.\"***************************************************************************
-.\" Copyright (c) 1998-2017,2018 Free Software Foundation, Inc. *
+.\" Copyright 2018-2020,2021 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 *
.\" authorization. *
.\"***************************************************************************
.\"
-.\" $Id: curs_bkgd.3x,v 1.26 2018/07/28 21:34:06 tom Exp $
+.\" $Id: curs_bkgd.3x,v 1.32 2021/06/17 21:30:22 tom Exp $
.de bP
.ie n .IP \(bu 4
.el .IP \(bu 2
\fBvoid bkgdset(chtype \fP\fIch\fP\fB);\fR
.br
\fBvoid wbkgdset(WINDOW *\fP\fIwin, chtype \fP\fIch\fP\fB);\fR
-.br
+.sp
\fBint bkgd(chtype \fP\fIch\fP\fB);\fR
.br
\fBint wbkgd(WINDOW *\fP\fIwin\fP\fB, chtype \fP\fIch\fP\fB);\fR
-.br
+.sp
\fBchtype getbkgd(WINDOW *\fP\fIwin\fP\fB);\fR
.br
.SH DESCRIPTION
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
+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
.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:
+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
.bP
Wherever the former background character
appears, it is changed to the new background character.
+.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
.PP
-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.
+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
.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.
+These functions are described in the XSI Curses standard, Issue 4
+(X/Open Curses).
.SH SEE ALSO
.na
.PP
projects / ncurses.git / blobdiff