- 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.
+ The background character is a special case: it includes a character
+ code, 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:
+ 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
+ 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 attri-
- bute next, and finally 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
+ 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
+ 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
+ COLOR_BLACK
+ COLOR_RED
+ COLOR_GREEN
+ COLOR_YELLOW
+ COLOR_BLUE
+ COLOR_MAGENTA
+ COLOR_CYAN
+ COLOR_WHITE
- Some terminals support more than the eight (8) "ANSI" colors. There
+ Some terminals support more than the eight (8) "ANSI" colors. There
are no standard names for those additional colors.
- 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.
+ is initialized by start_color to the maximum number of color pairs the
+ 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,
+ 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
+ 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
+ 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
+ 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.
+ 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
+ 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 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(3X)).
+ 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".
+ 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 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.
+ 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(3X)) the upper limit is ad-
- justed to allow for extra pairs which use a default color in fore-
- ground 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.
- Because init_pair uses signed shorts for its parameters, that limits
- color-pairs and color-values to 32767 on modern hardware. The exten-
- sion init_extended_pair uses ints for the color-pair and color-value,
- allowing a larger number of colors to be supported.
+ 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
- through 1000.
+ 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 mod-
- ern hardware. The extension init_extended_color uses ints for the col-
- or value and for setting the red, green, and blue components, allowing
- a larger number of colors to be supported.
+ 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
+ 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.
+ 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
- COLORS-1, inclusive.
+ 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 lim-
- its color-values and their red, green, and blue components to 32767 on
- modern hardware. The extension extended_color_content uses ints for
+ 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 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
- 1 through COLOR_PAIRS-1, inclusive.
+ 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 col-
- ors to be supported.
+ 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 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.
-
+ 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.
-
- 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.
+
+ 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.
+ 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 con-
- ditions which apply in general:
+ 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 ex-
- tension), or use color pairs outside the range 0 to COLOR_PAIRS-1.
+ 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.
+ 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 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_con-
- tent if the pair was not initialized using init_pairs and it re-
- turns ERR from color_content if the terminal does not support
+ 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.
+ This implementation does not return ERR for either case.
Specific functions make additional checks:
- init_color
+ init_color
returns an error if the terminal does not support this feature,
- e.g., if the initialize_color capability is absent from the
+ e.g., if the initialize_color capability is absent from the
terminal description.
- start_color
+ start_color
returns an error if the color table cannot be allocated.
- 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.
To change the background color used when parts of a window are blanked
- by erasing or scrolling operations, see curs_bkgd(3X).
+ by erasing or scrolling operations, see curs_bkgd(3x).
Several caveats apply on older x86 machines (e.g., i386, i486) with
VGA-compatible graphics:
- o COLOR_YELLOW is actually brown. To get yellow, use COLOR_YELLOW
- combined with the A_BOLD attribute.
+ o COLOR_YELLOW is actually brown. To get yellow, use COLOR_YELLOW
+ combined with the A_BOLD attribute.
- o The A_BLINK attribute should in theory cause the background to go
+ o 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).
- o Color RGB values are not settable.
+ 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.
+
+ This implementation satisfies X/Open Curses's minimum maximums for
+ COLORS and COLOR_PAIRS.
- 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.
+ 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.
+ 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 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
- color pairs which a terminal can support. However, in its use of short
- for the parameters, it carries over SVr4's implementation detail for
+ 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-
+ 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.