- 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.
+ curses supports color attributes on terminals with that capability.
+ Call start_color (typically right after initscr(3x)) to enable this
+ feature. Colors are always used in pairs. A colorpair couples a
+ foreground color for characters with a background color for the blank
+ field on which characters are rendered. init_pair initializes a color
+ pair. The macro COLOR_PAIR(n) can then 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.
+ If a terminal has the relevant capability, init_color permits
+ (re)definition of a color. has_colors and can_change_color return TRUE
+ or FALSE, depending on whether the terminal has color capability and
+ whether the programmer can change the colors. color_content permits
+ extraction of the red, green, and blue components of an initialized
+ color. pair_content permits discovery of a color pair's current
+ definition.
-
+ curses combines the following data to render a character cell. Any of
+ them can include color information.
- o per-character video attributes (e.g., via waddch),
+ ocurses character attributes, as from waddch(3x) or wadd_wch(3x)
- o the window attribute (e.g., by wattrset), and
+ o window attributes, as from wattrset(3x) or wattr_set(3x)
- o the background character (e.g., wbkgdset).
+ o window background character attributes, as from wbkgdset(3x) or
+ wbkgrndset(3x)
- 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.
+ Per-character and window attributes are usually set through a function
+ parameter containing attributes including a color pair value. Some
+ functions, such as wattr_set, use a separate color pair number
+ parameter.
The background character is a special case: it includes a character
- value, just as if it were passed to waddch.
+ code, just as if it were passed to waddch.
- The curses library does the actual work of combining these color pairs
+ The curses library does the actual work of combining these color pairs
in an internal function called from waddch:
o If the parameter passed to waddch is blank, and it uses the special
color pair 0,
- ocurses next checks the window attribute.
+ ocurses next checks the window attribute.
- o If the window attribute does not use color pair 0, curses uses
+ o If the window attribute does not use color pair 0, curses uses
the color pair from the window attribute.
- o Otherwise, curses uses the background character.
+ o Otherwise, curses uses the background character.
o If the parameter passed to waddch is notblank, 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.
+ the special color pair 0, curses prefers the color pair from the
+ parameter, if it is nonzero. Otherwise, it tries the window
+ attribute 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.
+ Some curses functions such as wprintw call waddch. Those do not
+ combine its parameter with a color pair. Consequently those calls use
+ only the window attribute or the background character.
In <curses.h> the following macros are defined. These are the standard
- colors (ISO-6429). curses also assumes that COLOR_BLACK is the default
+ colors (ISO-6429). curses also assumes that COLOR_BLACK is the default
background color for all terminals.
COLOR_BLACK
@@ -162,188 +169,252 @@
- is initialized by start_color to the maximum number of colors the ter-
- minal can support.
+ is initialized by start_color to the maximum number of colors the
+ terminal can support.
is initialized by start_color to the maximum number of color pairs the
- terminal can support.
+ terminal can support. Often, its value is the product COLORS x COLORS,
+ but this is not always true.
+
+ o A few terminals use the HLS color space (see start_color below),
+ ignoring this rule; and
+
+ o terminals supporting a large number of colors are limited to the
+ number of color pairs that a signedshort value can represent.
- 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:
+ The start_color 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 initscr. start_color does this:
- o It initializes two global variables, COLORS and COLOR_PAIRS (re-
- spectively defining the maximum number of colors and color-pairs
+ o It initializes two global variables, COLORS and COLOR_PAIRS
+ (respectively defining the maximum number of colors and color pairs
the terminal can support).
- o It initializes the special color pair 0 to the default foreground
+ o It initializes the special color pair 0 to the default foreground
and background colors. No other color pairs are initialized.
- o It restores the colors on the terminal to the values they had when
+ o It restores the colors on the terminal to the values they had when
the terminal was just turned on.
- o 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.
+ o 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), and
- after that (if the terminal supports more than eight colors) the
- components are initialized to 1000.
+ 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.
+ match its built-in table. An application may use init_color to
+ alter 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:
+ These limits apply to color values and color pairs. Values outside
+ these limits are not valid, and may result in a runtime error:
- oCOLORS corresponds to the terminal database's max_colors capabili-
- ty, (see terminfo(5)).
+ oCOLORS corresponds to the terminal database's max_colors
+ capability, (see terminfo(5)).
- o color values are expected to be in the range 0 to COLORS-1, inclu-
- sive (including 0 and COLORS-1).
+ o color values are expected to be in the range 0 to COLORS-1,
+ inclusive (including 0 and COLORS-1).
- o a special color value -1 is used in certain extended functions to
- denote the defaultcolor (see use_default_colors).
+ o a special color value -1 is used in certain extended functions to
+ denote the defaultcolor (see use_default_colors(3x)).
- oCOLOR_PAIRS corresponds to the terminal database's max_pairs capa-
- bility, (see terminfo(5)).
+ oCOLOR_PAIRS corresponds to the terminal database's max_pairs
+ capability, (see terminfo(5)).
- o legal color pair values are in the range 1 to COLOR_PAIRS-1, inclu-
- sive.
+ o valid color pair values are in the range 1 to COLOR_PAIRS-1,
+ inclusive.
o 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.
+ 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.
- 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.
+ 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-indepen-
- dent programs.
+ 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 fore-
- ground color number, and the background color number. For portable ap-
- plications:
+ 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:
- o The first argument must be a legal color pair value. If default
- colors are used (see use_default_colors) the upper limit is adjust-
- ed to allow for extra pairs which use a default color in foreground
- and/or background.
+ o The first argument must be a valid 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.
- o The second and third arguments must be legal color values.
+ o The second and third arguments must be valid 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.
+ 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 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)
+ 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.
- 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.
+
+
+ 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
+ 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).
- o The first argument must be a legal color value; default colors are
- not allowed here. (See the section Colors for the default color
+ o The first argument must be a valid color value; default colors are
+ not allowed here. (See the section Colors for the default color
index.)
- o Each of the last three arguments must be a value in the range 0
+ o 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
+ When init_color is used, all occurrences of that color on the screen
immediately change to the new definition.
+
+ 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 com-
- ponents in the given color.
+ 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 given color.
- o The first argument must be a legal color value, i.e., 0 through
+ o The first argument must be a valid color value, i.e., 0 through
COLORS-1, inclusive.
- o The values that are stored at the addresses pointed to by the last
- three arguments are in the range 0 (no component) through 1000
+ o 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-
+ 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.
- o The first argument must be a legal color value, i.e., in the range
+ o The first argument must be a valid color value, i.e., in the range
1 through COLOR_PAIRS-1, inclusive.
- o 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.
+ o 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.
- 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.
+ 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.
+
+
+
+ PAIR_NUMBER(attr) extracts the color information from its attr
+ parameter and returns it as a color pair number; it is the inverse
+ operation of COLOR_PAIR.
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.
+ 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:
+
+ o 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.
+
+ Color values used in init_color must be in the range 0 to 1000.
- X/Open defines no error conditions. 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. 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.
+ 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.
+
+ o SVr4 does much the same, except that it returns ERR from
+ pair_content if the pair was not initialized using init_pairs and
+ it returns 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,
@@ -355,12 +426,12 @@
- 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.
+ In the ncurses implementation, there is a separate color activation
+ flag, color palette, color pairs table, and associated COLORS and
+ COLOR_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.
@@ -382,40 +453,93 @@
o Color RGB values are not settable.
+
+ The functions marked as extensions were designed for ncurses(3x), and
+ are not found in SVr4 curses, 4.4BSD curses, or any other previous
+ curses implementation.
+
+
- This implementation satisfies XSI Curses's minimum maximums for COLORS
- and COLOR_PAIRS.
+ Applications employing ncurses extensions should condition their use on
+ the visibility of the NCURSES_VERSION preprocessor macro.
- 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.
+ This implementation satisfies X/Open Curses's minimum maximums for
+ COLORS and COLOR_PAIRS.
+
+ 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) exten-
- sion.
+ 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 pa-
- rameters when null.
+ 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
+ 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
+ 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-
+ 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.
+ The reset_color_pairs function is an extension of ncurses.
+
+
+
+ SVr3.2 introduced color support to curses in 1987.
+
+ SVr4 made internal changes, e.g., moving the storage for the color
+ state from SP (the SCREEN structure) to cur_term (the TERMINAL
+ structure), but provided the same set of library functions.
+
+ 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 chtype
+ data type (denoted by A_COLOR).
+
+ Other implementations of curses had different limits:
+
+ o PCCurses (1987-1990) provided for only eight (8) colors.
+
+ o PDCurses (1992-present) inherited the 8-color limitation from
+ PCCurses, but changed this to 256 in version 2.5 (2001), along with
+ changing chtype from 16-bits to 32-bits.
+
+ o X/Open Curses (1992-present) added a new structure cchar_t to store
+ the character, attributes and color pair values, allowing increased
+ range of color pairs. Both color pairs and color-values used a
+ signed short, limiting values to 15 bits.
+
+ oncurses (1992-present) uses eight bits for A_COLOR in chtype
+ values.
+
+ Version 5.3 provided a wide-character interface (2002), but left
+ color pairs as part of the attributes-field.
+
+ Since version 6 (2015), ncurses uses a separate int for color pairs
+ in the cchar_t values. When those color pair values fit in 8 bits,
+ ncurses allows color pairs to be manipulated via the functions
+ using chtype values.
+
+ o 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 cchar_t, limiting the number of color pairs by
+ the size of the bitfield.