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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  default colors.  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


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)