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.\" $Id: curs_color.3x,v 1.35 2010/12/20 00:50:58 tom Exp $
.TH curs_color 3X ""
.de bP
.IP \(bu 4
..
.na
.hy 0
.SH NAME
\fBstart_color\fR,
\fBinit_pair\fR,
\fBinit_color\fR,
\fBhas_colors\fR,
\fBcan_change_color\fR,
\fBcolor_content\fR,
\fBpair_content\fR,
\fBCOLOR_PAIR\fR \- \fBcurses\fR color manipulation routines
.ad
.hy
.SH SYNOPSIS
\fB# include <curses.h>\fR
.sp
\fBint start_color(void);\fR
.br
\fBint init_pair(short pair, short f, short b);\fR
.br
\fBint init_color(short color, short r, short g, short b);\fR
.br
\fBbool has_colors(void);\fR
.br
\fBbool can_change_color(void);\fR
.br
\fBint color_content(short color, short *r, short *g, short *b);\fR
.br
\fBint pair_content(short pair, short *f, short *b);\fR
.br
.SH DESCRIPTION
.SS Overview
\fBcurses\fR support color attributes on terminals with that capability.  To
use these routines \fBstart_color\fR must be called, usually right after
\fBinitscr\fR.  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 \fBinit_pair\fR.  After it
has been initialized, \fBCOLOR_PAIR\fR(\fIn\fR), a macro defined in
\fB<curses.h>\fR, can be used as a new video attribute.
.PP
If a terminal is capable of redefining colors, the programmer can use the
routine \fBinit_color\fR to change the definition of a color.  The routines
\fBhas_colors\fR and \fBcan_change_color\fR return \fBTRUE\fR or \fBFALSE\fR,
depending on whether the terminal has color capabilities and whether the
programmer can change the colors.  The routine \fBcolor_content\fR allows a
programmer to extract the amounts of red, green, and blue components in an
initialized color.  The routine \fBpair_content\fR allows a programmer to find
out how a given color-pair is currently defined.
.SS Routine Descriptions
The \fBstart_color\fR 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 \fBinitscr\fR.  \fBstart_color\fR initializes
eight basic colors (black, red, green, yellow, blue, magenta, cyan,
and white), and two global variables, \fBCOLORS\fR and
\fBCOLOR_PAIRS\fR (respectively defining the maximum number of colors
and color-pairs the terminal can support).  It also restores the
colors on the terminal to the values they had when the terminal was
just turned on.
.PP
The \fBinit_pair\fR 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:
.bP
The value of the first argument
must be between \fB1\fR and \fBCOLOR_PAIRS\-1\fR,
except that if default colors are used (see \fBuse_default_colors\fP)
the upper limit is adjusted to allow for extra pairs which use
a default color in foreground and/or background.
.bP
The value of the second and
third arguments must be between 0 and \fBCOLORS\fR.
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.
.PP
If the color-pair was previously
initialized, the screen is refreshed and all occurrences of that color-pair
are changed to the new definition.
.PP
As an extension, ncurses allows you to set color pair 0 via
the \fBassume_default_colors\fR routine, or to specify the use of
default colors (color number \fB\-1\fR) if you first invoke the
\fBuse_default_colors\fR routine.
.PP
The \fBinit_color\fR 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 value of the first
argument must be between \fB0\fR and \fBCOLORS\fR.  (See the section
\fBColors\fR for the default color index.)  Each of the last three arguments
must be a value between 0 and 1000.  When \fBinit_color\fR is used, all
occurrences of that color on the screen immediately change to the new
definition.
.PP
The \fBhas_colors\fR routine requires no arguments.  It returns \fBTRUE\fR if
the terminal can manipulate colors; otherwise, it returns \fBFALSE\fR.  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.
.PP
The \fBcan_change_color\fR routine requires no arguments.  It returns
\fBTRUE\fR if the terminal supports colors and can change their definitions;
other, it returns \fBFALSE\fR.  This routine facilitates writing
terminal-independent programs.
.PP
The \fBcolor_content\fR 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 \fBshort\fRs for storing
the information about the amounts of red, green, and blue components in the
given color.  The value of the first argument must be between 0 and
\fBCOLORS\fR.  The values that are stored at the addresses pointed to by the
last three arguments are between 0 (no component) and 1000 (maximum amount of
component).
.PP
The \fBpair_content\fR 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 \fBshort\fRs for storing the foreground and the
background color numbers.  The value of the first argument must be between 1
and \fBCOLOR_PAIRS\-1\fR.  The values that are stored at the addresses pointed
to by the second and third arguments are between 0 and \fBCOLORS\fR.
.SS Colors
In \fB<curses.h>\fR the following macros are defined.  These are the default
colors.  \fBcurses\fR also assumes that \fBCOLOR_BLACK\fR is the default
background color for all terminals.
.PP
.nf
      \fBCOLOR_BLACK\fR
      \fBCOLOR_RED\fR
      \fBCOLOR_GREEN\fR
      \fBCOLOR_YELLOW\fR
      \fBCOLOR_BLUE\fR
      \fBCOLOR_MAGENTA\fR
      \fBCOLOR_CYAN\fR
      \fBCOLOR_WHITE\fR
.fi
.SH RETURN VALUE
The routines \fBcan_change_color()\fR and \fBhas_colors()\fR return \fBTRUE\fR
or \fBFALSE\fR.
.PP
All other routines return the integer \fBERR\fR upon failure and an \fBOK\fR
(SVr4 specifies only "an integer value other than \fBERR\fR") upon successful
completion.
.PP
X/Open defines no error conditions.
This implementation will return \fBERR\fR 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 \fBinit_color\fP 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 \fBinit_pair\fP
if \fBstart_color\fP was not called.
.RS 3
.TP 5
\fBinit_color\fP
returns an error if the terminal does not support
this feature, e.g., if the \fIinitialize_color\fP capability is absent
from the terminal description.
.TP 5
\fBstart_color\fP
returns an error if the color table cannot be allocated.
.RE
.SH NOTES
In the \fIncurses\fR implementation, there is a separate color activation flag,
color palette, color pairs table, and associated COLORS and COLOR_PAIRS counts
for each screen; the \fBstart_color\fR 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.
.PP
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 \fBcurs_bkgd\fR(3X).
.PP
Several caveats apply on 386 and 486 machines with VGA-compatible graphics:
.bP
COLOR_YELLOW is actually brown.  To get yellow, use COLOR_YELLOW combined with
the \fBA_BOLD\fR attribute.
.bP
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).
.bP
Color RGB values are not settable.
.SH PORTABILITY
This implementation satisfies XSI Curses's minimum maximums
for \fBCOLORS\fR and \fBCOLOR_PAIRS\fR.
.PP
The \fBinit_pair\fP routine accepts negative values of foreground
and background color to support the \fBuse_default_colors\fP extension,
but only if that routine has been first invoked.
.PP
The assumption that \fBCOLOR_BLACK\fR is the default
background color for all terminals can be modified using the
\fBassume_default_colors\fP extension.
.PP
This implementation checks the pointers,
e.g., for the values returned by
\fBcolor_content\fP and \fBpair_content\fP,
and will treat those as optional parameters when null.
.SH SEE ALSO
\fBcurses\fR(3X),
\fBcurs_initscr\fR(3X),
\fBcurs_attr\fR(3X),
\fBcurs_variables\fR(3X),
\fBdefault_colors\fR(3X)