+ 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
@@ -91,18 +94,89 @@
The routine pair_content allows a programmer to find out
how a given color-pair is currently defined.
- RoutineDescriptions
+
+
+ The curses library combines these inputs to produce the
+ actual foreground and background colors shown on the
+ screen:
+
+ o per-character video attributes (e.g., via waddch),
+
+ o the window attribute (e.g., by wattrset), and
+
+ o the background character (e.g., wbkgdset).
+
+ 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.
+
+ 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:
+
+ o If the parameter passed to waddch is blank, and it us-
+ es the special color pair 0,
+
+ 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.
+
+ 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 attribute next, and fi-
+ nally the background character.
+
+ 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 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.
+ 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
@@ -200,10 +274,13 @@
to by the second and third arguments are in the range 0
through COLORS, inclusive.
- 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.
+ the standard colors (ISO-6429). curses also assumes that
+ COLOR_BLACK is the default background color for all termi-
+ nals.
COLOR_BLACKCOLOR_RED
@@ -216,87 +293,87 @@
-
RETURN VALUE
- The routines can_change_color() and has_colors() return
+
+ 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
+ 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
+ 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
+ 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-
+ 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-
+ returns an error if the color table cannot be al-
located.
-
NOTES
- In the ncurses implementation, there is a separate color
+
+ 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.
+ 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
+ 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
+ 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-
+ Several caveats apply on 386 and 486 machines with VGA-
compatible graphics:
- o COLOR_YELLOW is actually brown. To get yellow, use
+ 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
+ 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
+ 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.
-
PORTABILITY
- This implementation satisfies XSI Curses's minimum maxi-
+
+ 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
+ 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-
+ 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
+ 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.