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:

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

       •   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:

       •   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.

       •   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.

       •   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.

       •   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

       ncurses(3NCURSES), addch(3NCURSES), attr(3NCURSES), outopts(3NCURSES)

                                                                                                  bkgd(3NCURSES)