ncurses 6.1 - patch 20181208

[ncurses.git] / man / curs_bkgd.3x

diff --git a/man/curs_bkgd.3x b/man/curs_bkgd.3x
index 2dc21e6a9c062025cd1e3cd2d9888752bbad4b3b..d93bbd4a995e1b5e197033f2c6814db266e68d4c 100644 (file)
--- a/man/curs_bkgd.3x
+++ b/man/curs_bkgd.3x
@@ -26,7 +26,7 @@
 .\" authorization.                                                           *
 .\"***************************************************************************
 .\"
 .\" authorization.                                                           *
 .\"***************************************************************************
 .\"

-.\" $Id: curs_bkgd.3x,v 1.26 2018/07/28 21:34:06 tom Exp $
+.\" $Id: curs_bkgd.3x,v 1.28 2018/12/09 00:45:05 tom Exp $

 .de bP
 .ie n  .IP \(bu 4
 .el    .IP \(bu 2
 .de bP
 .ie n  .IP \(bu 4
 .el    .IP \(bu 2


@@ -57,8 +57,7 @@ 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.
 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
 the blank characters.
 The background becomes a property of the
 character and moves with the character through any scrolling and


@@ -71,7 +70,8 @@ as the graphic rendition of the character put on the screen.
 .PP
 The \fBbkgd\fR and \fBwbkgd\fR functions
 set the background property of the current or specified window
 .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
 .PP
 .bP
 The rendition of every character on the screen is changed to


@@ -79,23 +79,72 @@ the new background rendition.
 .bP
 Wherever the former background character
 appears, it is changed to the new background character.
 .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.

 .SS getbkgd
 .PP
 The \fBgetbkgd\fR function returns the given window's current background
 character/attribute pair.
 .SH RETURN VALUE
 .PP
 .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.
 .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
 .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
 .SH SEE ALSO
 .na
 .PP