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

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 set the background for a window. A window's 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 blank
characters that are written into the window.

The background becomes a property of each 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.

When bkgdset is used to set the background character, that does not update each cell
in the window. A subsequent call to bkgd will only modify the character in cells
which match the current 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 (0), 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