Provided by: ncurses-doc_6.1+20190803-1ubuntu1_all bug

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 - 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), 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
       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(3X)).

       ·   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(3X)) 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.

   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).

       ·   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.

   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.

       ·   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.

   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.

       ·   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.

   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.

   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.  SVr4 does document some error conditions which apply
       in general:

       ·   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.

       ·   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 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)