Provided by: ncurses-doc_6.1+20181013-2ubuntu2_all bug

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
       displayed).   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  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 color_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:

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

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

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

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

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

           ·   curses next checks the window attribute.

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

           ·   Otherwise, curses uses the background character.

       ·   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.

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:

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

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

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

       ·   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 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
       legal, and may result in a runtime error:

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

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

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

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

       ·   legal color pair values are in the range 1 to COLOR_PAIRS-1, inclusive.

       ·   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:

       ·   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 background.

       ·   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(3X)
       routine, or to specify the use of default colors (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).

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

       ·   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 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.

   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.

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

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

   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 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
       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  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 bkgd(3NCURSES).

       Several  caveats  apply  on  older  x86  machines  (e.g.,  i386, i486) with VGA-compatible
       graphics:

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

       ·   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).

       ·   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  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.

SEE ALSO

       ncurses(3NCURSES),    initscr(3NCURSES),    attr(3NCURSES),    curses_variables(3NCURSES),
       default_colors(3NCURSES)

                                                                                  color(3NCURSES)