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:

       • 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
       curses(3X), curs_addch(3X), curs_attr(3X), curs_outopts(3X)

                                                                 curs_bkgd(3X)