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curs_color(3X)							curs_color(3X)

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:

          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 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:

          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 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:

          It  initializes  two	 global	variables, COLORS and COLOR_PAIRS (re-
	   spectively 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 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:

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

          color  values are expected to be in the range 0 to COLORS-1,	inclu-
	   sive	(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 capa-
	   bility, (see	terminfo(5)).

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

          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:

          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.

          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).

          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 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.

          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 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.

          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  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:

          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.

          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:

          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 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)

NAME | SYNOPSIS | DESCRIPTION | CONSTANTS | VARIABLES | FUNCTIONS | RETURN VALUE | NOTES | PORTABILITY | SEE ALSO

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