can_change_color(), color_content(), has_colors(), init_color(), init_pair(), pair_content(), start_color()

curses color manipulation routines 

Curses Function


SYNOPSIS

#include <curses.h>

int start_color(void);

int init_pair(short pair, short f, short b);

int init_color(short color, short r, short g, short b);

bool has_colors(void);

bool can_change_color(void);

int color_content(short color, short *r, short *g, short *b);

int pair_content(short pair, short *f, short *b);


DESCRIPTION

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 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. 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.

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 component).

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 arguments 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

RETURN VALUES

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.


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 curs_bkgd().

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.


PORTABILITY

This implementation satisfies XSI Curses's minimum maximums for COLORS and COLOR_PAIRS.


AVAILABILITY

PTC MKS Toolkit for Professional Developers
PTC MKS Toolkit for Enterprise Developers
PTC MKS Toolkit for Enterprise Developers 64-Bit Edition


SEE ALSO

Functions:
curs_attr(), curs_initscr(), curses()


PTC MKS Toolkit 9.6 Documentation Build 9.