https://invisible-island.net/ncurses/man/
curs_bkgrnd(3x) Library calls curs_bkgrnd(3x)
bkgrnd, wbkgrnd, bkgrndset, wbkgrndset, getbkgrnd, wgetbkgrnd -
manipulate background of a curses window of wide characters
#include <curses.h>
int bkgrnd(const cchar_t *wch);
int wbkgrnd(WINDOW *win, const cchar_t *wch);
void bkgrndset(const cchar_t *wch);
void wbkgrndset(WINDOW *win, const cchar_t *wch);
int getbkgrnd(cchar_t *wch);
int wgetbkgrnd(WINDOW *win, cchar_t *wch);
Every curses window has a background property. In the library's wide
configuration, this property is a cchar_t which combines a set of
attributes with the background character (see curs_attr(3x)) The
background character is a spacing character.
When erasing parts of the screen, curses fills the cells with the
background character. curses also uses the window background when
writing characters to the screen:
o The attribute part of the background is combined with all non-blank
characters that are written into the window, as with the
wadd_wch(3x) and wins_wch(3x) families of functions.
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 the character and moves with it
through any scrolling and insert/delete line/character operations.
To the extent possible on a given terminal, the attribute part of the
background is displayed as the graphic rendition of the character put
on the screen.
bkgrnd and wbkgrnd set the background property of stdscr or the
specified window and then apply this setting to every character cell in
that window.
o The rendition of every character in the window changes to the new
background rendition.
o Wherever the former background character appears, it changes to the
new background character.
ncurses updates the rendition of each character cell by comparing the
character, non-color attributes, and colors. The library applies to
following procedure to each cell in the window, whether or not it is
blank.
o ncurses first compares the cell's character to the previously
specified background character; if they match, ncurses writes the
new background character to the cell.
o ncurses then checks if the cell uses color, that is, 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 its background color matches that of
the current window background, ncurses removes attributes that may
have come from the current background and adds those from the new
background. It finishes by setting the cell's background to use
the new window background color.
o If the cell uses color, and its background color does not match
that of the current window background, ncurses updates only the
non-color attributes, first removing those that may have come from
the current background, and then adding attributes from the new
background.
If the new background's character is nonspacing, ncurses reuses the old
background character, except for one special case: ncurses treats a
background character value of zero (0) as a space.
If the terminal does not support color, or if color has not been
initialized with start_color(3x), ncurses ignores the new background
character's color attribute.
bkgrndset and wbkgrndset manipulate the background of the applicable
window, without updating the character cells as bkgrnd and wbkgrnd do;
only future writes reflect the updated background.
The getbkgrnd and wgetbkgrnd functions obtain the background character
and attribute pair of stdscr or the specified window and store it via
the wch pointer.
bkgrndset and wbkgrndset do not return a value.
The other functions return ERR upon failure and OK upon success. In
ncurses, failure occurs if
o a WINDOW pointer win is null, or
o a cchar_t pointer wch is null.
bkgrnd, bkgrndset, and getbkgrnd may be implemented as macros.
Unlike their counterparts in the non-wide configuration of ncurses,
getbkgrnd and wgetbkgrnd supply the background character and attribute
in a modifiable cchar_t parameter, not as the return value.
X/Open Curses, Issue 4 describes these functions. It specifies no
error conditions for them.
X/Open Curses does not provide details of how the rendition is updated.
This implementation follows the approach used in SVr4 curses.
curs_bkgd(3x) describes the corresponding functions in the non-wide
configuration of ncurses.
curses(3x), curs_add_wch(3x), curs_attr(3x)
ncurses 6.5 2024-09-22 curs_bkgrnd(3x)