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* @Id: curs_bkgd.3x,v 1.61 2024/04/20 18:54:36 tom Exp @

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<TITLE>curs_bkgd 3x 2024-04-20 ncurses 6.5 Library calls</TITLE>

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<H1 class="no-header">curs_bkgd 3x 2024-04-20 ncurses 6.5 Library calls</H1>

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<PRE>

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<A HREF="curs_bkgd.3x.html">curs_bkgd(3x)</A> Library calls <A HREF="curs_bkgd.3x.html">curs_bkgd(3x)</A>

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</PRE><H2><a name="h2-NAME">NAME</a></H2><PRE>

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bkgdset, wbkgdset, bkgd, wbkgd, getbkgd - manipulate background of a

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curses window of characters

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</PRE><H2><a name="h2-SYNOPSIS">SYNOPSIS</a></H2><PRE>

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#include <curses.h>

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int bkgd(chtype ch);

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int wbkgd(WINDOW *win, chtype ch);

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void bkgdset(chtype ch);

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void wbkgdset(WINDOW *win, chtype ch);

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chtype getbkgd(WINDOW *win);

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</PRE><H2><a name="h2-DESCRIPTION">DESCRIPTION</a></H2><PRE>

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The background of a curses window (in the library's non-"wide"

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configuration) is a chtype combining a set of attributes (see

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<A HREF="curs_attr.3x.html">curs_attr(3x)</A>) with a character called the blank character.

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The blank character is a spacing character that populates a window's

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character cells when their contents are erased without replacement.

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The background's attributes are combined with all non-blank characters

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written to the window, as with the <A HREF="curs_addch.3x.html">waddch(3x)</A> and <A HREF="curs_insch.3x.html">winsch(3x)</A> families

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of functions.

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The blank character and attributes of the background combine with

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characters written to the window as described below. The background

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becomes a property of the character and moves with it through any

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scrolling and insert/delete line/character operations.

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To the extent possible on a given terminal, the attribute part of the

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background is displayed as the graphic rendition of the character put

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on the screen.

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</PRE><H3><a name="h3-bkgd_wbkgd">bkgd, wbkgd</a></H3><PRE>

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bkgd and wbkgd set the background property of stdscr or the specified

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window and then apply this setting to every character cell in that

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window.

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o The rendition of every character in the window changes to the new

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background rendition.

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o Wherever the former background character appears, it changes to the

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new background character.

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ncurses updates the rendition of each character cell by comparing the

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character, non-color attributes, and colors. The library applies to

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following procedure to each cell in the window, whether or not it is

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blank.

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o ncurses first compares the cell's character to the previously

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specified blank character; if they match, ncurses writes the new

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blank character to the cell.

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o ncurses then checks if the cell uses color, that is, its color pair

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value is nonzero. If not, it simply replaces the attributes and

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color pair in the cell with those from the new background

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character.

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o If the cell uses color, and its background color matches that of

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the current window background, ncurses 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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o If the cell uses color, and its background color does not match

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that of the current window background, ncurses 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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ncurses treats a background character value of zero (0) as a blank

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character.

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If the terminal does not support color, or if color has not been

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initialized with <A HREF="curs_color.3x.html">start_color(3x)</A>, ncurses ignores the new background

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character's color attribute.

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</PRE><H3><a name="h3-bkgdset_wbkgdset">bkgdset, wbkgdset</a></H3><PRE>

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bkgdset and wbkgdset manipulate the background of the applicable

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window, without updating the character cells as bkgd and wbkgd do; only

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future writes reflect the updated background.

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</PRE><H3><a name="h3-getbkgd">getbkgd</a></H3><PRE>

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getbkgd obtains the given window's background character and attribute

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combination.

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</PRE><H2><a name="h2-RETURN-VALUE">RETURN VALUE</a></H2><PRE>

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Functions returning an int return OK on success. bkgd returns ERR if

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the library has not been initialized. wbkgd and getbkgd return ERR if

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a WINDOW pointer argument is null.

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bkgdset and wbkgdset do not return a value.

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getbkgd returns a window's background character and attribute

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combination.

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</PRE><H2><a name="h2-NOTES">NOTES</a></H2><PRE>

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Unusually, there is no wgetbkgd function; getbkgd behaves as one would

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expect wgetbkgd to, accepting a WINDOW pointer argument.

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bkgd and bkgdset may be implemented as macros.

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X/Open Curses mentions that the character part of the background must

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be a single-byte value. ncurses, like SVr4 curses, checks to ensure

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that, and will reuse the old background character if the check fails.

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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 that

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bkgd, wbkgd, and getbkgd return ERR on failure (in the case of the

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last, this value is cast to chtype), but describes no failure

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conditions.

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The SVr4.0 manual says that bkgd and wbkgd may return OK "or a non-

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negative integer if immedok is set", which refers to the return value

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from <A HREF="curs_refresh.3x.html">wrefresh(3x)</A>, used to implement the immediate repainting. SVr4

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curses's wrefresh returns the number of characters written to the

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screen during the refresh. ncurses does not do that.

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Neither X/Open Curses nor the SVr4 manual pages detail how the

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rendition of characters on the screen updates when bkgd or wbkgd

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changes the background character. ncurses, like SVr4 curses, does not

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(in its non-"wide" configuration) store the background and window

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attribute contributions to each character cell separately.

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</PRE><H2><a name="h2-SEE-ALSO">SEE ALSO</a></H2><PRE>

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<A HREF="curs_bkgrnd.3x.html">curs_bkgrnd(3x)</A> describes the corresponding functions in the "wide"

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configuration of ncurses.

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<A HREF="ncurses.3x.html">curses(3x)</A>, <A HREF="curs_addch.3x.html">curs_addch(3x)</A>, <A HREF="curs_attr.3x.html">curs_attr(3x)</A>

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ncurses 6.5 2024-04-20 <A HREF="curs_bkgd.3x.html">curs_bkgd(3x)</A>

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</PRE>

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<ul>

<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-bkgd_wbkgd">bkgd, wbkgd</a></li>

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<li><a href="#h3-bkgdset_wbkgdset">bkgdset, wbkgdset</a></li>

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<li><a href="#h3-getbkgd">getbkgd</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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</ul>

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</div>

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