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 attr(3NCURSES)) 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(3NCURSES) and wins_wch(3NCURSES) 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.

       •   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  colors.  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  specified  blank  character;  if  they
           match, ncurses writes the new blank character to the cell.

       •   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.

       •   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.

       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(3NCURSES),
       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

       •   a WINDOW pointer win is null, or

       •   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

       bkgd(3NCURSES) describes the corresponding functions in the non-“wide” configuration of ncurses.

       ncurses(3NCURSES), add_wch(3NCURSES), attr(3NCURSES)

ncurses 6.4                                        2023-12-23                                   bkgrnd(3NCURSES)