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   can_change_color.3x    ( 3 )

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Описание (Description)

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.