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+<!--
****************************************************************************
- * Copyright 2018-2019,2020 Thomas E. Dickey *
+ * Copyright 2018-2020,2021 Thomas E. Dickey *
* Copyright 1998-2016,2017 Free Software Foundation, Inc. *
* *
* Permission is hereby granted, free of charge, to any person obtaining a *
* sale, use or other dealings in this Software without prior written *
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- * @Id: curs_color.3x,v 1.63 2020/10/24 09:35:23 tom Exp @
+ * @Id: curs_color.3x,v 1.66 2021/09/04 19:42:20 tom Exp @
-->
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<STRONG>o</STRONG> Color RGB values are not settable.
+</PRE><H2><a name="h2-HISTORY">HISTORY</a></H2><PRE>
+ SVr3.2 introduced color support to curses in 1987.
+
+ SVr4 made internal changes, e.g., moving the storage for the color
+ state from <STRONG>SP</STRONG> (the <STRONG>SCREEN</STRONG> structure) to <STRONG>cur_term</STRONG> (the <STRONG>TERMINAL</STRONG> struc-
+ ture), but provided the same set of library functions.
+
+ SVr4 curses limits the number of color pairs to 64, reserving color
+ pair zero (0) as the terminal's initial uncolored state. This limit
+ arises because the color pair information is a bitfield in the <STRONG>chtype</STRONG>
+ data type (denoted by <STRONG>A_COLOR</STRONG>).
+
+ Other implementations of curses had different limits:
+
+ <STRONG>o</STRONG> PCCurses (1987-1990) provided for only eight (8) colors.
+
+ <STRONG>o</STRONG> PDCurses (1992-present) inherited the 8-color limitation from PC-
+ Curses, but changed this to 256 in version 2.5 (2001), along with
+ changing <STRONG>chtype</STRONG> from 16-bits to 32-bits.
+
+ <STRONG>o</STRONG> X/Open Curses (1992-present) added a new structure <STRONG>cchar_t</STRONG> to store
+ the character, attributes and color-pair values, allowing increased
+ range of color-pairs. Both color-pairs and color-values used a
+ signed <STRONG>short</STRONG>, limiting values to 15 bits.
+
+ <STRONG>o</STRONG> ncurses (1992-present) uses eight bits for <STRONG>A_COLOR</STRONG> in <STRONG>chtype</STRONG> val-
+ ues.
+
+ Version 5.3 provided a wide-character interface (2002), but left
+ color-pairs as part of the attributes-field.
+
+ Since version 6 (2015), ncurses uses a separate <STRONG>int</STRONG> for color-pairs
+ in the <STRONG>cchar_t</STRONG> values. When those color-pair values fit in 8 bits,
+ ncurses allows color-pairs to be manipulated via the functions us-
+ ing <STRONG>chtype</STRONG> values.
+
+ <STRONG>o</STRONG> NetBSD curses used 6 bits from 2000 (when colors were first sup-
+ ported) until 2004. At that point, NetBSD changed to use 10 bits.
+ As of 2021, that size is unchanged. Like ncurses before version 6,
+ the NetBSD color-pair information is stored in the attributes field
+ of <STRONG>cchar_t</STRONG>, limiting the number of color-pairs by the size of the
+ bitfield.
+
+
</PRE><H2><a name="h2-PORTABILITY">PORTABILITY</a></H2><PRE>
This implementation satisfies XSI Curses's minimum maximums for <STRONG>COLORS</STRONG>
and <STRONG>COLOR_PAIRS</STRONG>.
</li>
<li><a href="#h2-RETURN-VALUE">RETURN VALUE</a></li>
<li><a href="#h2-NOTES">NOTES</a></li>
+<li><a href="#h2-HISTORY">HISTORY</a></li>
<li><a href="#h2-PORTABILITY">PORTABILITY</a></li>
<li><a href="#h2-SEE-ALSO">SEE ALSO</a></li>
</ul>
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