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<H1 class="no-header">curs_bkgd 3x 2024-04-20 ncurses 6.5 Library calls</H1>
<PRE>
<STRONG><A HREF="curs_bkgd.3x.html">curs_bkgd(3x)</A></STRONG> Library calls <STRONG><A HREF="curs_bkgd.3x.html">curs_bkgd(3x)</A></STRONG>
</PRE><H2><a name="h2-NAME">NAME</a></H2><PRE>
<STRONG>bkgdset</STRONG>, <STRONG>wbkgdset</STRONG>, <STRONG>bkgd</STRONG>, <STRONG>wbkgd</STRONG>, <STRONG>getbkgd</STRONG> - manipulate background of a
<EM>curses</EM> window of characters
</PRE><H2><a name="h2-SYNOPSIS">SYNOPSIS</a></H2><PRE>
<STRONG>#include</STRONG> <STRONG><curses.h></STRONG>
<STRONG>int</STRONG> <STRONG>bkgd(chtype</STRONG> <EM>ch</EM><STRONG>);</STRONG>
<STRONG>int</STRONG> <STRONG>wbkgd(WINDOW</STRONG> <STRONG>*</STRONG><EM>win</EM><STRONG>,</STRONG> <STRONG>chtype</STRONG> <EM>ch</EM><STRONG>);</STRONG>
<STRONG>void</STRONG> <STRONG>bkgdset(chtype</STRONG> <EM>ch</EM><STRONG>);</STRONG>
<STRONG>void</STRONG> <STRONG>wbkgdset(WINDOW</STRONG> <STRONG>*</STRONG><EM>win</EM><STRONG>,</STRONG> <STRONG>chtype</STRONG> <EM>ch</EM><STRONG>);</STRONG>
<STRONG>chtype</STRONG> <STRONG>getbkgd(WINDOW</STRONG> <STRONG>*</STRONG><EM>win</EM><STRONG>);</STRONG>
</PRE><H2><a name="h2-DESCRIPTION">DESCRIPTION</a></H2><PRE>
The <EM>background</EM> of a <EM>curses</EM> window (in the library's non-"wide"
configuration) is a <EM>chtype</EM> combining a set of attributes (see
<STRONG><A HREF="curs_attr.3x.html">curs_attr(3x)</A></STRONG>) with a character called the <EM>blank</EM> <EM>character.</EM>
The blank character is a spacing character that populates a window's
character cells when their contents are erased without replacement.
The background's attributes are combined with all non-blank characters
written to the window, as with the <STRONG><A HREF="curs_addch.3x.html">waddch(3x)</A></STRONG> and <STRONG><A HREF="curs_insch.3x.html">winsch(3x)</A></STRONG> families
of functions.
The blank character and attributes of the background combine with
characters written to the window as described below. 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.
</PRE><H3><a name="h3-bkgd_wbkgd">bkgd, wbkgd</a></H3><PRE>
<STRONG>bkgd</STRONG> and <STRONG>wbkgd</STRONG> set the background property of <STRONG>stdscr</STRONG> or the specified
window and then apply this setting to every character cell in that
window.
<STRONG>o</STRONG> The rendition of every character in the window changes to the new
background rendition.
<STRONG>o</STRONG> Wherever the former background character appears, it changes to the
new background character.
<EM>ncurses</EM> 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.
<STRONG>o</STRONG> <EM>ncurses</EM> first compares the cell's character to the previously
specified blank character; if they match, <EM>ncurses</EM> writes the new
blank character to the cell.
<STRONG>o</STRONG> <EM>ncurses</EM> 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.
<STRONG>o</STRONG> If the cell uses color, and its background color matches that of
the current window background, <EM>ncurses</EM> 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.
<STRONG>o</STRONG> If the cell uses color, and its background color does not match
that of the current window background, <EM>ncurses</EM> 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.
<EM>ncurses</EM> treats a background character value of zero (0) as a blank
character.
If the terminal does not support color, or if color has not been
initialized with <STRONG><A HREF="curs_color.3x.html">start_color(3x)</A></STRONG>, <EM>ncurses</EM> ignores the new background
character's color attribute.
</PRE><H3><a name="h3-bkgdset_wbkgdset">bkgdset, wbkgdset</a></H3><PRE>
<STRONG>bkgdset</STRONG> and <STRONG>wbkgdset</STRONG> manipulate the background of the applicable
window, without updating the character cells as <STRONG>bkgd</STRONG> and <STRONG>wbkgd</STRONG> do; only
future writes reflect the updated background.
</PRE><H3><a name="h3-getbkgd">getbkgd</a></H3><PRE>
<STRONG>getbkgd</STRONG> obtains the given window's background character and attribute
combination.
</PRE><H2><a name="h2-RETURN-VALUE">RETURN VALUE</a></H2><PRE>
Functions returning an <EM>int</EM> return <STRONG>OK</STRONG> on success. <STRONG>bkgd</STRONG> returns <STRONG>ERR</STRONG> if
the library has not been initialized. <STRONG>wbkgd</STRONG> and <STRONG>getbkgd</STRONG> return <STRONG>ERR</STRONG> if
a <EM>WINDOW</EM> pointer argument is null.
<STRONG>bkgdset</STRONG> and <STRONG>wbkgdset</STRONG> do not return a value.
<STRONG>getbkgd</STRONG> returns a window's background character and attribute
combination.
</PRE><H2><a name="h2-NOTES">NOTES</a></H2><PRE>
Unusually, there is no <STRONG>wgetbkgd</STRONG> function; <STRONG>getbkgd</STRONG> behaves as one would
expect <STRONG>wgetbkgd</STRONG> to, accepting a <EM>WINDOW</EM> pointer argument.
<STRONG>bkgd</STRONG> and <STRONG>bkgdset</STRONG> may be implemented as macros.
X/Open Curses mentions that the character part of the background must
be a single-byte value. <EM>ncurses</EM>, like SVr4 <EM>curses</EM>, checks to ensure
that, and will reuse the old background character if the check fails.
</PRE><H2><a name="h2-PORTABILITY">PORTABILITY</a></H2><PRE>
X/Open Curses, Issue 4 describes these functions. It specifies that
<STRONG>bkgd</STRONG>, <STRONG>wbkgd</STRONG>, and <STRONG>getbkgd</STRONG> return <STRONG>ERR</STRONG> on failure (in the case of the
last, this value is cast to <EM>chtype</EM>), but describes no failure
conditions.
The SVr4.0 manual says that <STRONG>bkgd</STRONG> and <STRONG>wbkgd</STRONG> may return <STRONG>OK</STRONG> "or a non-
negative integer if <STRONG>immedok</STRONG> is set", which refers to the return value
from <STRONG><A HREF="curs_refresh.3x.html">wrefresh(3x)</A></STRONG>, used to implement the immediate repainting. SVr4
<EM>curses</EM>'s <STRONG>wrefresh</STRONG> returns the number of characters written to the
screen during the refresh. <EM>ncurses</EM> does not do that.
Neither X/Open Curses nor the SVr4 manual pages detail how the
rendition of characters on the screen updates when <STRONG>bkgd</STRONG> or <STRONG>wbkgd</STRONG>
changes the background character. <EM>ncurses</EM>, like SVr4 <EM>curses</EM>, does not
(in its non-"wide" configuration) store the background and window
attribute contributions to each character cell separately.
</PRE><H2><a name="h2-SEE-ALSO">SEE ALSO</a></H2><PRE>
<STRONG><A HREF="curs_bkgrnd.3x.html">curs_bkgrnd(3x)</A></STRONG> describes the corresponding functions in the "wide"
configuration of <EM>ncurses</EM>.
<STRONG><A HREF="ncurses.3x.html">curses(3x)</A></STRONG>, <STRONG><A HREF="curs_addch.3x.html">curs_addch(3x)</A></STRONG>, <STRONG><A HREF="curs_attr.3x.html">curs_attr(3x)</A></STRONG>
ncurses 6.5 2024-04-20 <STRONG><A HREF="curs_bkgd.3x.html">curs_bkgd(3x)</A></STRONG>
</PRE>
<div class="nav">
<ul>
<li><a href="#h2-NAME">NAME</a></li>
<li><a href="#h2-SYNOPSIS">SYNOPSIS</a></li>
<li><a href="#h2-DESCRIPTION">DESCRIPTION</a>
<ul>
<li><a href="#h3-bkgd_wbkgd">bkgd, wbkgd</a></li>
<li><a href="#h3-bkgdset_wbkgdset">bkgdset, wbkgdset</a></li>
<li><a href="#h3-getbkgd">getbkgd</a></li>
</ul>
</li>
<li><a href="#h2-RETURN-VALUE">RETURN VALUE</a></li>
<li><a href="#h2-NOTES">NOTES</a></li>
<li><a href="#h2-PORTABILITY">PORTABILITY</a></li>
<li><a href="#h2-SEE-ALSO">SEE ALSO</a></li>
</ul>
</div>
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