-.\" $Id: curs_bkgd.3x,v 1.10 1996/07/20 23:48:30 tom Exp $
+.\"***************************************************************************
+.\" Copyright 2018-2019,2020 Thomas E. Dickey *
+.\" Copyright 1998-2015,2017 Free Software Foundation, Inc. *
+.\" *
+.\" Permission is hereby granted, free of charge, to any person obtaining a *
+.\" copy of this software and associated documentation files (the *
+.\" "Software"), to deal in the Software without restriction, including *
+.\" without limitation the rights to use, copy, modify, merge, publish, *
+.\" distribute, distribute with modifications, sublicense, and/or sell *
+.\" copies of the Software, and to permit persons to whom the Software is *
+.\" furnished to do so, subject to the following conditions: *
+.\" *
+.\" The above copyright notice and this permission notice shall be included *
+.\" in all copies or substantial portions of the Software. *
+.\" *
+.\" THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS *
+.\" OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF *
+.\" MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. *
+.\" IN NO EVENT SHALL THE ABOVE COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, *
+.\" DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR *
+.\" OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR *
+.\" THE USE OR OTHER DEALINGS IN THE SOFTWARE. *
+.\" *
+.\" Except as contained in this notice, the name(s) of the above copyright *
+.\" holders shall not be used in advertising or otherwise to promote the *
+.\" sale, use or other dealings in this Software without prior written *
+.\" authorization. *
+.\"***************************************************************************
+.\"
+.\" $Id: curs_bkgd.3x,v 1.31 2020/10/17 23:12:52 tom Exp $
+.de bP
+.ie n .IP \(bu 4
+.el .IP \(bu 2
+..
.TH curs_bkgd 3X ""
-.
.SH NAME
-\fBbkgdset\fR, \fBwbkgdset\fR, \fBbkgd\fR,
-\fBwbkgd\fR - \fBcurses\fR window background manipulation routines
-.
+\fBbkgdset\fR, \fBwbkgdset\fR,
+\fBbkgd\fR, \fBwbkgd\fR,
+\fBgetbkgd\fR \- \fBcurses\fR window background manipulation routines
.SH SYNOPSIS
\fB#include <curses.h>\fR
-
-\fBvoid bkgdset(const chtype ch);\fR
+.PP
+\fBvoid bkgdset(chtype \fP\fIch\fP\fB);\fR
.br
-\fBvoid wbkgdset(WINDOW *win, const chtype ch);\fR
+\fBvoid wbkgdset(WINDOW *\fP\fIwin, chtype \fP\fIch\fP\fB);\fR
+.sp
+\fBint bkgd(chtype \fP\fIch\fP\fB);\fR
.br
-\fBint bkgd(const chtype ch);\fR
+\fBint wbkgd(WINDOW *\fP\fIwin\fP\fB, chtype \fP\fIch\fP\fB);\fR
+.sp
+\fBchtype getbkgd(WINDOW *\fP\fIwin\fP\fB);\fR
.br
-\fBint wbkgd(WINDOW *win, const chtype ch);\fR
-.br
-\fBchtype getbkgd(WINDOW *win);\fR
-.br
-.
.SH DESCRIPTION
+.SS bkgdset
The \fBbkgdset\fR and \fBwbkgdset\fR routines manipulate the
background of the named window.
The window background is a \fBchtype\fR 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 \fBwaddch\fR. Both
-the character and attribute parts of the background are combined with
-the blank characters. The background becomes a property of the
+characters that are written into the window with \fBwaddch\fR.
+Both the character and attribute parts of the background are combined with
+the blank characters.
+The background becomes a property of the
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
+.PP
+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.
-
+.SS bkgd
+.PP
The \fBbkgd\fR and \fBwbkgd\fR functions
set the background property of the current or specified window
-and then apply this setting to every character position in that window:
-
-.RS
+and then apply this setting to every character position in that window.
+According to X/Open Curses, it should do this:
+.PP
+.bP
The rendition of every character on the screen is changed to
the new background rendition.
-
+.bP
Wherever the former background character
appears, it is changed to the new background character.
-.RE
-
+.PP
+Neither X/Open Curses nor the SVr4 manual pages give details about
+the way the rendition of characters on the screen is updated when
+\fBbkgd\fP or \fBwbkgd\fP is used to change the background character.
+.PP
+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:
+.bP
+The library first compares the \fIcharacter\fP,
+and if it matches the current character part of the background,
+it replaces that with the new background character.
+.bP
+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.
+.bP
+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.
+.bP
+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.
+.PP
+If the background's character value is zero, a space is assumed.
+.PP
+If the terminal does not support color,
+or if color has not been started with \fBstart_color\fP,
+the new background character's color attribute will be ignored.
+.SS getbkgd
+.PP
The \fBgetbkgd\fR function returns the given window's current background
character/attribute pair.
-.
.SH RETURN VALUE
-The routines \fBbkgd\fR and \fBwbkgd\fR return the integer \fBOK\fR.
-The SVr4.0 manual says "or a non-negative integer if \fBimmedok\fR is set",
-but this appears to be an error.
-.
+.PP
+These functions are described in the XSI Curses standard, Issue 4.
+It specifies that \fBbkgd\fR and \fBwbkgd\fR return \fBERR\fR on failure,
+but gives no failure conditions.
+.PP
+The routines \fBbkgd\fR and \fBwbkgd\fR return the integer \fBOK\fR,
+unless the library has not been initialized.
+.PP
+In contrast,
+the SVr4.0 manual says \fBbkgd\fR and \fBwbkgd\fR may return \fBOK\fP
+"or a non-negative integer if \fBimmedok\fR is set",
+which refers to the return value from \fBwrefresh\fP
+(used to implement the immediate repainting).
+The SVr4 curses \fBwrefresh\fP returns the number of characters
+written to the screen during the refresh.
+This implementation does not do that.
.SH NOTES
+.PP
Note that \fBbkgdset\fR and \fBbkgd\fR may be macros.
-.
+.PP
+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.
.SH PORTABILITY
-These functions are described in the XSI Curses standard, Issue 4. The draft
-does not include \fBconst\fR qualifiers on the arguments. The standard
-specifies that \fBbkgd\fR and \fBwbkgd\fR return \fBERR\fR, on failure. but
-gives no failure conditions.
-.
+.PP
+These functions are described in the XSI Curses standard, Issue 4
+(X/Open Curses).
.SH SEE ALSO
-\fBcurses\fR(3X), \fBcurs_addch\fR(3X), \fBcurs_outopts\fR(3X)
-.\"#
-.\"# The following sets edit modes for GNU EMACS
-.\"# Local Variables:
-.\"# mode:nroff
-.\"# fill-column:79
-.\"# End:
+.na
+.PP
+\fBcurses\fR(3X),
+\fBcurs_addch\fR(3X),
+\fBcurs_attr\fR(3X),
+\fBcurs_outopts\fR(3X)
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