curs_bkgd(3) curs_bkgd(3)
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:
o The attribute part of the background is combined (OR'ed) with all
non-blank characters that are written into the window with waddch.
o 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:
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 colors
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.
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.
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 character.
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
background.
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 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
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(3)
ncurses 6.4 - Generated Tue Jan 3 15:38:47 CST 2023