# curs_bkgd 3x

    curs_bkgd(3x)                                                    curs_bkgd(3x)

## NAME

           bkgdset,  wbkgdset,  bkgd,  wbkgd,  getbkgd  - curses window background
           manipulation routines

## SYNOPSIS

           #include <curses.h>

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

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

           chtype getbkgd(WINDOW *win);

## DESCRIPTION

### bkgdset

           The bkgdset and wbkgdset routines  manipulate  the  background  of  the
           named  window.   The  window  background  is a chtype consisting of any
           combination of attributes  (i.e.,  rendition)  and  a  character.   The
           attribute part of the background is combined (OR'ed) with all non-blank
           characters that are written into the  window  with  waddch.   Both  the
           character  and  attribute parts of the background are combined with the
           blank characters.  The background becomes a property of  the  character
           and  moves  with  the character through any scrolling and insert/delete
           line/character operations.

           To the extent possible on a particular terminal, the attribute part  of
           the  background  is displayed as the graphic rendition of the character
           put on the screen.

### bkgd

           The bkgd and wbkgd functions set the background property of the current
           or  specified  window  and  then  apply this setting to every character
           position in that window.  According to  X/Open  Curses,  it  should  do
           this:

           o   The  rendition  of  every character on the screen is changed to the
               new background rendition.

           o   Wherever the former background character appears, it is changed  to
               the new background character.

           Neither  X/Open Curses nor the SVr4 manual pages give details about the
           way the rendition of characters on the screen is updated when  bkgd  or
           wbkgd is used to change the background character.

           This  implementation,  like  SVr4 curses, does not store the background
           and window attribute contributions to each cell separately.  It updates
           the  rendition  by  comparing  the  character, non-color attributes and
           colors contained in the background.   For  each  cell  in  the  window,
           whether or not it is blank:

           o   The  library  first  compares  the character, and if it matches the
               current character part of the background, it replaces that with the
               new background character.

           o   The  library  then  checks  if the cell uses color, i.e., 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 that matches the color in  the  current
               background, the library removes attributes which may have come from
               the current background and adds attributes from the new background.
               It  finishes  by  setting  the  cell  to use the color from the new
               background.

           o   If the cell uses color, and that does not match the  color  in  the
               current   background,   the  library  updates  only  the  non-color
               attributes, first removing those  which  may  have  come  from  the
               current  background,  and  then  adding  attributes  from  the  new
               background.

           If the background's character value is zero, a space is assumed.

           If the terminal does not support  color,  or  if  color  has  not  been
           started   with   start_color,  the  new  background  character's  color
           attribute will be ignored.

### getbkgd

           The getbkgd function returns  the  given  window's  current  background
           character/attribute pair.

## RETURN VALUE

           These  functions are described in the XSI Curses standard, Issue 4.  It
           specifies that bkgd and wbkgd return  ERR  on  failure,  but  gives  no
           failure conditions.

           The  routines  bkgd and wbkgd return the integer OK, unless the library
           has not been initialized.

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

## NOTES

           Note that bkgdset and bkgd may be macros.

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

## PORTABILITY

           These  functions  are  described  in  the  XSI Curses standard, Issue 4
           (X/Open Curses).

## SEE ALSO

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

                                                                     curs_bkgd(3x)