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* @Id: curs_bkgrnd.3x,v 1.60 2025/08/23 22:39:20 tom Exp @
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<TITLE>curs_bkgrnd 3x 2025-08-23 ncurses 6.6 Library calls</TITLE>
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<link rel="author" href="mailto:bug-ncurses@gnu.org">
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<H1 class="no-header">curs_bkgrnd 3x 2025-08-23 ncurses 6.6 Library calls</H1>
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<PRE>
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<STRONG><A HREF="curs_bkgrnd.3x.html">curs_bkgrnd(3x)</A></STRONG> Library calls <STRONG><A HREF="curs_bkgrnd.3x.html">curs_bkgrnd(3x)</A></STRONG>
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</PRE><H2><a name="h2-NAME">NAME</a></H2><PRE>
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<STRONG>bkgrnd</STRONG>, <STRONG>wbkgrnd</STRONG>, <STRONG>bkgrndset</STRONG>, <STRONG>wbkgrndset</STRONG>, <STRONG>getbkgrnd</STRONG>, <STRONG>wgetbkgrnd</STRONG> -
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manipulate background of a <EM>curses</EM> window of wide characters
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</PRE><H2><a name="h2-SYNOPSIS">SYNOPSIS</a></H2><PRE>
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<STRONG>#include</STRONG> <STRONG><curses.h></STRONG>
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<STRONG>int</STRONG> <STRONG>bkgrnd(const</STRONG> <STRONG>cchar_t</STRONG> <STRONG>*</STRONG><EM>wch</EM><STRONG>);</STRONG>
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<STRONG>int</STRONG> <STRONG>wbkgrnd(WINDOW</STRONG> <STRONG>*</STRONG><EM>win</EM><STRONG>,</STRONG> <STRONG>const</STRONG> <STRONG>cchar_t</STRONG> <STRONG>*</STRONG><EM>wch</EM><STRONG>);</STRONG>
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<STRONG>void</STRONG> <STRONG>bkgrndset(const</STRONG> <STRONG>cchar_t</STRONG> <STRONG>*</STRONG><EM>wch</EM><STRONG>);</STRONG>
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<STRONG>void</STRONG> <STRONG>wbkgrndset(WINDOW</STRONG> <STRONG>*</STRONG><EM>win</EM><STRONG>,</STRONG> <STRONG>const</STRONG> <STRONG>cchar_t</STRONG> <STRONG>*</STRONG><EM>wch</EM><STRONG>);</STRONG>
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<STRONG>int</STRONG> <STRONG>getbkgrnd(cchar_t</STRONG> <STRONG>*</STRONG><EM>wch</EM><STRONG>);</STRONG>
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<STRONG>int</STRONG> <STRONG>wgetbkgrnd(WINDOW</STRONG> <STRONG>*</STRONG><EM>win</EM><STRONG>,</STRONG> <STRONG>cchar_t</STRONG> <STRONG>*</STRONG><EM>wch</EM><STRONG>);</STRONG>
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</PRE><H2><a name="h2-DESCRIPTION">DESCRIPTION</a></H2><PRE>
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Every <EM>curses</EM> window has a <EM>background</EM> <EM>character</EM> property: in the
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library's wide configuration, it is a <EM>curses</EM> complex character
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(<EM>cchar</EM><STRONG>_</STRONG><EM>t</EM>) that combines a set of attributes (and, if colors are
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enabled, a color pair identifier) with a character code. When erasing
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(parts of) a window, <EM>curses</EM> replaces the erased cells with the
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background character.
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<EM>curses</EM> also uses the background character when writing characters to a
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populated window.
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<STRONG>o</STRONG> The attribute part of the background character combines with all
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non-blank character cells in the window, as populated by the
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<STRONG><A HREF="curs_add_wch.3x.html">wadd_wch(3x)</A></STRONG> and <STRONG><A HREF="curs_ins_wch.3x.html">wins_wch(3x)</A></STRONG> families of functions (and those that
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call them).
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<STRONG>o</STRONG> Both the character code and attributes of the background character
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combine with blank character cells in the window.
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The background character's set of attributes becomes a property of the
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character cell and move with it through any scrolling and insert/delete
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line/character operations. To the extent possible on the terminal
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type, <EM>curses</EM> displays the attributes of the background character as the
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graphic rendition of a character cell on the display.
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</PRE><H3><a name="h3-bkgrnd_wbkgrnd">bkgrnd, wbkgrnd</a></H3><PRE>
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<STRONG>bkgrnd</STRONG> and <STRONG>wbkgrnd</STRONG> set the background property of <STRONG>stdscr</STRONG> or the
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specified window and then apply this setting to every character cell in
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that window.
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<STRONG>o</STRONG> The rendition of every character in the window changes to the new
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background rendition.
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<STRONG>o</STRONG> Wherever the former background character appears, it changes to the
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new background character.
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<EM>ncurses</EM> updates the rendition of each character cell by comparing the
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character, non-color attributes, and color pair selection. The library
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applies to following procedure to each cell in the window, whether or
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not it is blank.
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<STRONG>o</STRONG> <EM>ncurses</EM> first compares the cell's character to the previously
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specified background character; if they match, <EM>ncurses</EM> writes the
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new background character to the cell.
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<STRONG>o</STRONG> <EM>ncurses</EM> then checks whether the cell uses color; that is, its color
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pair value is nonzero. If not, it simply replaces the attributes
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and color pair in the cell with those from the new background
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character.
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<STRONG>o</STRONG> If the cell uses color, and its background color matches that of
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the current window background, <EM>ncurses</EM> removes attributes that may
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have come from the current background and adds those from the new
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background. It finishes by setting the cell's background to use
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the new window background color.
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<STRONG>o</STRONG> If the cell uses color, and its background color does not match
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that of the current window background, <EM>ncurses</EM> updates only the
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non-color attributes, first removing those that may have come from
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the current background, and then adding attributes from the new
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background.
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If the new background's character is non-spacing, <EM>ncurses</EM> reuses the
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old background character, except for one special case: <EM>ncurses</EM> treats a
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background character code of zero (0) as a space.
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If the terminal does not support color, or if color has not been
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initialized with <STRONG><A HREF="curs_color.3x.html">start_color(3x)</A></STRONG>, <EM>ncurses</EM> ignores the new background
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character's color pair selection.
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</PRE><H3><a name="h3-bkgrndset_wbkgrndset">bkgrndset, wbkgrndset</a></H3><PRE>
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<STRONG>bkgrndset</STRONG> and <STRONG>wbkgrndset</STRONG> manipulate the background of the applicable
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window, without updating the character cells as <STRONG>bkgrnd</STRONG> and <STRONG>wbkgrnd</STRONG> do;
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only future writes reflect the updated background.
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</PRE><H3><a name="h3-getbkgrnd_wgetbkgrnd">getbkgrnd, wgetbkgrnd</a></H3><PRE>
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<STRONG>getbkgrnd</STRONG> and <STRONG>wgetbkgrnd</STRONG> respectively obtain <STRONG>stdscr</STRONG>'s or the given
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window's background character, attributes, and color pair, and store it
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in their <EM>wch</EM> argument.
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</PRE><H2><a name="h2-RETURN-VALUE">RETURN VALUE</a></H2><PRE>
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<STRONG>bkgrndset</STRONG> and <STRONG>wbkgrndset</STRONG> do not return a value.
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Functions returning an <EM>int</EM> return <STRONG>ERR</STRONG> upon failure and <STRONG>OK</STRONG> upon success.
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In <EM>ncurses</EM>, failure occurs if
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<STRONG>o</STRONG> the <EM>curses</EM> screen has not been initialized,
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<STRONG>o</STRONG> <EM>win</EM> is <EM>NULL</EM>, or
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<STRONG>o</STRONG> <EM>wch</EM> is <EM>NULL</EM>.
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</PRE><H2><a name="h2-NOTES">NOTES</a></H2><PRE>
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<STRONG>bkgrnd</STRONG>, <STRONG>bkgrndset</STRONG>, and <STRONG>getbkgrnd</STRONG> may be implemented as macros.
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Unlike their counterparts in the non-wide-character configuration of
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<EM>ncurses</EM>, <STRONG>getbkgrnd</STRONG> and <STRONG>wgetbkgrnd</STRONG> store the background character in a
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modifiable <EM>cchar</EM><STRONG>_</STRONG><EM>t</EM> parameter, rather than supplying it as the return
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value.
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</PRE><H2><a name="h2-PORTABILITY">PORTABILITY</a></H2><PRE>
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X/Open Curses Issue 4 describes these functions. It specifies no error
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conditions for them.
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X/Open Curses does not provide details of how the rendition is updated.
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<EM>ncurses</EM> follows the approach used in SVr4 <EM>curses</EM>'s non-wide functions
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for manipulating the window background.
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</PRE><H2><a name="h2-HISTORY">HISTORY</a></H2><PRE>
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X/Open Curses Issue 4 (1995) initially specified these functions.
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</PRE><H2><a name="h2-SEE-ALSO">SEE ALSO</a></H2><PRE>
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<STRONG><A HREF="curs_bkgd.3x.html">curs_bkgd(3x)</A></STRONG> describes the corresponding functions in the non-wide-
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character configuration of <EM>ncurses</EM>.
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<STRONG><A HREF="ncurses.3x.html">curses(3x)</A></STRONG>, <STRONG><A HREF="curs_add_wch.3x.html">curs_add_wch(3x)</A></STRONG>, <STRONG><A HREF="curs_attr.3x.html">curs_attr(3x)</A></STRONG>
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ncurses 6.6 2025-08-23 <STRONG><A HREF="curs_bkgrnd.3x.html">curs_bkgrnd(3x)</A></STRONG>
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</PRE>
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<div class="nav">
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<ul>
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<li><a href="#h2-NAME">NAME</a></li>
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<li><a href="#h2-SYNOPSIS">SYNOPSIS</a></li>
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<li><a href="#h2-DESCRIPTION">DESCRIPTION</a>
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<ul>
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<li><a href="#h3-bkgrnd_wbkgrnd">bkgrnd, wbkgrnd</a></li>
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<li><a href="#h3-bkgrndset_wbkgrndset">bkgrndset, wbkgrndset</a></li>
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<li><a href="#h3-getbkgrnd_wgetbkgrnd">getbkgrnd, wgetbkgrnd</a></li>
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</ul>
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</li>
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<li><a href="#h2-RETURN-VALUE">RETURN VALUE</a></li>
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<li><a href="#h2-NOTES">NOTES</a></li>
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<li><a href="#h2-PORTABILITY">PORTABILITY</a></li>
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<li><a href="#h2-HISTORY">HISTORY</a></li>
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<li><a href="#h2-SEE-ALSO">SEE ALSO</a></li>
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</ul>
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