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)