# curs_color 3x

    curs_color(3x)                                                  curs_color(3x)

## NAME

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

## SYNOPSIS

           #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

### 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 characters are dis-
           played).  A  programmer  initializes  a  color-pair  with  the  routine
           init_pair.  After it has been initialized, 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 rou-
           tines has_colors and can_change_color return TRUE or  FALSE,  depending
           on whether the terminal has color capabilities and whether the program-
           mer can change the colors.  The routine color_content allows a program-
           mer  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 fore-
           ground 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 con-
           taining  video attributes including a color pair value.  Some functions
           such as wattr_set use a separate parameter which is the color pair num-
           ber.

           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 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 at-
               tribute next, and finally the background character.

           Some curses functions such as wprintw call waddch.  Those do  not  com-
           bine its parameter with a color pair.  Consequently those calls use on-
           ly 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 ter-
           minal can support.

### COLOR_PAIRS

           is initialized by start_color to the maximum number of color pairs  the
           terminal can support.

## 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  manipu-
           lation  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  (re-
               spectively  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), 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 application may use init_color to al-
               ter the internal table along with the terminal's color.

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

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

           o   color  values are expected to be in the range 0 to COLORS-1, inclu-
               sive (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).

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

           o   legal color pair values are in the range 1 to COLOR_PAIRS-1, inclu-
               sive.

           o   color pair 0 is special; it denotes "no color".

               Color pair 0 is assumed to be white on black, but is actually what-
               ever the terminal implements before color is initialized.  It  can-
               not 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 rou-
           tine 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-indepen-
           dent 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 fore-
           ground color number, and the background color number.  For portable ap-
           plications:

           o   The  first  argument  must be a legal color pair value.  If default
               colors are used (see use_default_colors) the upper limit is adjust-
               ed to allow for extra pairs which use a default color in foreground
               and/or background.

           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 defini-
           tion.

           As an extension, ncurses allows you to set color pair  0  via  the  as-
           sume_default_colors(3x)  routine, or to specify the use of default col-
           ors (color number -1) if you first  invoke  the  use_default_colors(3x)
           routine.

           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.

### 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 legal 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.

### 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 com-
           ponents in the given color.

           o   The first argument must be a legal 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.

### 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 legal 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 sec-
               ond and third arguments are in the range 0 through  COLORS,  inclu-
               sive.

### PAIR_NUMBER

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

### COLOR_PAIR

           Its inverse 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.

## 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 com-
           pletion.

           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 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.

              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 COL-
           OR_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.

## PORTABILITY

           This implementation satisfies XSI Curses's minimum maximums for  COLORS
           and COLOR_PAIRS.

           The  init_pair  routine accepts negative values of foreground and back-
           ground 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)  exten-
           sion.

           This  implementation checks the pointers, e.g., for the values returned
           by color_content and pair_content, and will treat those as optional pa-
           rameters 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.

## SEE ALSO

           curses(3x),  curs_initscr(3x),  curs_attr(3x),  curs_variables(3x), de-
           fault_colors(3x)

                                                                    curs_color(3x)