start_color - Cheap VPS LLC

curs_color


Section: Miscellaneous Library Functions (3X)
Updated:
Index
Return to Main Contents

 

NAME

start_color,
init_pair,
init_color,
has_colors,
can_change_color,
color_content,
pair_content,
COLOR_PAIRcurses color manipulation routines

 

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

 

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.

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 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
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 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_PAIR-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 curs_bkgd(3X).

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.

The init_pair routine accepts negative values of foreground
and background color to support the use_default_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
assume_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.
 

SEE ALSO

curses(3X),
curs_initscr(3X),
curs_attr(3X),
default_colors(3X)



 

Index



NAME

SYNOPSIS

DESCRIPTION


Overview

Routine Descriptions

Colors


RETURN VALUE

NOTES

PORTABILITY

SEE ALSO



Back to Top

PayPal Logo┬ęCheap VPS LLC - Leader of affordable VPS Hosting Services