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color(3NCURSES) | color(3NCURSES) |
NAME¶
start_color, init_pair, init_color, has_colors, can_change_color, color_content, pair_content, COLOR_PAIR - curses color manipulation routinesSYNOPSIS¶
# include <curses.h>DESCRIPTION¶
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 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 displayed). A programmer initializes a color-pair with the routine init_pair. After it has been initialized, 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 programmer can use the routine init_color to change the definition 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.Routine Descriptions¶
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, except that 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 background.
- •
- The value of the second and third arguments must be between 0 and COLORS. 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.
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
RETURN VALUE¶
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 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.- init_color
- returns an error if the terminal does not support this feature, e.g., if the initialize_color capability is absent from the terminal description.
- start_color
- returns an error if the color table cannot be allocated.
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. 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 bkgd(3NCURSES). Several caveats apply on 386 and 486 machines with VGA-compatible graphics:- •
- COLOR_YELLOW is actually brown. To get yellow, use COLOR_YELLOW combined with the A_BOLD attribute.
- •
- 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).
- •
- Color RGB values are not settable.