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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | PORTABILITY | SEE ALSO | COLOPHON |
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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 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.
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)
This page is part of the ncurses (new curses) project.
Information about the project can be found at
⟨https://www.gnu.org/software/ncurses/ncurses.html⟩. If you have
a bug report for this manual page, send it to
bug-ncurses-request@gnu.org. This page was obtained from the
project's upstream Git mirror of the CVS repository
⟨https://github.com/mirror/ncurses.git⟩ on 2024-06-14. (At that
time, the date of the most recent commit that was found in the
repository was 2023-03-12.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
curs_bkgd(3X)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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