curs_bkgd 3x

curs_bkgd(3x)                                                    curs_bkgd(3x)


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


       #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);



       The bkgdset and wbkgdset routines  manipulate  the  background  of  the
       named window.  The window background is a chtype consisting of any com-
       bination  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.


       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

       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 col-
       ors 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 char-

       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 back-

       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  cur-
           rent  background,  and  then  adding  attributes from the new back-


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


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


       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


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


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