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- * @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 @
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</PRE><H3><a name="h3-bkgd">bkgd</a></H3><PRE>
The <STRONG>bkgd</STRONG> and <STRONG>wbkgd</STRONG> functions set the background property of the current
or specified window and then apply this setting to every character
- position in that window:
+ position in that window. According to X/Open Curses, it should do
+ this:
- <STRONG>o</STRONG> The rendition of every character on the screen is changed to the
+ <STRONG>o</STRONG> The rendition of every character on the screen is changed to the
new background rendition.
- <STRONG>o</STRONG> Wherever the former background character appears, it is changed to
+ <STRONG>o</STRONG> Wherever the former background character appears, it is changed to
the new background character.
+ Neither X/Open Curses nor the SVr4 manual pages give details about the
+ way the rendition of characters on the screen is updated when <STRONG>bkgd</STRONG> or
+ <STRONG>wbkgd</STRONG> is used to change the background character.
+
+ 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 col-
+ ors contained in the background. For each cell in the window, whether
+ or not it is blank:
+
+ <STRONG>o</STRONG> The library first compares the <EM>character</EM>, and if it matches the
+ current character part of the background, it replaces that with the
+ new background character.
+
+ <STRONG>o</STRONG> 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 char-
+ acter.
+
+ <STRONG>o</STRONG> 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 back-
+ ground.
+
+ <STRONG>o</STRONG> 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 cur-
+ rent background, and then adding attributes from the new back-
+ ground.
+
</PRE><H3><a name="h3-getbkgd">getbkgd</a></H3><PRE>
The <STRONG>getbkgd</STRONG> function returns the given window's current background
</PRE><H2><a name="h2-RETURN-VALUE">RETURN VALUE</a></H2><PRE>
- The routines <STRONG>bkgd</STRONG> and <STRONG>wbkgd</STRONG> return the integer <STRONG>OK</STRONG>. The SVr4.0 manual
- says "or a non-negative integer if <STRONG>immedok</STRONG> is set", but this appears to
- be an error.
+ These functions are described in the XSI Curses standard, Issue 4. It
+ specifies that <STRONG>bkgd</STRONG> and <STRONG>wbkgd</STRONG> return <STRONG>ERR</STRONG> on failure, but gives no fail-
+ ure conditions.
+
+ The routines <STRONG>bkgd</STRONG> and <STRONG>wbkgd</STRONG> return the integer <STRONG>OK</STRONG>, unless the library
+ has not been initialized.
+
+ In contrast, the SVr4.0 manual says <STRONG>bkgd</STRONG> and <STRONG>wbkgd</STRONG> may return <STRONG>OK</STRONG> "or a
+ non-negative integer if <STRONG>immedok</STRONG> is set", which refers to the return
+ value from <STRONG>wrefresh</STRONG> (used to implement the immediate repainting). The
+ SVr4 curses <STRONG>wrefresh</STRONG> returns the number of characters written to the
+ screen during the refresh. This implementation does not do that.
</PRE><H2><a name="h2-NOTES">NOTES</a></H2><PRE>
Note that <STRONG>bkgdset</STRONG> and <STRONG>bkgd</STRONG> may be macros.
+ 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.
+
</PRE><H2><a name="h2-PORTABILITY">PORTABILITY</a></H2><PRE>
- These functions are described in the XSI Curses standard, Issue 4. It
- specifies that <STRONG>bkgd</STRONG> and <STRONG>wbkgd</STRONG> return <STRONG>ERR</STRONG> on failure, but gives no fail-
- ure conditions.
+ These functions are described in the XSI Curses standard, Issue 4
+ (X/Open Curses).
</PRE><H2><a name="h2-SEE-ALSO">SEE ALSO</a></H2><PRE>
projects / ncurses.git / blobdiff