Overview
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) can be used to convert the
pair to a 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.
Color Rendering
The curses library combines these inputs to produce the actual
foreground and background colors shown on the screen:
• per-character video attributes (e.g., via waddch),
• the window attribute (e.g., by wattrset), and
• the background character (e.g., wbkgdset).
Per-character and window attributes are usually set by a
parameter containing video attributes including a color 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:
• If the parameter passed to waddch is blank, and it uses the
special color pair 0,
• curses next checks the window attribute.
• If the window attribute does not use color pair 0, curses
uses the color pair from the window attribute.
• Otherwise, curses uses the background character.
• If the parameter passed to waddch is not blank, 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 finally the background
character.
Some curses functions such as wprintw call waddch. Those do not
combine its parameter with a color pair. Consequently those
calls use only the window attribute or the background character.
