curs_bkgd(3x) — Linux manual page


curs_bkgd(3X)                                              curs_bkgd(3X)

NAME         top

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

SYNOPSIS         top

       #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         top

       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

       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 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

       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.

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

RETURN VALUE         top

       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         top

       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         top

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

SEE ALSO         top

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

COLOPHON         top

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