# curs_bkgd 3x 2024-04-20 ncurses 6.5 Library calls

    curs_bkgd(3x)                    Library calls                   curs_bkgd(3x)

## NAME

           bkgdset,  wbkgdset,  bkgd,  wbkgd, getbkgd - manipulate background of a
           curses window of characters

## SYNOPSIS

           #include <curses.h>

           int bkgd(chtype ch);
           int wbkgd(WINDOW *win, chtype ch);

           void bkgdset(chtype ch);
           void wbkgdset(WINDOW *win, chtype ch);

           chtype getbkgd(WINDOW *win);

## DESCRIPTION

           The  background  of  a  curses  window  (in  the  library's  non-"wide"
           configuration)   is  a  chtype  combining  a  set  of  attributes  (see
           curs_attr(3x)) with a 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 waddch(3x) and winsch(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.

### bkgd, wbkgd

           bkgd  and  wbkgd 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.

### bkgdset, wbkgdset

           bkgdset and  wbkgdset  manipulate  the  background  of  the  applicable
           window, without updating the character cells as bkgd and wbkgd do; only
           future writes reflect the updated background.

### getbkgd

           getbkgd obtains the given window's background character  and  attribute
           combination.

## RETURN VALUE

           Functions  returning  an int return OK on success.  bkgd returns ERR if
           the library has not been initialized.  wbkgd and getbkgd return ERR  if
           a WINDOW pointer argument is null.

           bkgdset and wbkgdset do not return a value.

           getbkgd   returns   a   window's  background  character  and  attribute
           combination.

## NOTES

           Unusually, there is no wgetbkgd function; getbkgd behaves as one  would
           expect wgetbkgd to, accepting a WINDOW pointer argument.

           bkgd and bkgdset may be implemented as macros.

           X/Open  Curses  mentions that the character part of the background must
           be a single-byte value.  ncurses, like SVr4 curses,  checks  to  ensure
           that, and will reuse the old background character if the check fails.

## PORTABILITY

           X/Open  Curses,  Issue  4 describes these functions.  It specifies that
           bkgd, wbkgd, and getbkgd return ERR on failure  (in  the  case  of  the
           last,  this  value  is  cast  to  chtype),  but  describes  no  failure
           conditions.

           The SVr4.0 manual says that bkgd and wbkgd may return  OK  "or  a  non-
           negative  integer  if immedok is set", which refers to the return value
           from wrefresh(3x), used to implement the  immediate  repainting.   SVr4
           curses's  wrefresh  returns  the  number  of  characters written to the
           screen during the refresh.  ncurses does not do that.

           Neither X/Open  Curses  nor  the  SVr4  manual  pages  detail  how  the
           rendition  of  characters  on  the  screen  updates  when bkgd or wbkgd
           changes the background character.  ncurses, like SVr4 curses, does  not
           (in  its  non-"wide"  configuration)  store  the  background and window
           attribute contributions to each character cell separately.

## SEE ALSO

           curs_bkgrnd(3x) describes the corresponding  functions  in  the  "wide"
           configuration of ncurses.

           curses(3x), curs_addch(3x), curs_attr(3x)

    ncurses 6.5                       2024-04-20                     curs_bkgd(3x)