1curs_color(3X) curs_color(3X)
2
6 start_color, has_colors, can_change_color, init_pair, init_color,
7 color_content, pair_content, reset_color_pairs, COLOR_PAIR, PAIR_NUMBER
8 - curses color manipulation routines
9
11 #include <curses.h>
12 int start_color(void);
14 bool has_colors(void);
16 bool can_change_color(void);
17 int init_pair(short pair, short f, short b);
19 int init_color(short color, short r, short g, short b);
20 /* extensions */
21 int init_extended_pair(int pair, int f, int b);
22 int init_extended_color(int color, int r, int g, int b);
23 int color_content(short color, short *r, short *g, short *b);
25 int pair_content(short pair, short *f, short *b);
26 /* extensions */
27 int extended_color_content(int color, int *r, int *g, int *b);
28 int extended_pair_content(int pair, int *f, int *b);
29 /* extensions */
31 void reset_color_pairs(void);
32 int COLOR_PAIR(int n);
34 PAIR_NUMBER(attrs);
35
37 Overview
38 curses supports color attributes on terminals with that capability. To
39 use these routines start_color must be called, usually right after
40 initscr. Colors are always used in pairs (referred to as color-pairs).
41 A color-pair consists of a foreground color (for characters) and a
42 background color (for the blank field on which the characters are dis‐
43 played). A programmer initializes a color-pair with the routine
44 init_pair. After it has been initialized, COLOR_PAIR(n) can be used to
45 convert the pair to a video attribute.
46 If a terminal is capable of redefining colors, the programmer can use
48 the routine init_color to change the definition of a color. The rou‐
49 tines has_colors and can_change_color return TRUE or FALSE, depending
50 on whether the terminal has color capabilities and whether the program‐
51 mer can change the colors. The routine color_content allows a program‐
52 mer to extract the amounts of red, green, and blue components in an
53 initialized color. The routine pair_content allows a programmer to
54 find out how a given color-pair is currently defined.
55 Color Rendering
57 The curses library combines these inputs to produce the actual fore‐
58 ground and background colors shown on the screen:
59 · per-character video attributes (e.g., via waddch),
61 · the window attribute (e.g., by wattrset), and
63 · the background character (e.g., wbkgdset).
65 Per-character and window attributes are usually set by a parameter con‐
67 taining video attributes including a color pair value. Some functions
68 such as wattr_set use a separate parameter which is the color pair num‐
69 ber.
70 The background character is a special case: it includes a character
72 value, just as if it were passed to waddch.
73 The curses library does the actual work of combining these color pairs
75 in an internal function called from waddch:
76 · If the parameter passed to waddch is blank, and it uses the special
78 color pair 0,
79 · curses next checks the window attribute.
81 · If the window attribute does not use color pair 0, curses uses
83 the color pair from the window attribute.
84 · Otherwise, curses uses the background character.
86 · If the parameter passed to waddch is not blank, or it does not use
88 the special color pair 0, curses prefers the color pair from the
89 parameter, if it is nonzero. Otherwise, it tries the window at‐
90 tribute next, and finally the background character.
91 Some curses functions such as wprintw call waddch. Those do not com‐
93 bine its parameter with a color pair. Consequently those calls use on‐
94 ly the window attribute or the background character.
95
97 In <curses.h> the following macros are defined. These are the standard
98 colors (ISO-6429). curses also assumes that COLOR_BLACK is the default
99 background color for all terminals.
100 COLOR_BLACK
102 COLOR_RED
103 COLOR_GREEN
104 COLOR_YELLOW
105 COLOR_BLUE
106 COLOR_MAGENTA
107 COLOR_CYAN
108 COLOR_WHITE
109 Some terminals support more than the eight (8) “ANSI” colors. There
111 are no standard names for those additional colors.
112
114 COLORS
115 is initialized by start_color to the maximum number of colors the ter‐
116 minal can support.
117 COLOR_PAIRS
119 is initialized by start_color to the maximum number of color pairs the
120 terminal can support.
121
123 start_color
124 The start_color routine requires no arguments. It must be called if
125 the programmer wants to use colors, and before any other color manipu‐
126 lation routine is called. It is good practice to call this routine
127 right after initscr. start_color does this:
128 · It initializes two global variables, COLORS and COLOR_PAIRS (re‐
130 spectively defining the maximum number of colors and color-pairs
131 the terminal can support).
132 · It initializes the special color pair 0 to the default foreground
134 and background colors. No other color pairs are initialized.
135 · It restores the colors on the terminal to the values they had when
137 the terminal was just turned on.
138 · If the terminal supports the initc (initialize_color) capability,
140 start_color initializes its internal table representing the red,
141 green and blue components of the color palette.
142 The components depend on whether the terminal uses CGA (aka “ANSI”)
144 or HLS (i.e., the hls (hue_lightness_saturation) capability is
145 set). The table is initialized first for eight basic colors
146 (black, red, green, yellow, blue, magenta, cyan, and white), and
147 after that (if the terminal supports more than eight colors) the
148 components are initialized to 1000.
149 start_color does not attempt to set the terminal's color palette to
151 match its built-in table. An application may use init_color to al‐
152 ter the internal table along with the terminal's color.
153 These limits apply to color values and color pairs. Values outside
155 these limits are not legal, and may result in a runtime error:
156 · COLORS corresponds to the terminal database's max_colors capabili‐
158 ty, (see terminfo(5)).
159 · color values are expected to be in the range 0 to COLORS-1, inclu‐
161 sive (including 0 and COLORS-1).
162 · a special color value -1 is used in certain extended functions to
164 denote the default color (see use_default_colors).
165 · COLOR_PAIRS corresponds to the terminal database's max_pairs capa‐
167 bility, (see terminfo(5)).
168 · legal color pair values are in the range 1 to COLOR_PAIRS-1, inclu‐
170 sive.
171 · color pair 0 is special; it denotes “no color”.
173 Color pair 0 is assumed to be white on black, but is actually what‐
175 ever the terminal implements before color is initialized. It can‐
176 not be modified by the application.
177 has_colors
179 The has_colors routine requires no arguments. It returns TRUE if the
180 terminal can manipulate colors; otherwise, it returns FALSE. This rou‐
181 tine facilitates writing terminal-independent programs. For example, a
182 programmer can use it to decide whether to use color or some other
183 video attribute.
184 can_change_color
186 The can_change_color routine requires no arguments. It returns TRUE if
187 the terminal supports colors and can change their definitions; other,
188 it returns FALSE. This routine facilitates writing terminal-indepen‐
189 dent programs.
190 init_pair
192 The init_pair routine changes the definition of a color-pair. It takes
193 three arguments: the number of the color-pair to be changed, the fore‐
194 ground color number, and the background color number. For portable ap‐
195 plications:
196 · The first argument must be a legal color pair value. If default
198 colors are used (see use_default_colors) the upper limit is adjust‐
199 ed to allow for extra pairs which use a default color in foreground
200 and/or background.
201 · The second and third arguments must be legal color values.
203 If the color-pair was previously initialized, the screen is refreshed
205 and all occurrences of that color-pair are changed to the new defini‐
206 tion.
207 As an extension, ncurses allows you to set color pair 0 via the as‐
209 sume_default_colors(3X) routine, or to specify the use of default col‐
210 ors (color number -1) if you first invoke the use_default_colors(3X)
211 routine.
212 The extension reset_color_pairs tells ncurses to discard all of the
214 color-pair information which was set with init_pair. It also touches
215 the current- and standard-screens, allowing an application to switch
216 color palettes rapidly.
217 init_color
219 The init_color routine changes the definition of a color. It takes
220 four arguments: the number of the color to be changed followed by three
221 RGB values (for the amounts of red, green, and blue components).
222 · The first argument must be a legal color value; default colors are
224 not allowed here. (See the section Colors for the default color
225 index.)
226 · Each of the last three arguments must be a value in the range 0
228 through 1000.
229 When init_color is used, all occurrences of that color on the screen
231 immediately change to the new definition.
232 color_content
234 The color_content routine gives programmers a way to find the intensity
235 of the red, green, and blue (RGB) components in a color. It requires
236 four arguments: the color number, and three addresses of shorts for
237 storing the information about the amounts of red, green, and blue com‐
238 ponents in the given color.
239 · The first argument must be a legal color value, i.e., 0 through
241 COLORS-1, inclusive.
242 · The values that are stored at the addresses pointed to by the last
244 three arguments are in the range 0 (no component) through 1000
245 (maximum amount of component), inclusive.
246 pair_content
248 The pair_content routine allows programmers to find out what colors a
249 given color-pair consists of. It requires three arguments: the color-
250 pair number, and two addresses of shorts for storing the foreground and
251 the background color numbers.
252 · The first argument must be a legal color value, i.e., in the range
254 1 through COLOR_PAIRS-1, inclusive.
255 · The values that are stored at the addresses pointed to by the sec‐
257 ond and third arguments are in the range 0 through COLORS, inclu‐
258 sive.
259 PAIR_NUMBER
261 PAIR_NUMBER(attrs) extracts the color value from its attrs parameter
262 and returns it as a color pair number.
263 COLOR_PAIR
265 Its inverse COLOR_PAIR(n) converts a color pair number to an attribute.
266 Attributes can hold color pairs in the range 0 to 255. If you need a
267 color pair larger than that, you must use functions such as attr_set
268 (which pass the color pair as a separate parameter) rather than the
269 legacy functions such as attrset.
270
272 The routines can_change_color and has_colors return TRUE or FALSE.
273 All other routines return the integer ERR upon failure and an OK (SVr4
275 specifies only “an integer value other than ERR”) upon successful com‐
276 pletion.
277 X/Open defines no error conditions. This implementation will return
279 ERR on attempts to use color values outside the range 0 to COLORS-1
280 (except for the default colors extension), or use color pairs outside
281 the range 0 to COLOR_PAIRS-1. Color values used in init_color must be
282 in the range 0 to 1000. An error is returned from all functions if the
283 terminal has not been initialized. An error is returned from secondary
284 functions such as init_pair if start_color was not called.
285 init_color
287 returns an error if the terminal does not support this feature,
288 e.g., if the initialize_color capability is absent from the
289 terminal description.
290 start_color
292 returns an error if the color table cannot be allocated.
293
295 In the ncurses implementation, there is a separate color activation
296 flag, color palette, color pairs table, and associated COLORS and COL‐
297 OR_PAIRS counts for each screen; the start_color function only affects
298 the current screen. The SVr4/XSI interface is not really designed with
299 this in mind, and historical implementations may use a single shared
300 color palette.
301 Setting an implicit background color via a color pair affects only
303 character cells that a character write operation explicitly touches.
304 To change the background color used when parts of a window are blanked
305 by erasing or scrolling operations, see curs_bkgd(3X).
306 Several caveats apply on older x86 machines (e.g., i386, i486) with
308 VGA-compatible graphics:
309 · COLOR_YELLOW is actually brown. To get yellow, use COLOR_YELLOW
311 combined with the A_BOLD attribute.
312 · The A_BLINK attribute should in theory cause the background to go
314 bright. This often fails to work, and even some cards for which it
315 mostly works (such as the Paradise and compatibles) do the wrong
316 thing when you try to set a bright “yellow” background (you get a
317 blinking yellow foreground instead).
318 · Color RGB values are not settable.
320
322 This implementation satisfies XSI Curses's minimum maximums for COLORS
323 and COLOR_PAIRS.
324 The init_pair routine accepts negative values of foreground and back‐
326 ground color to support the use_default_colors(3X) extension, but only
327 if that routine has been first invoked.
328 The assumption that COLOR_BLACK is the default background color for all
330 terminals can be modified using the assume_default_colors(3X) exten‐
331 sion.
332 This implementation checks the pointers, e.g., for the values returned
334 by color_content and pair_content, and will treat those as optional pa‐
335 rameters when null.
336 X/Open Curses does not specify a limit for the number of colors and
338 color pairs which a terminal can support. However, in its use of short
339 for the parameters, it carries over SVr4's implementation detail for
340 the compiled terminfo database, which uses signed 16-bit numbers. This
341 implementation provides extended versions of those functions which use
342 short parameters, allowing applications to use larger color- and pair-
343 numbers.
344 The reset_color_pairs function is an extension of ncurses.
346
348 curses(3X), curs_initscr(3X), curs_attr(3X), curs_variables(3X), de‐
349 fault_colors(3X)
350 curs_color(3X)