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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | PORTABILITY | SEE ALSO | COLOPHON |
curs_bkgd(3X) curs_bkgd(3X)
bkgdset, wbkgdset, bkgd, wbkgd, getbkgd - curses window background
manipulation routines
#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);
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.
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.
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.
These functions are described in the XSI Curses standard, Issue 4
(X/Open Curses).
curses(3X), curs_addch(3X), curs_attr(3X), curs_outopts(3X)
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⟨git://ncurses.scripts.mit.edu/ncurses.git⟩ on 2020-08-13. (At that
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curs_bkgd(3X)