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 */
If a terminal is capable of redefining colors, the programmer can use the routine init_color to change the definition 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 color_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.
Per-character and window attributes are usually set by a parameter containing video attributes including a color 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:
.IP • 4 If the parameter passed to waddch is blank, and it uses the special color pair 0,
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
These limits apply to color values and color pairs.
Values outside these limits are not legal, and may result in a runtime error:
.IP • 4 COLORS corresponds to the terminal database's max_colors capability, (see terminfo(5)).
.IP • 4 color values are expected to be in the range 0 to COLORS-1, inclusive (including 0 and COLORS-1).
.IP • 4 a special color value -1 is used in certain extended functions to denote the default color (see use_default_colors(3X)).
.IP • 4 COLOR_PAIRS corresponds to the terminal database's max_pairs capability, (see terminfo(5)).
.IP • 4 legal color pair values are in the range 1 to COLOR_PAIRS-1, inclusive.
.IP • 4 color pair 0 is special; it denotes ``no color''.
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 attribute.
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 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:
.IP • 4 The first argument must be a legal color pair value. If default colors are used (see use_default_colors(3X)) the upper limit is adjusted to allow for extra pairs which use a default color in foreground and/or background.
.IP • 4 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(3X) routine, or to specify the use of default colors (color number -1) if you first invoke the use_default_colors(3X) routine.
Because init_pair uses signed shorts for its parameters, that limits color-pairs and color-values to 32767 on modern hardware. The extension init_extended_pair uses ints for the color-pair and color-value, allowing a larger number of colors to be supported.
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).
.IP • 4 The first argument must be a legal color value; default colors are not allowed here. (See the section Colors for the default color index.)
.IP • 4 Each of the last three arguments must be a value in the range 0 through 1000.
Because init_color uses signed shorts for its parameters, that limits color-values and their red, green, and blue components to 32767 on modern hardware. The extension init_extended_color uses ints for the color value and for setting the red, green, and blue components, allowing a larger number of colors to be supported.
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
.IP • 4 The first argument must be a legal color value, i.e., 0 through COLORS-1, inclusive.
.IP • 4 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.
Because color_content uses signed shorts for its parameters, that limits 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.
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.
.IP • 4 The first argument must be a legal color value, i.e., in the range 1 through COLOR_PAIRS-1, inclusive.
.IP • 4 The values that are stored at the addresses pointed to by the second and third arguments are in the range 0 through COLORS, inclusive.
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 colors to be supported.
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.
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.
SVr4 does document some error conditions which apply in general:
.IP • 4 This implementation will return ERR 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.
Specific functions make additional checks:
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:
.IP • 4 COLOR_YELLOW is actually brown. To get yellow, use COLOR_YELLOW combined with the A_BOLD attribute.
.IP • 4 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).
.IP • 4 Color RGB values are not settable.
The init_pair routine accepts negative values of foreground and background 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) 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.
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.