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curs_bkgrnd 3x 2024-03-23 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                       2024-03-23                   curs_bkgrnd(3x)