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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 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
#t or #f, 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.
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 prepares the procedures 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 return value is unspecified.
Returns the maximum number of colors the terminal can support.
Returns the maximum number of color-pairs the terminal can support.
These variables contain the color number of the eight default colors.
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 the value returned by the colors procedure. 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.
It returns #f on failure and #t on success. Failure may
indicate that, for the current terminal, the colors cannot be modified.
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 fore-ground 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. Color pair 0 is assumed to be white on black, but is
actually whatever the terminal implements before color is initialized.
If the color-pair was previously initialized, the screen is refreshed and all occurrences of that color-pair are changed to the new definition.
Color pair 0 is set via the assume-default-colors routine.
After use-default-colors has been called, the special color
number -1 can be used as fore-color or
back-color. Color number -1 is set to contain the default
foreground or background color for this screen, which is usually white
on black.
It returns #f on failure and #t on success. Failure may
indicate an attempt to change a color pair beyond the allow range of
color pairs.
The has-colors? routine returns #t if the terminal can
manipulate colors; otherwise, it returns #f. 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 returns #t if the terminal
supports colors and can change their definitions; otherwise, it
returns #f.
The color-content routine returns the intensity of the red,
green, and blue (RGB) components in a color. Given color as its
argument, it returns a list of three integers indicating the red,
green, and blue components in the given color. The value of the
color argument must be between 0 and the value returned by the
colors procedure. The values returned are between 0 (no
component) and 1000 (maximum amount of component).
The pair-content routine allows programmers to find out what
colors color-pair pair consists of. The value of pair
must be between 1 and color-pairs - 1. It returns a list of
two elements: the foreground color number and the background color
number. The values are between 0 and the value returned by
colors.
This procedure allow routines that use color numbers, like
init-pair! to use the special color number -1 to indicate the
default color. When -1 is used in lieu of the foreground color, it
indicated the default foreground color. When -1 is used as the
background color, it indicated the default background color. Thus, it
has different meanings depending on the context.
It returns #t if successful or #f is the terminal lacks
the capability to set color pair 0.
This procedure allow the modification of special color pair 0, which
cannot be modified by init-pair!. Color pair 0 is the default
foreground and background color for the window.
It returns #t if successful or #f is the terminal lacks
the capability to set color pair 0.
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