, red, green,  yel-
               low,  blue,  magenta, cyan, and white), and after that
               (if the terminal supports more than eight colors)  the
               components are initialized to 1000.

               start_color  does  not  attempt  to set the terminal's
               color palette to match its built-in table.  An  appli-
               cation  may use init_color to alter the internal table
               along with the terminal's color.

           These limits apply to color values and color pairs.   Val-
           ues  outside these limits are not legal, and may result in
           a runtime error:

           o   COLORS corresponds to the terminal database's max_col-
               ors capability, which is typically a signed 16-bit in-
               teger (see terminfo(5)).

           o   color values are expected to be in the range 0 to COL-
               ORS-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_de-
               fault_colors).

           o   COLOR_PAIRS  corresponds  to  the  terminal database's
               max_pairs capability,  which  is  typically  a  signed
               16-bit integer (see terminfo(5)).

           o   legal  color  pair  values  are in the range 1 to COL-
               OR_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 applica-
               tion.

           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 legal color  pair  value.
               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 back-
               ground.

           o   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 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 first argument must
           be a legal color value; default  colors  are  not  allowed
           here.   (See  the section Colors for the default color in-
           dex.)  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.

           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 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.

           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, inclu-
           sive.  The values that are stored at the addresses pointed
           to  by  the  second and third arguments are in the range 0
           through COLORS, inclusive.

### Colors

           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 termi-
           nals.

                 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)