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The background 79 becomes a property of the character and moves with it through any 80 scrolling and insert/delete line/character operations. 81 82 To the extent possible on a given terminal, the attribute part of the 83 background is displayed as the graphic rendition of the character put 84 on the screen. 85 86 87</PRE><H3><a name="h3-bkgd_wbkgd">bkgd, wbkgd</a></H3><PRE> 88 <STRONG>bkgd</STRONG> and <STRONG>wbkgd</STRONG> set the background property of <STRONG>stdscr</STRONG> or the specified 89 window and then apply this setting to every character cell in that 90 window. 91 92 <STRONG>o</STRONG> The rendition of every character in the window changes to the new 93 background rendition. 94 95 <STRONG>o</STRONG> Wherever the former background character appears, it changes to the 96 new background character. 97 98 <EM>ncurses</EM> updates the rendition of each character cell by comparing the 99 character, non-color attributes, and colors. The library applies to 100 following procedure to each cell in the window, whether or not it is 101 blank. 102 103 <STRONG>o</STRONG> <EM>ncurses</EM> first compares the cell's character to the previously 104 specified blank character; if they match, <EM>ncurses</EM> writes the new 105 blank character to the cell. 106 107 <STRONG>o</STRONG> <EM>ncurses</EM> then checks if the cell uses color, that is, its color pair 108 value is nonzero. If not, it simply replaces the attributes and 109 color pair in the cell with those from the new background 110 character. 111 112 <STRONG>o</STRONG> If the cell uses color, and its background color matches that of 113 the current window background, <EM>ncurses</EM> removes attributes that may 114 have come from the current background and adds those from the new 115 background. It finishes by setting the cell's background to use 116 the new window background color. 117 118 <STRONG>o</STRONG> If the cell uses color, and its background color does not match 119 that of the current window background, <EM>ncurses</EM> updates only the 120 non-color attributes, first removing those that may have come from 121 the current background, and then adding attributes from the new 122 background. 123 124 <EM>ncurses</EM> treats a background character value of zero (0) as a blank 125 character. 126 127 If the terminal does not support color, or if color has not been 128 initialized with <STRONG><A HREF="curs_color.3x.html">start_color(3x)</A></STRONG>, <EM>ncurses</EM> ignores the new background 129 character's color attribute. 130 131 132</PRE><H3><a name="h3-bkgdset_wbkgdset">bkgdset, wbkgdset</a></H3><PRE> 133 <STRONG>bkgdset</STRONG> and <STRONG>wbkgdset</STRONG> manipulate the background of the applicable 134 window, without updating the character cells as <STRONG>bkgd</STRONG> and <STRONG>wbkgd</STRONG> do; only 135 future writes reflect the updated background. 136 137 138</PRE><H3><a name="h3-getbkgd">getbkgd</a></H3><PRE> 139 <STRONG>getbkgd</STRONG> obtains the given window's background character and attribute 140 combination. 141 142 143</PRE><H2><a name="h2-RETURN-VALUE">RETURN VALUE</a></H2><PRE> 144 Functions returning an <EM>int</EM> return <STRONG>OK</STRONG> on success. <STRONG>bkgd</STRONG> returns <STRONG>ERR</STRONG> if 145 the library has not been initialized. <STRONG>wbkgd</STRONG> and <STRONG>getbkgd</STRONG> return <STRONG>ERR</STRONG> if 146 a <EM>WINDOW</EM> pointer argument is null. 147 148 <STRONG>bkgdset</STRONG> and <STRONG>wbkgdset</STRONG> do not return a value. 149 150 <STRONG>getbkgd</STRONG> returns a window's background character and attribute 151 combination. 152 153 154</PRE><H2><a name="h2-NOTES">NOTES</a></H2><PRE> 155 Unusually, there is no <STRONG>wgetbkgd</STRONG> function; <STRONG>getbkgd</STRONG> behaves as one would 156 expect <STRONG>wgetbkgd</STRONG> to, accepting a <EM>WINDOW</EM> pointer argument. 157 158 <STRONG>bkgd</STRONG> and <STRONG>bkgdset</STRONG> may be implemented as macros. 159 160 X/Open Curses mentions that the character part of the background must 161 be a single-byte value. <EM>ncurses</EM>, like SVr4 <EM>curses</EM>, checks to ensure 162 that, and will reuse the old background character if the check fails. 163 164 165</PRE><H2><a name="h2-PORTABILITY">PORTABILITY</a></H2><PRE> 166 X/Open Curses, Issue 4 describes these functions. It specifies that 167 <STRONG>bkgd</STRONG>, <STRONG>wbkgd</STRONG>, and <STRONG>getbkgd</STRONG> return <STRONG>ERR</STRONG> on failure (in the case of the 168 last, this value is cast to <EM>chtype</EM>), but describes no failure 169 conditions. 170 171 The SVr4.0 manual says that <STRONG>bkgd</STRONG> and <STRONG>wbkgd</STRONG> may return <STRONG>OK</STRONG> "or a non- 172 negative integer if <STRONG>immedok</STRONG> is set", which refers to the return value 173 from <STRONG><A HREF="curs_refresh.3x.html">wrefresh(3x)</A></STRONG>, used to implement the immediate repainting. SVr4 174 <EM>curses</EM>'s <STRONG>wrefresh</STRONG> returns the number of characters written to the 175 screen during the refresh. <EM>ncurses</EM> does not do that. 176 177 Neither X/Open Curses nor the SVr4 manual pages detail how the 178 rendition of characters on the screen updates when <STRONG>bkgd</STRONG> or <STRONG>wbkgd</STRONG> 179 changes the background character. <EM>ncurses</EM>, like SVr4 <EM>curses</EM>, does not 180 (in its non-"wide" configuration) store the background and window 181 attribute contributions to each character cell separately. 182 183 184</PRE><H2><a name="h2-SEE-ALSO">SEE ALSO</a></H2><PRE> 185 <STRONG><A HREF="curs_bkgrnd.3x.html">curs_bkgrnd(3x)</A></STRONG> describes the corresponding functions in the "wide" 186 configuration of <EM>ncurses</EM>. 187 188 <STRONG><A HREF="ncurses.3x.html">curses(3x)</A></STRONG>, <STRONG><A HREF="curs_addch.3x.html">curs_addch(3x)</A></STRONG>, <STRONG><A HREF="curs_attr.3x.html">curs_attr(3x)</A></STRONG> 189 190 191 192ncurses 6.5 2024-04-20 <STRONG><A HREF="curs_bkgd.3x.html">curs_bkgd(3x)</A></STRONG> 193</PRE> 194<div class="nav"> 195<ul> 196<li><a href="#h2-NAME">NAME</a></li> 197<li><a href="#h2-SYNOPSIS">SYNOPSIS</a></li> 198<li><a href="#h2-DESCRIPTION">DESCRIPTION</a> 199<ul> 200<li><a href="#h3-bkgd_wbkgd">bkgd, wbkgd</a></li> 201<li><a href="#h3-bkgdset_wbkgdset">bkgdset, wbkgdset</a></li> 202<li><a href="#h3-getbkgd">getbkgd</a></li> 203</ul> 204</li> 205<li><a href="#h2-RETURN-VALUE">RETURN VALUE</a></li> 206<li><a href="#h2-NOTES">NOTES</a></li> 207<li><a href="#h2-PORTABILITY">PORTABILITY</a></li> 208<li><a href="#h2-SEE-ALSO">SEE ALSO</a></li> 209</ul> 210</div> 211</BODY> 212</HTML> 213