.\"***************************************************************************
.\" Copyright (c) 1998-2010,2015 Free Software Foundation, Inc.              *
.\"                                                                          *
.\" Permission is hereby granted, free of charge, to any person obtaining a  *
.\" copy of this software and associated documentation files (the            *
.\" "Software"), to deal in the Software without restriction, including      *
.\" without limitation the rights to use, copy, modify, merge, publish,      *
.\" distribute, distribute with modifications, sublicense, and/or sell       *
.\" copies of the Software, and to permit persons to whom the Software is    *
.\" furnished to do so, subject to the following conditions:                 *
.\"                                                                          *
.\" The above copyright notice and this permission notice shall be included  *
.\" in all copies or substantial portions of the Software.                   *
.\"                                                                          *
.\" THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS  *
.\" OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF               *
.\" MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.   *
.\" IN NO EVENT SHALL THE ABOVE COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,   *
.\" DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR    *
.\" OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR    *
.\" THE USE OR OTHER DEALINGS IN THE SOFTWARE.                               *
.\"                                                                          *
.\" Except as contained in this notice, the name(s) of the above copyright   *
.\" holders shall not be used in advertising or otherwise to promote the     *
.\" sale, use or other dealings in this Software without prior written       *
.\" authorization.                                                           *
.\"***************************************************************************
.\"
.\" $Id: curs_color.3x,v 1.39 2015/06/06 23:29:02 tom Exp $
.TH curs_color 3X ""
.ie \n(.g .ds `` \(lq
.el       .ds `` ``
.ie \n(.g .ds '' \(rq
.el       .ds '' ''
.de bP
.IP \(bu 4
..
.ds n 5
.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 supports 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 Color Rendering
The \fBcurses\fP library combines these inputs to produce the
actual foreground and background colors shown on the screen:
.bP
per-character video attributes (e.g., via \fBwaddch\fP),
.bP
the window attribute (e.g., by \fBwattrset\fP), and
.bP
the background character (e.g., \fBwbkgdset\fP).
.PP
Per-character and window attributes are usually set by a parameter containing
video attributes including a \fBCOLOR_PAIR\fP value.
Some functions such as \fBwattr_set\fP use a separate parameter which
is the color pair number.
.PP
The background character is a special case: it includes a character value,
just as if it were passed to \fBwaddch\fP.
.PP
The \fBcurses\fP library does the actual work of combining these color
pairs in an internal function called from \fBwaddch\fP:
.bP
If the parameter passed to \fBwaddch\fP is \fIblank\fP,
and it uses the special color pair 0,
.RS
.bP
\fBcurses\fP next checks the window attribute.
.bP
If the window attribute does not use color pair 0,
\fBcurses\fP uses the color pair from the window attribute.
.bP
Otherwise, \fBcurses\fP uses the background character.
.RE
.bP
If the parameter passed to \fBwaddch\fP is \fInot blank\fP,
or it does not use the special color pair 0,
\fBcurses\fP prefers the color pair from the parameter,
if it is nonzero.
Otherwise, it tries the window attribute next, and finally the
background character.
.PP
Some \fBcurses\fP functions such as \fBwprintw\fP call \fBwaddch\fP.
Those do not combine its parameter with a color pair.
Consequently those calls use only the window attribute or
the background character.
.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 does this:
.bP
It initializes two global variables, \fBCOLORS\fR and
\fBCOLOR_PAIRS\fR (respectively defining the maximum number of colors
and color-pairs the terminal can support).
.bP
It initializes the special color pair \fB0\fP to the default foreground
and background colors.
No other color pairs are initialized.
.bP
It restores the colors on the terminal to the values
they had when the terminal was just turned on.
.bP
If the terminal supports the \fBinitc\fP (\fBinitialize_color\fP) capability,
\fBstart_color\fP
initializes its internal table representing the
red, green and blue components of the color palette.
.IP
The components depend on whether the terminal uses
CGA (aka "ANSI") or
HLS (i.e., the \fBhls\fP (\fBhue_lightness_saturation\fP) capability is set).
The table is initialized first for eight basic colors
(black, red, green, yellow, blue, magenta, cyan, and white),
and after that (if the terminal supports more than eight colors)
the components are initialized to \fB1000\fP.
.IP
\fBstart_color\fP does not attempt to set the terminal's color palette
to match its built-in table.
An application may use \fBinit_color\fP to alter the internal table
along with the terminal's color.
.PP
These limits apply to color values and color pairs.
Values outside these limits are not legal, and may result in a runtime error:
.bP
\fBCOLORS\fP corresponds to the terminal database's \fBmax_colors\fP capability,
which is typically a signed 16-bit integer (see \fBterminfo\fR(\*n)).
.bP
color values are expected to be in the range \fB0\fP to \fBCOLORS\-1\fP,
inclusive (including \fB0\fP and \fBCOLORS\-1\fP).
.bP
a special color value \fB\-1\fP is used in certain extended functions
to denote the \fIdefault color\fP (see \fBuse_default_colors\fP).
.bP
\fBCOLOR_PAIRS\fP corresponds to the terminal database's \fBmax_pairs\fP capability,
which is typically a signed 16-bit integer (see \fBterminfo\fR(\*n)).
.bP
legal color pair values are in the range \fB1\fP to \fBCOLOR_PAIRS\-1\fP,
inclusive.
.bP
color pair \fB0\fP is special; it denotes \*(``no color\*(''.
.IP
Color pair \fB0\fP 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
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 first argument must be a legal color pair value.
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 second and third arguments must be legal color values.
.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 \fB0\fP 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 first argument must be a legal color value;
default colors are not allowed here.
(See the section \fBColors\fR for the default color index.)
Each of the last three arguments
must be a value in the range \fB0\fP through \fB1000\fP.
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 first argument must be a legal color value, i.e.,
\fB0\fP through \fBCOLORS\-1\fP, inclusive.
The values that are stored at the addresses pointed to by the
last three arguments are in the range
\fB0\fP (no component) through \fB1000\fP (maximum amount of component), inclusive.
.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 first argument must be a legal color value,
i.e., in the range \fB1\fP through \fBCOLOR_PAIRS\-1\fR, inclusive.
The values that are stored at the addresses pointed
to by the second and third arguments are in the
range \fB0\fP through \fBCOLORS\fR, inclusive.
.SS Colors
In \fB<curses.h>\fR the following macros are defined.
These are the standard colors (ISO-6429).
\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 \fB0\fP to COLORS\-1
(except for the default colors extension),
or use color pairs outside the range \fB0\fP to \fBCOLOR_PAIRS\-1\fP.
Color values used in \fBinit_color\fP must be in the range \fB0\fP to \fB1000\fP.
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)