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bkgrnd(3x)

curs_bkgrnd(3x)                  Library calls                 curs_bkgrnd(3x)

NAME
       bkgrnd, wbkgrnd, bkgrndset, wbkgrndset, getbkgrnd, wgetbkgrnd - manipu‐
       late background of a curses window of wide characters

SYNOPSIS
       #include <ncursesw/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
       Every  curses  window  has  a background character property: in the li‐
       brary's wide configuration, it is a curses complex character  (cchar_t)
       that  combines a set of attributes (and, if colors are enabled, a color
       pair identifier) with a character code.  When erasing (parts of) a win‐
       dow, curses replaces the erased cells with the background character.

       curses also uses the background character when writing characters to  a
       populated window.

       •   The  attribute  part  of the background character combines with all
           non-blank character cells  in  the  window,  as  populated  by  the
           wadd_wch(3X) and wins_wch(3X) families of functions (and those that
           call them).

       •   Both  the character code and attributes of the background character
           combine with blank character cells in the window.

       The background character's set of attributes becomes a property of  the
       character cell and move with it through any scrolling and insert/delete
       line/character  operations.   To  the  extent  possible on the terminal
       type, curses displays the attributes of the background character as the
       graphic rendition of a character cell on the display.

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

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

       •   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 color pair selection.  The library
       applies  to  following procedure to each cell in the window, whether or
       not it is blank.

       •   ncurses first compares the cell's character to the previously spec‐
           ified background character; if they match, ncurses writes  the  new
           background character to the cell.

       •   ncurses then checks whether 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 char‐
           acter.

       •   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.

       •   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.

       If the new background's character is non-spacing,  ncurses  reuses  the
       old background character, except for one special case: ncurses treats a
       background character code of zero (0) as a space.

       If  the  terminal does not support color, or if color has not been ini‐
       tialized with start_color(3X), ncurses ignores the new background char‐
       acter's color pair selection.

   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
       getbkgrnd and wgetbkgrnd respectively obtain stdscr's or the given win‐
       dow's background character, attributes, and color pair, and store it in
       their wch argument.

RETURN VALUE
       bkgrndset and wbkgrndset do not return a value.

       Functions returning an int return ERR upon failure and OK upon success.
       In ncurses, failure occurs if

       •   the curses screen has not been initialized,

       •   win is NULL, or

       •   wch is NULL.


ATTRIBUTES
       See attributes(7) for descriptions of the following attributes:

       box; cbp-1 | cbp-1 l | l .  ATTRIBUTE TYPE ATTRIBUTE VALUE = Availabil‐
       ity   library/ncurses = Stability Uncommitted

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

       Unlike their counterparts in the  non-wide  configuration  of  ncurses,
       getbkgrnd and wgetbkgrnd store the background character in a modifiable
       cchar_t parameter, rather than supplying it as the return value.

       Source  code  for open source software components in Oracle Solaris can
       be found at https://www.oracle.com/downloads/opensource/solaris-source-
       code-downloads.html.

       This software was built from source available at:
       https://github.com/oracle/solaris-userland

       The original community source was downloaded from:
       https://invisible-mirror.net/archives/ncurses/cur‐
       rent/ncurses-6.5-20250614.tgz

       Further information about this software can be found on the open source
       community website at https://invisible-island.net/ncurses/.

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.
       ncurses follows the approach used in SVr4 curses's  non-wide  functions
       for manipulating the window background.

HISTORY
       X/Open Curses Issue 4 (1995) initially specified these functions.

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                       2025-02-15                   curs_bkgrnd(3x)
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