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curs_bkgrnd(3)                  Library calls                 curs_bkgrnd(3)


NAME

       bkgrnd, wbkgrnd, bkgrndset, wbkgrndset, getbkgrnd, wgetbkgrnd -
       manipulate background of a curses window of wide characters


SYNOPSIS

       #include <curses.h>

       int bkgrnd(const cchar_t *wch);
       int wbkgrnd(WINDOW *win, const cchar_t *wch);

       void bkgrndset(const cchar_t *wch);
       void wbkgrndset(WINDOW *win, const cchar_t *wch);

       int getbkgrnd(cchar_t *wch);
       int wgetbkgrnd(WINDOW *win, cchar_t *wch);


DESCRIPTION

       The background of a curses window (in the library's "wide"
       configuration) is a cchar_t combining a set of attributes (see
       curs_attr(3X)) with a complex character called the blank character.

       The blank character is a spacing character that populates a window's
       character cells when their contents are erased without replacement.
       The background's attributes are combined with all non-blank characters
       written to the window, as with the wadd_wch(3X) and wins_wch(3X)
       families of functions.

       The blank character and attributes of the background combine with
       characters written to the window as described below.  The background
       becomes a property of the character and moves with it through any
       scrolling and insert/delete line/character operations.

       To the extent possible on a given terminal, the attribute part of the
       background is displayed as the graphic rendition of the character put
       on the screen.

   bkgrnd, wbkgrnd
       bkgrnd and wbkgrnd set the background property of stdscr or the
       specified window and then apply this setting to every character cell in
       that window.

       o   The rendition of every character in the window changes to the new
           background rendition.

       o   Wherever the former background character appears, it changes to the
           new background character.

       ncurses updates the rendition of each character cell by comparing the
       character, non-color attributes, and colors.  The library applies to
       following procedure to each cell in the window, whether or not it is
       blank.

       o   ncurses first compares the cell's character to the previously
           specified blank character; if they match, ncurses writes the new
           blank character to the cell.

       o   ncurses then checks if the cell uses color, that is, its color pair
           value is nonzero.  If not, it simply replaces the attributes and
           color pair in the cell with those from the new background
           character.

       o   If the cell uses color, and its background color matches that of
           the current window background, ncurses removes attributes that may
           have come from the current background and adds those from the new
           background.  It finishes by setting the cell's background to use
           the new window background color.

       o   If the cell uses color, and its background color does not match
           that of the current window background, ncurses updates only the
           non-color attributes, first removing those that may have come from
           the current background, and then adding attributes from the new
           background.

       ncurses treats a background character value of zero (0) as a blank
       character.

       If the terminal does not support color, or if color has not been
       initialized with start_color(3X), ncurses ignores the new background
       character's color attribute.

   bkgrndset, wbkgrndset
       bkgrndset and wbkgrndset manipulate the background of the applicable
       window, without updating the character cells as bkgrnd and wbkgrnd do;
       only future writes reflect the updated background.

   getbkgrnd, wgetbkgrnd
       The getbkgrnd and wgetbkgrnd functions obtain the background character
       and attribute pair of stdscr or the specified window and store it via
       the wch pointer.


RETURN VALUE

       bkgrndset and wbkgrndset do not return a value.

       The other functions return ERR upon failure and OK upon success.  In
       ncurses, failure occurs if

       o   a WINDOW pointer win is null, or

       o   a cchar_t pointer wch is null.


NOTES

       bkgrnd, bkgrndset, and getbkgrnd may be implemented as macros.

       Unlike their counterparts in the non-"wide" configuration of ncurses,
       getbkgrnd and wgetbkgrnd supply the background character and attribute
       in a modifiable cchar_t parameter, not as the return value.


PORTABILITY

       X/Open Curses, Issue 4 describes these functions.  It specifies no
       error conditions for them.

       X/Open Curses does not provide details of how the rendition is updated.
       This implementation follows the approach used in SVr4 curses.


SEE ALSO

       curs_bkgd(3X) describes the corresponding functions in the non-"wide"
       configuration of ncurses.

       curses(3X), curs_add_wch(3X), curs_attr(3X)

ncurses 6.5                       2024-04-20                   curs_bkgrnd(3)

ncurses 6.5 - Generated Sat May 4 09:01:25 CDT 2024
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