- Most of the window attribute routines are extensions of older routines
- which assume that color pairs are OR'd into the attribute parameter.
- These older routines use the same name, omitting an underscore (_).
+ The X/Open window attribute routines which set or get, turn on or off
+ are extensions of older routines which assume that color pairs are OR'd
+ into the attribute parameter. These newer routines use similar names,
+ because X/Open simply added an underscore (_) for the newer names.
+
+ The int datatype used in the legacy routines is treated as if it is the
+ same size as chtype (used by addch(3x)). It holds the common video at-
+ tributes (such as bold, reverse), as well as a few bits for color.
+ Those bits correspond to the A_COLOR symbol. The COLOR_PAIR macro pro-
+ vides a value which can be OR'd into the attribute parameter. For ex-
+ ample, as long as that value fits into the A_COLOR mask, then these
+ calls produce similar results:
+
+ attrset(A_BOLD | COLOR_PAIR(pair));
+ attr_set(A_BOLD, pair, NULL);
+
+ However, if the value does not fit, then the COLOR_PAIR macro uses only
+ the bits that fit. For example, because in ncurses A_COLOR has eight
+ (8) bits, then COLOR_PAIR(259) is 4 (i.e., 259 is 4 more than the limit
+ 255).
+
+ The PAIR_NUMBER macro extracts a pair number from an int (or chtype).
+ For example, the input and output values in these statements would be
+ the same:
+
+ int value = A_BOLD | COLOR_PAIR(input);
+ int output = PAIR_NUMBER(value);
The attrset routine is a legacy feature predating SVr4 curses but kept
in X/Open Curses for the same reason that SVr4 curses kept it: compati-
@@ -195,7 +228,7 @@
passed to addch (see curs_addch(3x)).
NameDescription
- -----------------------------------------------------------
+ -----------------------------------------------------------------
A_NORMAL Normal display (no highlight)
A_STANDOUT Best highlighting mode of the terminal.
A_UNDERLINE Underlining
@@ -208,6 +241,7 @@
A_ALTCHARSET Alternate character set
A_ITALIC Italics (non-X/Open extension)
A_CHARTEXT Bit-mask to extract a character
+ A_COLOR Bit-mask to extract a color (legacy routines)
These video attributes are supported by attr_on and related functions
(which also support the attributes recognized by attron, etc.):
@@ -240,6 +274,127 @@
support more than 256 color pairs.
+
+ X/Open Curses is largely based on SVr4 curses, adding support for
+ "wide-characters" (not specific to Unicode). Some of the X/Open dif-
+ ferences from SVr4 curses address the way video attributes can be ap-
+ plied to wide-characters. But aside from that, attrset and attr_set
+ are similar. SVr4 curses provided the basic features for manipulating
+ video attributes. However, earlier versions of curses provided a part
+ of these features.
+
+ As seen in 2.8BSD, curses assumed 7-bit characters, using the eighth
+ bit of a byte to represent the standout feature (often implemented as
+ bold and/or reverse video). The BSD curses library provided functions
+ standout and standend which were carried along into X/Open Curses due
+ to their pervasive use in legacy applications.
+
+ Some terminals in the 1980s could support a variety of video at-
+ tributes, although the BSD curses library could do nothing with those.
+ System V (1983) provided an improved curses library. It defined the A_
+ symbols for use by applications to manipulate the other attributes.
+ There are few useful references for the chronology.
+
+ Goodheart's book UNIXCursesExplained (1991) describes SVr3 (1987),
+ commenting on several functions:
+
+ o the attron, attroff, attrset functions (and most of the functions
+ found in SVr4 but not in BSD curses) were introduced by System V,
+
+ o the alternate character set feature with A_ALTCHARSET was added in
+ SVr2 and improved in SVr3 (by adding acs_map[]),
+
+ ostart_color and related color-functions were introduced by System
+ V.3.2,
+
+ o pads, soft-keys were added in SVr3, and
+
+ Goodheart did not mention the background character or the cchar_t type.
+ Those are respectively SVr4 and X/Open features. He did mention the A_
+ constants, but did not indicate their values. Those were not the same
+ in different systems, even for those marked as System V.
+
+ Different Unix systems used different sizes for the bit-fields in
+ chtype for characters and colors, and took into account the different
+ integer sizes (32-bit versus 64-bit).
+
+ This table showing the number of bits for A_COLOR and A_CHARTEXT was
+ gleaned from the curses header files for various operating systems and
+ architectures. The inferred architecture and notes reflect the format
+ and size of the defined constants as well as clues such as the alter-
+ nate character set implementation. A 32-bit library can be used on a
+ 64-bit system, but not necessarily the reverse.
+
+ YearSystemArchColorCharNotes
+ ----------------------------------------------------------------
+ 1992 Solaris 5.2 32 6 17 SVr4 curses
+ 1992 HPUX 9 32 no 8 SVr2 curses
+ 1992 AIX 3.2 32 no 23 SVr2 curses
+ 1994 OSF/1 r3 32 no 23 SVr2 curses
+ 1995 HP-UX 10.00 32 6 16 SVr3 "curses_colr"
+ 1995 HP-UX 10.00 32 6 8 SVr4, X/Open curses
+ 1995 Solaris 5.4 32/64 7 16 X/Open curses
+ 1996 AIX 4.2 32 7 16 X/Open curses
+ 1996 OSF/1 r4 32 6 16 X/Open curses
+
+ 1997 HP-UX 11.00 32 6 8 X/Open curses
+ 2000 U/Win 32/64 7/31 16 uses chtype
+
+ Notes:
+
+ Regarding HP-UX,
+
+ o HP-UX 10.20 (1996) added support for 64-bit PA-RISC processors
+ in 1996.
+
+ o HP-UX 10.30 (1997) marked "curses_colr" obsolete. That version
+ of curses was dropped with HP-UX 11.30 in 2006.
+
+ Regarding OSF/1 (and Tru64),
+
+ o These used 64-bit hardware. Like ncurses, the OSF/1 curses in-
+ terface is not customized for 32-bit and 64-bit versions.
+
+ o Unlike other systems which evolved from AT&T code, OSF/1 provid-
+ ed a new implementation for X/Open curses.
+
+ Regarding Solaris,
+
+ o The initial release of Solaris was in 1992.
+
+ o The xpg4 (X/Open) curses was developed by MKS from 1990 to 1995.
+ Sun's copyright began in 1996.
+
+ o Sun updated the X/Open curses interface after 64-bit support was
+ introduced in 1997, but did not modify the SVr4 curses inter-
+ face.
+
+ Regarding U/Win,
+
+ o Development of the curses library began in 1991, stopped in
+ 2000.
+
+ o Color support was added in 1998.
+
+ o The library uses only chtype (no cchar_t).
+
+ Once X/Open curses was adopted in the mid-1990s, the constraint of a
+ 32-bit interface with many colors and wide-characters for chtype became
+ a moot point. The cchar_t structure (whose size and members are not
+ specified in X/Open Curses) could be extended as needed.
+
+ Other interfaces are rarely used now:
+
+ o BSD curses was improved slightly in 1993/1994 using Keith Bostic's
+ modification to make the library 8-bit clean for nvi. He moved
+ standout attribute to a structure member.
+
+ The resulting 4.4BSD curses was replaced by ncurses over the next
+ ten years.
+
+ o U/Win is rarely used now.
+
+
This implementation provides the A_ITALIC attribute for terminals which
have the enter_italics_mode (sitm) and exit_italics_mode (ritm) capa-
@@ -305,9 +460,25 @@
WA_BOLD Extra bright or bold
WA_ALTCHARSET Alternate character set
- The XSI curses standard specifies that each pair of corresponding A_
- and WA_-using functions operates on the same current-highlight informa-
- tion.
+ XSI curses does not assign values to these symbols, nor does it state
+ whether or not they are related to the similarly-named A_NORMAL, etc.:
+
+ o The XSI curses standard specifies that each pair of corresponding
+ A_ and WA_-using functions operates on the same current-highlight
+ information.
+
+ o However, in some implementations, those symbols have unrelated val-
+ ues.
+
+ For example, the Solaris xpg4 (X/Open) curses declares attr_t to be
+ an unsigned short integer (16-bits), while chtype is a unsigned in-
+ teger (32-bits). The WA_ symbols in this case are different from
+ the A_ symbols because they are used for a smaller datatype which
+ does not represent A_CHARTEXT or A_COLOR.
+
+ In this implementation (as in many others), the values happen to be
+ the same because it simplifies copying information between chtype
+ and cchar_t variables.
The XSI standard extended conformance level adds new highlights A_HORI-ZONTAL, A_LEFT, A_LOW, A_RIGHT, A_TOP, A_VERTICAL (and corresponding
@@ -358,6 +529,7 @@