# curs_bkgrnd 3x 2023-12-23 ncurses 6.4 Library calls

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

## 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 6.4                       2023-12-23                   curs_bkgrnd(3x)