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.\" $Id: curs_color.3,v 1.11 2023/10/17 09:52:08 nicm Exp $
.TH curs_color 3 2023-07-01 "ncurses 6.4" "Library calls"
.ie \n(.g .ds `` \(lq
.el       .ds `` ``
.ie \n(.g .ds '' \(rq
.el       .ds '' ''
.de bP
.ie n  .IP \(bu 4
.el    .IP \(bu 2
..
.ds n 5
.na
.hy 0
.SH NAME
\fBstart_color\fP,
\fBhas_colors\fP,
\fBcan_change_color\fP,
\fBinit_pair\fP,
\fBinit_color\fP,
\fBinit_extended_pair\fP,
\fBinit_extended_color\fP,
\fBcolor_content\fP,
\fBpair_content\fP,
\fBextended_color_content\fP,
\fBextended_pair_content\fP,
\fBreset_color_pairs\fP,
\fBCOLOR_PAIR\fP,
\fBPAIR_NUMBER\fP \- \fBcurses\fP color manipulation routines
.ad
.hy
.SH SYNOPSIS
\fB#include <curses.h>\fP
.sp
\fBint start_color(void);\fP
.sp
\fBbool has_colors(void);\fP
.br
\fBbool can_change_color(void);\fP
.sp
\fBint init_pair(short \fIpair\fB, short \fIf\fB, short \fIb\fB);\fR
.br
\fBint init_color(short \fIcolor\fB, short \fIr\fB, short \fIg\fB, short \fIb\fB);\fR
.br
/* extensions */
.br
\fBint init_extended_pair(int \fIpair\fB, int \fIf\fB, int \fIb\fB);\fR
.br
\fBint init_extended_color(int \fIcolor\fB, int \fIr\fB, int \fIg\fB, int \fIb\fB);\fR
.sp
\fBint color_content(short \fIcolor\fB, short *\fIr\fB, short *\fIg\fB, short *\fIb\fB);\fR
.br
\fBint pair_content(short \fIpair\fB, short *\fIf\fB, short *\fIb\fB);\fR
.br
/* extensions */
.br
\fBint extended_color_content(int \fIcolor\fB, int *\fIr\fB, int *\fIg\fB, int *\fIb\fB);\fR
.br
\fBint extended_pair_content(int \fIpair\fB, int *\fIf\fB, int *\fIb\fB);\fR
.sp
/* extensions */
.br
\fBvoid reset_color_pairs(void);\fP
.sp
\fBint COLOR_PAIR(int \fIn\fB);\fR
.br
\fBPAIR_NUMBER(\fIattrs\fB);\fR
.SH DESCRIPTION
.SS Overview
\fBcurses\fP supports color attributes on terminals with that capability.
To use these routines \fBstart_color\fP must be called, usually right after
\fBinitscr\fP.
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\fP.
After it has been initialized, \fBCOLOR_PAIR\fP(\fIn\fP)
can be used to convert the pair to a video attribute.
.PP
If a terminal is capable of redefining colors, the programmer can use the
routine \fBinit_color\fP to change the definition of a color.
The routines \fBhas_colors\fP and \fBcan_change_color\fP
return \fBTRUE\fP or \fBFALSE\fP,
depending on whether the terminal has color capabilities and whether the
programmer can change the colors.
The routine \fBcolor_content\fP allows a
programmer to extract the amounts of red, green, and blue components in an
initialized color.
The routine \fBpair_content\fP 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 color pair 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.
.SH CONSTANTS
In \fB<curses.h>\fP the following macros are defined.
These are the standard colors (ISO-6429).
\fBcurses\fP also assumes that \fBCOLOR_BLACK\fP is the default
background color for all terminals.
.PP
.nf
      \fBCOLOR_BLACK\fP
      \fBCOLOR_RED\fP
      \fBCOLOR_GREEN\fP
      \fBCOLOR_YELLOW\fP
      \fBCOLOR_BLUE\fP
      \fBCOLOR_MAGENTA\fP
      \fBCOLOR_CYAN\fP
      \fBCOLOR_WHITE\fP
.fi
.PP
Some terminals support more than the eight (8) \*(``ANSI\*('' colors.
There are no standard names for those additional colors.
.SH VARIABLES
.SS COLORS
is initialized by \fBstart_color\fP to the maximum number of colors
the terminal can support.
.SS COLOR_PAIRS
is initialized by \fBstart_color\fP to the maximum number of color pairs
the terminal can support.
.SH FUNCTIONS
.SS start_color
The \fBstart_color\fP 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\fP.
\fBstart_color\fP does this:
.bP
It initializes two global variables, \fBCOLORS\fP and
\fBCOLOR_PAIRS\fP (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),
using weights that depend upon the CGA/HLS choice.
For \*(``ANSI\*('' colors the weights are \fB680\fP or \fB0\fP
depending on whether the corresponding
red, green, or blue component is used or not.
That permits using \fB1000\fP 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 \fB1000\fP.
SVr4 uses a similar scheme, but uses \fB1000\fP
for the components of the initial eight colors.
.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,
(see \fBterminfo\fP(\*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(3)).
.bP
\fBCOLOR_PAIRS\fP corresponds to
the terminal database's \fBmax_pairs\fP capability,
(see \fBterminfo\fP(\*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.
.SS has_colors
The \fBhas_colors\fP routine requires no arguments.
It returns \fBTRUE\fP if
the terminal can manipulate colors; otherwise, it returns \fBFALSE\fP.
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.
.SS can_change_color
The \fBcan_change_color\fP routine requires no arguments.
It returns \fBTRUE\fP if the terminal supports colors
and can change their definitions;
other, it returns \fBFALSE\fP.
This routine facilitates writing terminal-independent programs.
.SS init_pair
The \fBinit_pair\fP 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(3))
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\fP(3) routine, or to specify the use of
default colors (color number \fB\-1\fP) if you first invoke the
\fBuse_default_colors\fP(3) routine.
.SS init_extended_pair
Because \fBinit_pair\fP uses signed \fBshort\fPs for its parameters,
that limits color-pairs and color-values
to 32767 on modern hardware.
The extension \fBinit_extended_pair\fP uses \fBint\fPs
for the color-pair and color-value,
allowing a larger number of colors to be supported.
.SS init_color
The \fBinit_color\fP 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).
.bP
The first argument must be a legal color value;
default colors are not allowed here.
(See the section \fBColors\fP for the default color index.)
.bP
Each of the last three arguments
must be a value in the range \fB0\fP through \fB1000\fP.
.PP
When \fBinit_color\fP is used, all
occurrences of that color on the screen immediately change to the new
definition.
.SS init_extended_color
Because \fBinit_color\fP uses signed \fBshort\fPs for its parameters,
that limits color-values and their red, green, and blue components
to 32767 on modern hardware.
The extension \fBinit_extended_color\fP uses \fBint\fPs
for the color value and
for setting the red, green, and blue components,
allowing a larger number of colors to be supported.
.SS color_content
The \fBcolor_content\fP 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.
.bP
The first argument must be a legal color value, i.e.,
\fB0\fP through \fBCOLORS\-1\fP, inclusive.
.bP
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.
.SS extended_color_content
Because \fBcolor_content\fP uses signed \fBshort\fPs for its parameters,
that limits color-values and their red, green, and blue components
to 32767 on modern hardware.
The extension \fBextended_color_content\fP uses \fBint\fPs
for the color value and
for returning the red, green, and blue components,
allowing a larger number of colors to be supported.
.SS pair_content
The \fBpair_content\fP 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.
.bP
The first argument must be a legal color value,
i.e., in the range \fB1\fP through \fBCOLOR_PAIRS\-1\fP, inclusive.
.bP
The values that are stored at the addresses pointed
to by the second and third arguments are in the
range \fB0\fP through \fBCOLORS\fP, inclusive.
.SS extended_pair_content
Because \fBpair_content\fP uses signed \fBshort\fPs for its parameters,
that limits color-pair and color-values to 32767 on modern hardware.
The extension \fBextended_pair_content\fP uses \fBint\fPs
for the color pair and
for returning the foreground and background colors,
allowing a larger number of colors to be supported.
.SS reset_color_pairs
The extension \fBreset_color_pairs\fP tells ncurses to discard all
of the color-pair information which was set with \fBinit_pair\fP.
It also touches the current- and standard-screens, allowing an application to
switch color palettes rapidly.
.SS PAIR_NUMBER
\fBPAIR_NUMBER(\fIattrs\fR) extracts the color
value from its \fIattrs\fP parameter and returns it as a color pair number.
.SS COLOR_PAIR
Its inverse \fBCOLOR_PAIR(\fIn\fB)\fR 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 \fBattr_set\fP (which pass the color pair as a separate parameter)
rather than the legacy functions such as \fBattrset\fP.
.SH RETURN VALUE
The routines \fBcan_change_color\fP and \fBhas_colors\fP return \fBTRUE\fP
or \fBFALSE\fP.
.PP
All other routines return the integer \fBERR\fP upon failure and an \fBOK\fP
(SVr4 specifies only \*(``an integer value
other than \fBERR\fP\*('') upon successful completion.
.PP
X/Open defines no error conditions.
SVr4 does document some error conditions which apply in general:
.bP
This implementation will return \fBERR\fP on attempts to
use color values outside the range \fB0\fP to \fBCOLORS\fP\-1
(except for the default colors extension),
or use color pairs outside the range \fB0\fP to \fBCOLOR_PAIRS\-1\fP.
.IP
Color values used in \fBinit_color\fP must be
in the range \fB0\fP to \fB1000\fP.
.IP
An error is returned from all functions
if the terminal has not been initialized.
.IP
An error is returned from secondary functions such as \fBinit_pair\fP
if \fBstart_color\fP was not called.
.bP
SVr4 does much the same, except that
it returns \fBERR\fP from \fBpair_content\fP if the pair was not initialized
using \fBinit_pairs\fP
and
it returns \fBERR\fP from \fBcolor_content\fP
if the terminal does not support changing colors.
.IP
This implementation does not return \fBERR\fP for either case.
.PP
Specific functions make additional checks:
.RS 3
.TP 5
\fBinit_color\fP
returns an error if the terminal does not support
this feature, e.g., if the \fBinitialize_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 \fBncurses\fP implementation, there is a separate color activation flag,
color palette, color pairs table,
and associated \fBCOLORS\fP and \fBCOLOR_PAIRS\fP counts
for each screen; the \fBstart_color\fP 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
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\fP(3).
.PP
Several caveats apply on older x86 machines
(e.g., i386, i486) with VGA-compatible graphics:
.bP
COLOR_YELLOW is actually brown.
To get yellow, use COLOR_YELLOW combined with the \fBA_BOLD\fP 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 HISTORY
SVr3.2 introduced color support to curses in 1987.
.PP
SVr4 made internal changes,
e.g., moving the storage for the color state
from \fBSP\fP (the \fBSCREEN\fP structure)
to \fBcur_term\fP (the \fBTERMINAL\fP structure),
but provided the same set of library functions.
.PP
SVr4 curses limits the number of color pairs to 64,
reserving color pair zero (0) as the terminal's initial uncolored state.
This limit arises because the color pair information is a bitfield
in the \fBchtype\fP data type (denoted by \fBA_COLOR\fP).
.PP
Other implementations of curses had different limits:
.bP
PCCurses (1987-1990) provided for only eight (8) colors.
.bP
PDCurses (1992-present) inherited the 8-color limitation from PCCurses,
but changed this to 256 in version 2.5 (2001),
along with changing \fBchtype\fP from 16-bits to 32-bits.
.bP
X/Open Curses (1992-present)
added a new structure \fBcchar_t\fP to store the character,
attributes and color-pair values, allowing increased range of color-pairs.
Both color-pairs and color-values used a signed \fBshort\fP,
limiting values to 15 bits.
.bP
ncurses (1992-present) uses eight bits for \fBA_COLOR\fP in \fBchtype\fP values.
.IP
Version 5.3 provided a wide-character interface (2002),
but left color-pairs as part of the attributes-field.
.IP
Since version 6 (2015),
ncurses uses a separate \fBint\fP for color-pairs in the \fBcchar_t\fP values.
When those color-pair values fit in 8 bits,
ncurses allows color-pairs to be manipulated
via the functions using \fBchtype\fP values.
.bP
NetBSD curses used 6 bits from
2000 (when colors were first supported) until 2004.
At that point, NetBSD changed to use 10 bits.
As of 2021, that size is unchanged.
Like ncurses before version 6,
the NetBSD color-pair information is stored in
the attributes field of \fBcchar_t\fP, limiting the number of color-pairs
by the size of the bitfield.
.SH PORTABILITY
.SS Extensions
The functions marked as extensions were designed for \fBncurses\fP(3),
and are not found in SVr4 curses, 4.4BSD curses,
or any other previous version of curses.
.SS Standards
This implementation satisfies XSI Curses's minimum maximums
for \fBCOLORS\fP and \fBCOLOR_PAIRS\fP.
.PP
The \fBinit_pair\fP routine accepts negative values of foreground
and background color to support the \fBuse_default_colors\fP(3) extension,
but only if that routine has been first invoked.
.PP
The assumption that \fBCOLOR_BLACK\fP is the default
background color for all terminals can be modified using the
\fBassume_default_colors\fP(3) 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.
.PP
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 \fBshort\fP 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 \fBshort\fP parameters,
allowing applications to use larger color- and pair-numbers.
.PP
The \fBreset_color_pairs\fP function is an extension of ncurses.
.SH SEE ALSO
\fBcurses\fP(3),
\fBcurs_initscr\fP(3),
\fBcurs_attr\fP(3),
\fBcurs_variables\fP(3),
\fBdefault_colors\fP(3)