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30 * Author: Thomas E. Dickey
31 * @Id: new_pair.3x,v 1.19 2022/02/12 20:03:40 tom Exp @
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43 <H1 class="no-header">new_pair 3x</H1>
45 <STRONG><A HREF="new_pair.3x.html">new_pair(3x)</A></STRONG> <STRONG><A HREF="new_pair.3x.html">new_pair(3x)</A></STRONG>
50 </PRE><H2><a name="h2-NAME">NAME</a></H2><PRE>
51 <STRONG>alloc_pair</STRONG>, <STRONG>find_pair</STRONG>, <STRONG>free_pair</STRONG> - new curses color-pair functions
54 </PRE><H2><a name="h2-SYNOPSIS">SYNOPSIS</a></H2><PRE>
55 <STRONG>#include</STRONG> <STRONG><curses.h></STRONG>
57 <STRONG>int</STRONG> <STRONG>alloc_pair(int</STRONG> <EM>fg</EM><STRONG>,</STRONG> <STRONG>int</STRONG> <EM>bg</EM><STRONG>);</STRONG>
58 <STRONG>int</STRONG> <STRONG>find_pair(int</STRONG> <EM>fg</EM><STRONG>,</STRONG> <STRONG>int</STRONG> <EM>bg</EM><STRONG>);</STRONG>
59 <STRONG>int</STRONG> <STRONG>free_pair(int</STRONG> <EM>pair</EM><STRONG>);</STRONG>
62 </PRE><H2><a name="h2-DESCRIPTION">DESCRIPTION</a></H2><PRE>
63 These functions are an extension to the curses library. They permit an
64 application to dynamically allocate a color pair using the
65 foreground/background colors rather than assign a fixed color pair
66 number, and return an unused pair to the pool.
68 The number of colors may be related to the number of possible color
69 pairs for a given terminal, or it may not:
71 <STRONG>o</STRONG> While almost all terminals allow setting the color <EM>attributes</EM>
72 independently, it is unlikely that your terminal allows you to
73 modify the attributes of a given character cell without rewriting
74 it. That is, the foreground and background colors are applied as a
77 <STRONG>o</STRONG> Color pairs are the curses library's way of managing a color
78 palette on a terminal. If the library does not keep track of the
79 <EM>combinations</EM> of colors which are displayed, it will be inefficient.
81 <STRONG>o</STRONG> For simple terminal emulators with only a few dozen color
82 combinations, it is convenient to use the maximum number of
83 combinations as the limit on color pairs:
85 <STRONG>COLORS</STRONG> <EM>*</EM> <STRONG>COLORS</STRONG>
87 <STRONG>o</STRONG> Terminals which support <EM>default</EM> <EM>colors</EM> distinct from "ANSI colors"
88 add to the possible combinations, producing this total:
90 <EM>(</EM> <STRONG>COLORS</STRONG> <EM>+</EM> <EM>1</EM> <EM>)</EM> <EM>*</EM> <EM>(</EM> <STRONG>COLORS</STRONG> <EM>+</EM> <EM>1</EM> <EM>)</EM>
92 <STRONG>o</STRONG> An application might use up to a few dozen color pairs to implement
93 a predefined color scheme.
95 Beyond that lies in the realm of programs using the foreground and
96 background colors for "ASCII art" (or some other non-textual
99 Also beyond those few dozen pairs, the required size for a table to
100 represent the combinations grows rapidly with an increasing number
103 These functions allow a developer to let the screen library manage
107 </PRE><H3><a name="h3-alloc_pair">alloc_pair</a></H3><PRE>
108 The <STRONG>alloc_pair</STRONG> function accepts parameters for foreground and
109 background color, and checks if that color combination is already
110 associated with a color pair.
112 <STRONG>o</STRONG> If the combination already exists, <STRONG>alloc_pair</STRONG> returns the existing
115 <STRONG>o</STRONG> If the combination does not exist, <STRONG>alloc_pair</STRONG> allocates a new color
116 pair and returns that.
118 <STRONG>o</STRONG> If the table fills up, <STRONG>alloc_pair</STRONG> discards the least-recently
119 allocated entry using <STRONG>free_pair</STRONG> and allocates a new color pair.
121 All of the color pairs are allocated from a table of possible color
122 pairs. The size of the table is determined by the terminfo <STRONG>pairs</STRONG>
123 capability. The table is shared with <STRONG>init_pair</STRONG>; in fact <STRONG>alloc_pair</STRONG>
124 calls <STRONG>init_pair</STRONG> after updating the ncurses library's fast index to the
125 colors versus color pairs.
128 </PRE><H3><a name="h3-find_pair">find_pair</a></H3><PRE>
129 The <STRONG>find_pair</STRONG> function accepts parameters for foreground and background
130 color, and checks if that color combination is already associated with
131 a color pair, returning the pair number if it has been allocated.
132 Otherwise it returns -1.
135 </PRE><H3><a name="h3-free_pair">free_pair</a></H3><PRE>
136 Marks the given color pair as unused, i.e., like color pair 0.
139 </PRE><H2><a name="h2-RETURN-VALUE">RETURN VALUE</a></H2><PRE>
140 The <STRONG>alloc_pair</STRONG> function returns a color pair number in the range 1
141 through <STRONG>COLOR_PAIRS</STRONG>-1, unless it encounters an error updating its fast
142 index to the color pair values, preventing it from allocating a color
143 pair. In that case, it returns -1.
145 The <STRONG>find_pair</STRONG> function returns a color pair number if the given color
146 combination has been associated with a color pair, or -1 if not.
148 Likewise, <STRONG>free_pair</STRONG> returns <STRONG>OK</STRONG> unless it encounters an error updating
149 the fast index or if no such color pair is in use.
152 </PRE><H2><a name="h2-PORTABILITY">PORTABILITY</a></H2><PRE>
153 These routines are specific to ncurses. They were not supported on
154 Version 7, BSD or System V implementations. It is recommended that any
155 code depending on them be conditioned using NCURSES_VERSION.
158 </PRE><H2><a name="h2-SEE-ALSO">SEE ALSO</a></H2><PRE>
159 <STRONG><A HREF="curs_color.3x.html">curs_color(3x)</A></STRONG>.
162 </PRE><H2><a name="h2-AUTHOR">AUTHOR</a></H2><PRE>
167 <STRONG><A HREF="new_pair.3x.html">new_pair(3x)</A></STRONG>
171 <li><a href="#h2-NAME">NAME</a></li>
172 <li><a href="#h2-SYNOPSIS">SYNOPSIS</a></li>
173 <li><a href="#h2-DESCRIPTION">DESCRIPTION</a>
175 <li><a href="#h3-alloc_pair">alloc_pair</a></li>
176 <li><a href="#h3-find_pair">find_pair</a></li>
177 <li><a href="#h3-free_pair">free_pair</a></li>
180 <li><a href="#h2-RETURN-VALUE">RETURN VALUE</a></li>
181 <li><a href="#h2-PORTABILITY">PORTABILITY</a></li>
182 <li><a href="#h2-SEE-ALSO">SEE ALSO</a></li>
183 <li><a href="#h2-AUTHOR">AUTHOR</a></li>