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curs_color(3)                                                  curs_color(3)




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  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),  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 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(3X)).

       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(3X)) the upper limit is ad-
           justed to allow for extra pairs which use a default color in  fore-
           ground 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.

   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 exten-
       sion 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).

       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.

   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 mod-
       ern hardware.  The extension init_extended_color uses ints for the col-
       or 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  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.

   extended_color_content
       Because color_content uses signed shorts for its parameters, that  lim-
       its  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.

       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.

   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 col-
       ors 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 com-
       pletion.

       X/Open defines no error conditions.  SVr4 does document some error con-
       ditions which apply in general:

       o   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 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.

       o   SVr4 does much the same, except that it returns ERR from  pair_con-
           tent  if  the  pair was not initialized using init_pairs and it re-
           turns 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  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(3)



                                                                curs_color(3)

ncurses 6.2 - Generated Sun Feb 16 15:36:20 CST 2020
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