- Overview
- curses support color attributes on terminals with that
- capability. To use these routines start_color must be
- called, usually right after initscr. Colors are always
+
+ 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 charac-
ters are displayed). A programmer initializes a color-
- pair with the routine init_pair. After it has been ini-
- tialized, COLOR_PAIR(n), a macro defined in <curses.h>,
+ pair with the routine init_pair. After it has been ini-
+ tialized, COLOR_PAIR(n), a macro defined in <curses.h>,
can be used as a new video attribute.
If a terminal is capable of redefining colors, the pro-
- grammer can use the routine init_color to change the defi-
- nition of a color. The routines has_colors and
- can_change_color return TRUE or FALSE, depending on
+ grammer can use the routine init_color to change the defi-
+ nition 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.
-
- RoutineDescriptions
- 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 initializes eight basic colors (black, red,
- green, yellow, blue, magenta, cyan, and white), and two
- global variables, COLORS and COLOR_PAIRS (respectively
- defining the maximum number of colors and color-pairs the
- terminal can support). It also restores the colors on the
- terminal to the values they had when the terminal was just
- turned on.
-
- 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:
-
- - The value of the first argument must be between 1 and
- COLOR_PAIRS-1.
-
- - The value of the second and third arguments must be
- between 0 and COLORS (the 0 color pair is wired to
- white on black and cannot be changed).
-
- If the color-pair was previously initialized, the screen
- is refreshed and all occurrences of that color-pair is
- changed to the new definition.
-
- As an extension, ncurses allows you to set color pair 0
- via the assume_default_colors routine, or to specify the
- use of default colors (color number -1) if you first
- invoke the use_default_colors routine.
-
- 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). The value of the first
- argument must be between 0 and COLORS. (See the section
- Colors for the default color index.) Each of the last
- three arguments must be a value between 0 and 1000. When
- init_color is used, all occurrences of that color on the
- screen immediately change to the new definition.
-
- 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 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 given color. The value of the first argument must be
- between 0 and COLORS. The values that are stored at the
- addresses pointed to by the last three arguments are
- between 0 (no component) and 1000 (maximum amount of com-
- ponent).
-
- 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. The value of the first argument must be
- between 1 and COLOR_PAIRS-1. The values that are stored
- at the addresses pointed to by the second and third argu-
- ments are between 0 and COLORS.
-
- Colors
- In <curses.h> the following macros are defined. These are
- the default colors. 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
+ the programmer can change the colors. The routine col-
+ or_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.
-
RETURN VALUE
- The routines can_change_color() and has_colors() return
- TRUE or FALSE.
+
+ The curses library combines these inputs to produce the
+ actual foreground and background colors shown on the
+ screen:
- All other routines return the integer ERR upon failure and
- an OK (SVr4 specifies only "an integer value other than
- ERR") upon successful completion.
+ o per-character video attributes (e.g., via waddch),
+ o the window attribute (e.g., by wattrset), and
-
-
NOTES
- 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.
+ o the background character (e.g., wbkgdset).
- 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 curs_bkgd(3x).
+ Per-character and window attributes are usually set by a
+ parameter containing video attributes including a COL-
+ OR_PAIR value. Some functions such as wattr_set use a
+ separate parameter which is the color pair number.
- Several caveats apply on 386 and 486 machines with VGA-
- compatible graphics:
+ The background character is a special case: it includes a
+ character value, just as if it were passed to waddch.
- - COLOR_YELLOW is actually brown. To get yellow, use
- COLOR_YELLOW combined with the A_BOLD attribute.
+ The curses library does the actual work of combining these
+ color pairs in an internal function called from waddch:
- - 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 If the parameter passed to waddch is blank, and it us-
+ es the special color pair 0,
- - Color RGB values are not settable.
+ ocurses next checks the window attribute.
+ o If the window attribute does not use color pair 0,
+ curses uses the color pair from the window at-
+ tribute.
-
-
PORTABILITY
- This implementation satisfies XSI Curses's minimum maxi-
- mums for COLORS and COLOR_PAIRS.
+ o Otherwise, curses uses the background character.
- The init_pair routine accepts negative values of fore-
- ground and background color to support the
- use_default_colors extension, but only if that routine has
- been first invoked.
+ 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 fi-
+ nally the background character.
- The assumption that COLOR_BLACK is the default background
- color for all terminals can be modified using the
- assume_default_colors extension,
+ Some curses functions such as wprintw call waddch. Those
+ do not combine its parameter with a color pair. Conse-
+ quently those calls use only the window attribute or the
+ background character.
+ 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 COL-
+ OR_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 and background colors. No other color
+ pairs are initialized.
+
+ 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.
+
+ The components depend on whether the terminal uses CGA
+ (aka "ANSI") or HLS (i.e., the hls (hue_lightness_sat-
+ uration) capability is set). The table is initialized
+ first for eight basic colors (black, red, green, yel-
+ low, blue, magenta, cyan, and white), and after that
+ (if the terminal supports more than eight colors) the
+ components are initialized to 1000.
+
+ start_color does not attempt to set the terminal's
+ color palette to match its built-in table. An appli-
+ cation may use init_color to alter the internal table
+ along with the terminal's color.
+
+ These limits apply to color values and color pairs. Val-
+ ues outside these limits are not legal, and may result in
+ a runtime error:
+
+ oCOLORS corresponds to the terminal database's max_col-
+ ors capability, which is typically a signed 16-bit in-
+ teger (see terminfo(5)).
+
+ o color values are expected to be in the range 0 to COL-
+ ORS-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_de-
+ fault_colors).
+
+ oCOLOR_PAIRS corresponds to the terminal database's
+ max_pairs capability, which is typically a signed
+ 16-bit integer (see terminfo(5)).
+
+ o legal color pair values are in the range 1 to COL-
+ OR_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 whatever the terminal implements before color
+ is initialized. It cannot be modified by the applica-
+ tion.
+
+ 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 adjusted to allow for extra pairs
+ which use a default color in foreground and/or back-
+ ground.
+ o 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 routine, or to specify the
+ use of default colors (color number -1) if you first in-
+ voke the use_default_colors routine.
+
+ 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). The first argument must
+ be a legal color value; default colors are not allowed
+ here. (See the section Colors for the default color in-
+ dex.) 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 immediately change
+ to the new definition.
+
+ 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 at-
+ tribute.
+ 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 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 given color. The first argument must be a legal color
+ value, i.e., 0 through COLORS-1, inclusive. 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.
+
+ 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. The first argument must be a legal color
+ value, i.e., in the range 1 through COLOR_PAIRS-1, inclu-
+ sive. The values that are stored at the addresses pointed
+ to by the second and third arguments are in the range 0
+ through COLORS, inclusive.
+
+ 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 termi-
+ nals.
+
+ COLOR_BLACK
+ COLOR_RED
+ COLOR_GREEN
+ COLOR_YELLOW
+ COLOR_BLUE
+ COLOR_MAGENTA
+ COLOR_CYAN
+ COLOR_WHITE
+
+ 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 completion.
+
+ 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 ex-
+ tension), or use color pairs outside the range 0 to COL-
+ OR_PAIRS-1. Color values used in init_color must be in
+ the range 0 to 1000. An error is returned from all func-
+ tions if the terminal has not been initialized. An error
+ is returned from secondary functions such as init_pair if
+ start_color was not called.
+
+ init_color
+ returns an error if the terminal does not support
+ this feature, e.g., if the initialize_color capa-
+ bility is absent from the terminal description.
+
+ start_color
+ returns an error if the color table cannot be al-
+ located.
+
+ In the ncurses implementation, there is a separate color
+ activation flag, color palette, color pairs table, and as-
+ sociated 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.
+ 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 curs_bkgd(3x).
+ Several caveats apply on 386 and 486 machines with VGA-
+ compatible graphics:
+ 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 back-
+ ground 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.
+
+ This implementation satisfies XSI Curses's minimum maxi-
+ mums for COLORS and COLOR_PAIRS.
+ The init_pair routine accepts negative values of fore-
+ ground and background color to support the use_de-
+ fault_colors 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 as-
+ sume_default_colors 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.
+